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Advanced Synthesis of Materials for Intermediate-Temperature Solid Oxide Fuel Cells

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Advanced Synthesis of Materials for Intermediate-Temperature Solid Oxide Fuel Cells

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Solid-oxide fuel cells (SOFCs) technology has a substantial potential in the application of clean and efficient electric power generation. However, the widespread utilization of SOFCs has not been realized because the cost associated with cell fabrication, materials and maintenance is still too high. To increase its competitiveness, lowering the operation temperature to the intermediate range of around 500–800 °C is one of the main goals in current SOFCs research. A major challenge is the development of cell materials with acceptably low ohmic and polarization losses to maintain sufficiently high electrochemical activity at reduced temperatures. During the past few decades, tremendous progress has been made in the development of cell materials and stack design, which have been recently reviewed. SOFCs are fabricated from ceramic or cermet powders. The performances of SOFCs are also closely related to the ways in which the cell materials are processed. Therefore, the optimization of synthetic processes for such materials is of great importance. The conventional solid-phase reaction method of synthesizing SOFCs materials requires high calcination and sintering temperatures, which worsen their microstructure, consequently, their electrochemical properties. Various wet chemical routes have recently been developed to synthesize submicro- to nano-sized oxide powders. This paper provides a comprehensive review on the advanced synthesis of materials for intermediate-temperature SOFCs and their impact on fuel cell performance. Combustion, co-precipitation, hydrothermal, sol–gel and polymeric-complexing processes are thoroughly reviewed. In addition, the parameters relevant to each synthesis process are compared and discussed. The effect of different processes on the electrochemical performance of the materials is evaluated and optimization of the synthesis processes is discussed and some emerging synthetic techniques are also briefly presented.

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... The most common synthesis methods researched to optimize the conductivity and catalytic properties of LSCF powders are solidstate reaction and wet chemical synthesis methods. [9][10][11][12][13][14][15] The solidstate reaction method is attractive because of its low cost and simplicity; however, it requires high temperatures, often resulting in poor compositional homogeneity and low surface area. 9 Hence, researchers have favored preparing LSCF by the wet chemical synthesis methods, which include solution combustion, co-precipitation, sol-gel, and polymeric complexing. ...
... [9][10][11][12][13][14][15] The solidstate reaction method is attractive because of its low cost and simplicity; however, it requires high temperatures, often resulting in poor compositional homogeneity and low surface area. 9 Hence, researchers have favored preparing LSCF by the wet chemical synthesis methods, which include solution combustion, co-precipitation, sol-gel, and polymeric complexing. 9,[11][12][13][14][15] The use of solutions as starting materials ensures homogeneous mixing of precursors at the atomic level and lower calcination temperatures. ...
... 9 Hence, researchers have favored preparing LSCF by the wet chemical synthesis methods, which include solution combustion, co-precipitation, sol-gel, and polymeric complexing. 9,[11][12][13][14][15] The use of solutions as starting materials ensures homogeneous mixing of precursors at the atomic level and lower calcination temperatures. 9 As a result, many researchers have successfully prepared crystalline LSCF powders with fine and homogeneous particles using wet chemical synthesis methods. ...
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The thermochemical stability of lanthanum strontium cobalt ferrite (LSCF) processed between 1000 °C–1200 °C via the in situ carbon templating method was studied. This method generates high surface area ceramics at traditional solid oxide fuel cell (SOFC) sintering temperatures by generating a carbon template in situ and subsequently removing the template by oxidation at 700 °C. Argon processed samples produced an amorphous carbon template, whereas nitrogen tended to form graphitic carbon. Prior to the oxidation step, nitrogen samples comprised larger La 2 O 3 crystallites (22–40 nm) compared to argon (9–17 nm). Upon oxidation, argon samples resulted in a pure LSCF phase with surface areas in the 21–29 m ² ·g ⁻¹ range, whereas nitrogen samples contained significant impurities. This demonstrates that the size of La 2 O 3 crystallites formed during inert processing limited the ability to produce a pure LSCF phase. Symmetrical cells comprising nano-LSCF electrodes generated by the templating method were compared to cells sintered directly in air. Impedance results suggest that nano-LSCF cells and cells processed in air were dominated by interfacial charge transfer resistance and gas diffusion, respectively. The results map out conditions for preparing and integrating high surface area, nanostructured LSCF into SOFC electrodes at traditional sintering temperatures. Strategies for improving the interfacial resistance of nano-LSCF electrodes are discussed.
... Rare-earth (R) orthochromites, RCrO 3 , have been investigated in the past few decades due to their interesting physical properties and potential applications in many conventional devices such as catalytic converters [1], solid-oxide fuel cell [2], and gas sensors [3]. LaCrO 3 , the first member of this series of compounds, has been widely investigated in nanoand bulk crystalline forms because of its fascinating electrical and chemical properties [4][5][6]. ...
... This relaxation can be analyzed by the Arrhenius law, f max = f 0 exp(-E a /k B T ), where f 0 is the preexponential factor, E a is the activation energy, and k B is the Boltzmann constant. The E a values, determined from the Arrhenius fitting of ln( f ) vs 1000/T plots [ Fig. 4(c)], are 0.27 (1), 0.28 (1), 0.29 (1), 0.24 (2), and 0.28 (1) eV for x = 0, 0.25, 0.5, 0.75, and 1 compounds, respectively. These E a values are in good agreement with values reported for RCrO 3 compounds [25,40,41]. ...
... The derived values of E a from the above equation are ∼0.27 (1), 0.28 (1), 0.29 (1), 0.24 (2), and 0.27 eV (1), respectively, for x = 0, 0.25, 0.5, 0.75, and 1 compounds. These values of E a are close to the values obtained from the Arrhenius fitting of characteristic peak frequency ( f max ) [ Fig. 4(c)]. ...
... Copper doping lowers VTEC at y(Cu) = 0.1; however, further doping (y(Cu) = 0.2) slightly increases it. Overall, the VTEC value in the range (8-10) × 10 −6 K −1 are close to the TEC values of the commonly used electrolytes for the intermediate-temperature SOFCs [20][21][22]. The phase transition does not cause a significant volume jump, and an increase in VTEC is not as high as those registered in the dilatometric studies in [49]. ...
... eV. The presence of partial electronic conductivity in the proton-conducting electrolytes in humidified air [21,22] may facilitate the charge transport across the electrode/electrolyte interface, and this decreased both the polarization resistance and the activation energy of the polarization conductivity of the electrodes in contact with them. Additionally, chemical compatibility tests were performed, which demonstrated that there was no chemical interaction of the NCNCO02 electrode materials with all considered electrolytes up to 1100 • C, except for BCSCuO. ...
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In this study, Nd1.6Ca0.4Ni1−yCuyO4+δ-based electrode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) are investigated. Materials of the series (y = 0–0.4) are obtained by pyrolysis of glycerol-nitrate compositions. The study of crystal structure and high-temperature stability in air and under low oxygen partial pressure atmospheres are performed using high-resolution neutron and in situ X-ray powder diffraction. All the samples under the study assume a structure with Bmab sp.gr. below 350 °C and with I4/mmm sp.gr. above 500 °C. A transition in the volume thermal expansion coefficient values from 7.8–9.3 to 9.1–12.0 × 10−6, K−1 is observed at approximately 400 °C in air and 500 °C in helium.The oxygen self-diffusion coefficient values, obtained using isotope exchange, monotonically decrease with the Cu content increasing, while concentration dependence of the charge carriers goes through the maximum at x = 0.2. The Nd1.6Ca0.4Ni0.8Cu0.2O4+δ electrode materialdemonstrates chemical compatibility and superior electrochemical performance in the symmetrical cells with Ce0.8Sm0.2O1.9, BaCe0.8Sm0.2O3−δ, BaCe0.8Gd0.19Cu0.1O3−δ and BaCe0.5Zr0.3Y0.1Yb0.1O3−δ solid electrolytes, potentially for application in IT-SOFCs.
... The solid-state reaction method was initially adopted for the preparation of materials for these electrodes, due to the low cost of manufacture and simplicity, however, the high temperatures of calcination and sintering compromise their electrochemical properties. Aiming to overcome this problem, several routes the synthesis in solution have been developed, such as solution combustion synthesis (SCS), sol-gel, co-precipitation, methods with polymeric complexant, hydrothermal methods, spray pyrolysis, microwaves, among others [3,15,[82][83][84][85][105][106][107]. The main characteristic of these methods resides in obtaining a homogeneous mixture on an atomic scale of the components of the material, in order to guarantee a greater diffusion at a lower synthesis temperature. ...
... In this way, the method is able to control the size of the particles, their morphology, and specific surface area. The SCS method has been used in the preparation of materials for SOFC electrodes for more than twenty years [3,15,[82][83][84][85][102][103][104][105][106][107]. This technique allows the obtainment of materials with a good compositional homogeneity in a short time. ...
Article
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Currently, solution combustion synthesis (SCS) is considered a reproducible, flexible, and lowcost synthesis method for the preparation of nanomaterials. A new trend in the SCS method is the use of less polluting fuels, such as starch. The use of starch as fuel in SCS is very interesting for green chemistry, as it is renewable and has several advantages, including its abundance, low-cost, and non-toxicity. Objective This paper provides a comprehensive review of the SCS method using starch as fuel. The main advantages of using starch as fuel will be illustrated with a wide variety of examples, highlighting its impact on the preparation of nanomaterials for energy and environmental applications. Conclusion In a combustion reaction using starch as fuel, several positive effects are expected, such as non-violent propagation, combustion with the production of non-toxic gases (mainly CO2 and H2O), and development of pores during the release of gases. For example, several macroporous metal oxide foams were prepared using the SCS method, through an appropriate combination of urea and starch fuels. With this approach, it is possible to control the structure, lattice defects, crystallite size, specific surface area, porosity, and other characteristics of the synthetized nanomaterial. For example, by combining starch with other fuels, it is possible to control the concentration of lattice defects in metal oxides and modify the optical properties of these materials. These properties are of fundamental importance for the performance of these materials and their subsequent application in electrodes, electrocatalysts, and photocatalysts in the areas of energy and environment.
... Nowadays, yttria-stabilized zirconia (YSZ) is the most widely used ceramic electrolyte for SOFCs. However, the high operating temperature (over 1000°C) of this zirconia (ZrO 2 ) based electrolyte causes the search for new electrolytes [3,[4][5][6]. Because of this, ceria and bismuth oxide-based solid electrolytes are developed, which can operate at intermediate temperatures (600-1000°C). ...
... R. Kirkgeçit & H.Ö. Torun / Processing and Application of Ceramics 14[4] (2020) 314-320 ...
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In this study, pure CeO2 and Ce0.85La0.10M0.05O2 (M: Sm3+, Gd3+, Dy3+) solid electrolytes were synthesized using the sol-gel method and sintered at 1350?C for 12 h. X-ray diffraction (XRD) was used for crystal structure characterization of the ceramic solid electrolytes. After sintering, all prepared solid electrolytes were indexed to be cubic crystal lattices. The thermal properties of the prepared samples were investigated by thermogravimetric (TG) and differential thermal analysis (DTA) methods. The surface properties of the grain structure of the ceramic solid electrolytes were evaluated by scanning electron microscopy (FE-SEM) confirming the average grain size of about 1 ?m. The electrochemical impedance spectroscopy technique was used to investigate AC electrical properties of prepared solid electrolytes. The conductivity values at 750?C of the Ce0.85La0.10Sm0.05O2, Ce0.85La0.10Gd0.05O2 and Ce0.85La0.10Dy0.05O2 and pure CeO2 were found to be 1.10 ? 10?3 S/cm, 3.05 ? 10?4 S/cm, 8.85 ? 10?4 S/cm and 8.44 ? 10?10 S/cm, respectively. The characterization results showed that the La-Sm co-doped CeO2 sample can be used as a ceramic electrolyte in intermediate temperature solid oxide fuel cells (IT-SOFC).
... Microstructures produced by varying preparation procedures and calcination temperatures directly affect the specific surface area and ASR of LSCF cathodes with the same stoichiometry. The solid-state reaction was the first method utilized to generate ceramic powders due to its excellent selectivity, high yield, lack of solvents, and simplicity [65]. However, this process requires repeated cycles of milling, calcination at elevated temperatures (> 1000 °C), and grinding to produce powders with a high electrical conductivity. ...
Article
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Perovskite-structured La1-xSrxCo1-yFeyO3-δ (LSCF) is a promising mixed ionic/electronic-conducting material that exhibits excellent electro-catalytic activity toward oxygen reduction and oxygen evolution reactions. LSCF offers potential applications in many processes, such as electrodes for solid oxide fuel cells (SOFCs), oxygen sensors, and dense membrane for oxygen separation and thus have been studied extensively in various fields. However, its physical and electrochemical properties are substantially influenced by dopant concentration, dopant type and processing conditions (synthesis methods, composite cathode effect, fabrication conditions, and chromium poisoning). Understanding and correlating the effect of LSCF composition, its synthesis methods, fabrication conditions, and its parameters are essential to enhance the performance of LSCF cathode for high- to- intermediate temperature SOFC applications. This review emphasizes the importance of enhancing the performance of LSCF cathode by optimizing the influential factors to facilitate and expedite research and development efforts for SOFC commercialization in the near future. Various synthesis and fabrication methods used to prepare and fabricate LSCF and LSCF-based composite cathodes are discussed in detail. Moreover, their pros and cons in optimizing the microstructure of LSCF cathodes are highlighted. Finally, the strategies to improve the long-term microstructural stability and electrochemical performances of the LSCF cathode are discussed.
... (2) e intermediate compound formation [24,[26][27][28][29]: (3) Starting the LSCF formation, respectively [16,30,31]. ...
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The perovskite Lanthanum Strontium Cobalt Ferrite (LSCF) is investigated as the cathode material used in intermediate-temperature solid oxide fuel cells (IT-SOFCs). In the present study, La0.6−xDyxSr0.4Co0.2Fe0.8O3−δ (x = 0, 0.3, 0.6) was synthesized through the coprecipitation method. The obtained precipitate was calcined at 500, 700, 900, and 1000°С. Phase characterization of the synthesized LSCF and LDySCF powder before and after heat treatment at 700°С was carried out by X-ray diffraction (XRD) analysis. XRD patterns revealed that the perovskite phase was obtained at 700°С in all calcined samples. Chemical bond study to investigate the synthesis process was conducted using the Fourier transform infrared spectroscopy technique. Thermal analysis of DTA and TG has been utilized to investigate how the calcination temperature affects the perovskite phase formation. According to the STA results, the perovskite phase formation started at 551°С and completed at 700°С. The density values of synthesized powders were 6.10, 6.11, and 6.37 g·cm−3for the undoped and doped samples calcined at 700°С. Powder morphology was studied by field emission scanning electron microscopy (FE-SEM). The micrographs showed the spherical-shaped particles with the average particle size of 24–131 nm.
... Among the incorporated doped ceria, the La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.2Ce0.8O2-δ (LSCF-GDC) composite cathode is one of the most extensively studied candidates for IT-SOFCs applications [7,[13][14][15][16][17]. However, the surface oxygen exchange kinetics are still slow at reduced temperatures. ...
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The effects of the electrochemical oxygen reduction reaction (ORR) on the surface of single-phase perovskite cathodes are well understood, but its potential for use in a complex system consisting of different material types is unexplored. Herein, we report how BaCO3 nanoparticles-modified La0.6Sr0.4Co0.2Fe0.8O3-δ-Gd0.2Ce0.8O2-δ (LSCF–GDC)-composite cathodes improved the electrochemical oxygen reduction kinetics for high-performing ceramic fuel cells. Both X-ray diffraction (XRD) and thermogravimetric analysis (TGA) studies reveal that BaCO3 is stable, and that it does not show any solid-state reaction with LSCF–GDC at SOFCs’ required operating temperature. The electrochemical conductivity relaxation (ECR) study reveals that during the infiltration of BaCO3 nanoparticles into LSCF–GDC, the surface exchange kinetics (Kchem) are enhanced up to a factor of 26.73. The maximum power density of the NiO-YSZ anode-support cell is increased from 1.08 to 1.48 W/cm2 via surface modification at 750 °C. The modified cathode also shows an ultralow polarization resistance (Rp) of 0.027 Ω.cm2, which is ~4.4 times lower than that of the bare cathode (~0.12 Ω.cm2) at 750 °C. Such enhancement can be attributed to the accelerated oxygen surface exchange process, possibly through promoting the dissociation of oxygen molecules via the infiltration of BaCO3 nanoparticles. The density functional theory (DFT) illustrates the interaction mechanism between oxygen molecules and the BaCO3 surface.
... So SOFCs can only operate at high temperatures. Such conditions are inevitably associated with many drawbacks limiting SOFCs commercialization, such as restriction of the compatible cell materials, unacceptable performance and electrode degradation rates, requirement of large input energy to heat the cell stacks, long start-up and shut-down cycles and so on [7][8] [9] [10] . In order to increase SOFCs competitiveness, it is necessary to lower the operating temperature down to the intermediate temperature (IT) range (600°C-800°C) or even to the low temperature (LT) range (400°C-600°C). ...
Article
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A new cation-deficient Ca-doping lanthanum tungstate compound with the exact formula Ca2.06La2.61□0.33W2O12 (□ indicating a vacancy) is presented in this work. It crystallizes in the space group R 3¯ C (No.167), Z = 18 with the hexagonal parameters a = 9.7747(1) Å and c = 55.7833(4) Å, similar to Ca5Re2O12. This compound belongs to a rare small crystallographic family A5B2X12 having large cells. The thermodynamic and kinetic processes of synthesizing this white powder compound are very slow. Its structure is analyzed by X-ray, neutron powder and electron diffraction. The conduction properties are investigated with complex impedance spectroscopy.
... Detailed discussion into how these synthetic processes work and how they can be tailored can be found in several more relevant and informative reviews published elsewhere. 14,39 It is noted that the synthetic method should be elaborately selected and modified based on the target application of BSCF. 6 In the early stages of SOFC development, a typical configuration of SOFC is La 0.8 Sr 0.2 MnO 3 (LSM) cathode | yttria-stabilized zirconia (YSZ) electrolyte | Ni + YSZ anode. ...
... Gadolinium-doped ceria (Gd 0.2 Ce 0.8 O 2-δ , GDC) pow-ders were prepared by a sol-gel method as described elsewhere [13]. The powders were pressed under 150 MPa into discs with diameter of 11 mm and thickness of 0.5 mm and finally sintered at 1250°C for 2 h to obtain a dense electrolyte. ...
Article
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Novel cathode materials for solid oxide fuel cells based on Ba-doped Sr2Fe1.5Mo0.5O6 (Sr2-xBaxFe1.5Mo0.5O6-? where x = 0.3, 0.5, 0.7 and 0.9) were synthesized by solution combustion method and sintered at 1200?C. Their phase composition, microstructure and electrical conductivity were studied. It was shown that the maximal electrical conductivity of 18.5 S/cm at 450?C was measured for the Sr1.3Ba0.7Fe1.5Mo0.5O6-? ceramics. The superior chemical compatibility between the Sr2-xBaxFe1.5Mo0.5O6-? cathode and Gd0.2Ce0.8O1.9 electrolyte was confirmed, as well as good matching between thermal expansion coefficients of the cathode and electrolyte materials.
... Among them, high temperature solid oxide fuel cells (SOFCs) are the cleanest, most efficient and versatile electrochemical energy conversion systems [1]. Due to the employment of all solid-state, oxide-based components and high operation temperatures (500-1000 o C), SOFCs show many superiorities over the conventional energy conversion technologies with very high efficiency without Carnot limitation (70%-80%), sustainability (substantial reduction in CO 2 emission and very low levels of NO x and SO x emissions), low materials cost, modularity and fuel flexibility [2][3][4][5][6]. In addition to hydrogen, various fuels such as hydrocarbon, hydrocarbon-derived fuels, solid carbon and ammonia can be used for SOFCs system [7][8][9][10][11][12][13]. ...
Article
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High temperature solid oxide fuel cell (SOFC) is the most efficient and clean energy conversion technology to electrochemically convert the chemical energy of fuels such as hydrogen, natural gas and hydrocarbons to electricity, and also the most viable alternative to the traditional thermal power plants. However, the power output of a SOFC critically depends on the characteristics and performance of its key components: anode, electrolyte and cathode. Due to the highly reducing environment and strict requirements in electrical conductivity and catalytic activity, there are limited choices in the anode materials of SOFCs, particularly for operation in the intermediate temperature range of 500-800 o C. Among them, Ni-based cermets are the most common and popular anode materials of SOFCs. The objective of this paper is to review the development of Ni-based anode materials in SOFC from the viewpoints of materials microstructure, performance and industrial scalability associated with the fabrication and optimization processes. The latest advancement in nano-structure architecture, contaminant tolerance and interface optimization of Ni-based cermet anodes is presented. And at the end of this paper, we propose and appeal for the collaborative work of scientists from different disciplines that enable the inter-fusion research of fabrication, microanalysis and modelling, aiming at the challenges in the development of Ni-based cermet anodes for commercially viable intermediate temperature SOFC or IT-SOFC technologies. Keywords: Ni-based cermet anode, intermediate temperature solid oxide fuel cell, activity, interface optimization, carbon deposition, sulfur poisoning, multidisciplinary collaborative work. J o u r n a l P r e-p r o o f 2
... Fast ionic transport is highly desired by solid oxide fuel cells (SOFCs), as high ionic conduction of electrolytes and electrodes is directly linked to superb power outputs, robust durability, and the rapid start-up of fuel cells [1,2]. However, the electrolyte always requires ionic conductivity as high as 0.1 S cm −1 to achieve favorable performance. ...
Article
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Since colossal ionic conductivity was detected in the planar heterostructures consisting of fluorite and perovskite, heterostructures have drawn great research interest as potential electrolytes for solid oxide fuel cells (SOFCs). However, so far, the practical uses of such promising material have failed to materialize in SOFCs due to the short circuit risk caused by SrTiO 3 . In this study, a series of fluorite/perovskite heterostructures made of Sm-doped CeO 2 and SrTiO 3 (SDC–STO) are developed in a new bulk-heterostructure form and evaluated as electrolytes. The prepared cells exhibit a peak power density of 892 mW cm ⁻² along with open circuit voltage of 1.1 V at 550 °C for the optimal composition of 4SDC–6STO. Further electrical studies reveal a high ionic conductivity of 0.05–0.14 S cm ⁻¹ at 450–550 °C, which shows remarkable enhancement compared to that of simplex SDC. Via AC impedance analysis, it has been shown that the small grain-boundary and electrode polarization resistances play the major roles in resulting in the superior performance. Furthermore, a Schottky junction effect is proposed by considering the work functions and electronic affinities to interpret the avoidance of short circuit in the SDC–STO cell. Our findings thus indicate a new insight to design electrolytes for low-temperature SOFCs.
... High operating temperature~1000°C narrows down the spectrum of materials that can be used as interconnect and sealants, and it limits the field of application of SOFCs. Besides, the time length required to heat up the system to this high operating temperature is rather long (Kharton et al., 2004;Shao et al., 2012). Further, mismatching of thermal expansion coefficient of various components of SOFC leads to cracking and spallation, which results in degradation of cell performance. ...
... Namun begitu, suhu kalsin (T c ) yang tinggi yang lazimnya melebihi 1000 °C dan proses pengisaran yang berulang-ulang dalam tempoh yang lama untuk menghasilkan serbuk berfasa tunggal perovskit oksida adalah kelemahan utama kaedah SSR ini. Serbuk yang terhasil pula mempunyai ketulenan yang rendah dan sifat mikrostruktur yang tidak homogen (Shao et al. 2012;Vahid Mohammadi & Cheng 2015). Disebabkan oleh kelemahan-kelemahan tersebut, WCM seperti kaedah sol-gel seringkali mendapat perhatian untuk digunakan dalam penghasilan serbuk perovskit oksida kerana kemampuan kaedah ini untuk menghasilkan serbuk dengan ketulenan dan kehomogenan mikrostruktur yang lebih tinggi pada T c yang jauh lebih rendah berbanding kaedah SSR (Ismail et al. 2020;Wang et al. 2015;Zeng & Huang 2017). ...
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Sifat penguraian terma dan pembentukan fasa bahan lantanum strontium kobalt oksida, La0.6Sr0.4CoO3-δ (LSC) yang disediakan melalui kaedah sol-gel berbantu agen kimia berbeza, iaitu agen serakan, agen pempolimeran dan agen permukaan aktif atau surfaktan telah dicirikan secara sistematik masing-masing melalui analisis termogravimetrik (TG) dan pembelauan sinar-X (XRD). Penguraian terma bahan organik dan bahan bukan organik yang tidak diperlukan dalam serbuk pelopor bahan LSC telah lengkap pada suhu kurang daripada 1000 °C bagi serbuk pelopor yang disediakan dengan menggunakan agen serakan dan agen pempolimeran, dan suhu melebihi 1000 °C bagi serbuk pelopor yang disediakan dengan menggunakan surfaktan. Sifat penguraian terma ini dipengaruhi oleh suhu pengeringan serbuk pelopor tersebut dan berat molekul agen kimia. Pembentukan fasa tunggal perovskit LSC telah disahkan dalam serbuk pelopor yang disediakan dengan menggunakan agen serakan, iaitu karbon teraktif dan agen pempolimeran, iaitu etilena glikol selepas serbuk pelopor tersebut dikalsin pada suhu 900 °C. Sebaliknya, fasa tunggal perovskit LSC tidak terbentuk secara lengkap dalam serbuk pelopor yang disediakan dengan menggunakan surfaktan (polietilena glikol, Triton-X-100, Brij-97 dan Tween-80) walaupun selepas serbuk pelopor tersebut telah dikalsin pada suhu yang lebih tinggi iaitu 1100 °C. Kepekatan surfaktan, nisbah molar surfaktan kepada logam kation dan nilai pH larutan bahan pelopor yang tidak sesuai telah menyumbang kepada keputusan tersebut.
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Intermediate temperature solid oxide fuel cells oxygen electrodes are modified by active interfacial layers. Spray pyrolysis is used to produce thin (≈500 nm) layers of mixed ionic and electronic conductors: Sm0.5Sr0.5CoO3−δ (SSC), La0.6Sr0.4CoO3−δ (LSC), La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF), and Pr6O11 (PrOx) on the electrode–electrolyte interface. The influence of the annealing temperature on the electrode polarization (area specific resistance—ASRpol) is investigated by impedance spectroscopy of symmetrical electrodes in the temperature range of 400–700 °C. The results show that the introduction of nanocrystalline interlayers promotes an oxygen reduction reaction by extending the active surface area and improved contact between the electrode and the electrolyte. Introducing LSCF, LSC, or SSC interlayer reduces ASRpol by a factor of 4 and PrOx by a factor of 2 against the reference, powder processed LSCF electrode. At 600 °C, the obtained ASRpol values for PrOx, LSCF, LSC, and SSC interlayer are 245, 137, 119, and 107 mΩ cm2, which can be considered very low in comparison to standard powder processed oxygen electrodes. Anode supported single cell with developed LSC/LSCF electrode reveals ≈1.2 W cm−2 power output at 600 °C and maintains stable cell voltage of 0.75 V under 1 A cm−2 during 60 h of the test. Solid oxide fuel cell oxygen electrode is improved by introducing a nanocrystalline interlayer of electrochemically active oxide between the electrolyte and oxygen electrode. Active interfacial layers are fabricated by spray pyrolysis technique. The microstructure and crystallization of the active interfacial layer are investigated. The symmetrical cells and solid oxide cells with active interfacial layer show an improved electrochemical performance.
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Electron, proton and oxygen-triple-conducting materials are becoming the dominant steam electrode candidate to break the rate limit on the water-splitting reaction that throttles the performance of protonic ceramic electrolysis cells (PCECs). In this study, based on Pr2NiO4+δ Ruddlesden-Popper phase, we manipulate these conductivities by Pr-site Ba substitution to probe the correlation of each conductivity with the kinetics of the elementary reaction steps. It is found that the proton conductivity is vital to sustain an extended active surface area for faster adsorption of reactants and desorption of products. The effect of oxygen conductivity is surprisingly found insignificant in the water-splitting reaction. On the contrary, surface oxygen removal is discovered as the most rate-limiting process. The electronic conductivity is not a direct limiting factor. However, an electron transfer process between the current collector and the electrode junction could introduce extra resistance that is perceptible at a high operating temperature range. The best water-splitting activity is obtained on a proton conductivity/oxygen surface desorption capability well-balanced sample after Ba substitution. As a result, a water-splitting reaction resistance of 0.022 Ωcm², a current density of 1.96 A/cm² at 700 °C is achieved on Pr1.7Ba0.3NiO4+δ, one of the best performances for PCECs.
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First-principles calculations were conducted, which proposed that members of the RE3GaO6 (RE = rare earth) system were oxide ion conductors. This study experimentally verified oxide ion conduction in Dy3GaO6, Er3GaO6, and Nd3GaO6. The sintered bodies were synthesized by a solid-state reaction method, and their properties were characterized. The samples with dopants were observed to be mixed electron and oxide ion conductors. Dy2.85Ca0.15GaO6-δ exhibited oxide ion conductivities of 2.1 × 10⁻⁴ S/cm at 973 K, with an oxide ion transport number of 21 % under O2 gas flow. Additionally, the Rietveld refinement suggested that oxide ion migration might occur via the oxide ion vacancy between the O2 sites. Overall, the oxide ion conductivities of RE3GaO6 increased in the following order: Nd > Dy > Er, which was in good agreement with that predicted by using the first-principles calculations. The discrepancy between the experimentally measured and predicted conductivities was caused by the solid-solution limit at the RE site for the dopants.
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Symmetrical solid oxide fuel cells (SSOFCs) could be alternative energy conversion devices due to their simple fabrication process and low-cost. Herein, perovskite La0.6Ce0.1Sr0.3Fe0.95Ru0.05O3–δ (LCSFR) was synthesized and evaluated as a high-performance electrode for SSOFCs based on the electrolyte of La0.9Sr0.1Ga0.8Mg0.2O3–δ (LSGM). LCSFR retains their stable perovskite crystal structure in both reducing and oxidizing atmospheres, though a minor amount of LaSrFeO4 phase is present under reducing conditions. Morphology investigation shows that homogeneously dispersed Ru metallic nanoparticles were exsolved on the surface of LCSFR after being reduced. The polarization resistance (Rp) of the LCSFR-CGO (Ce0.9Gd0.1O2–δ) is about 0.11 Ω∙cm² at 800 °C in air, while the value of Rp for LCSFR-CGO in wet H2 (3% H2O) increases up to 0.32 Ω∙cm². The symmetrical LCSFR-CGO|LSGM|LCSFR-CGO cell demonstrates a performance with an open circuit potential (OCV) of 1.07 V and a maximum peak power density of 904 mW/cm² at 800 °C using wet H2 (3% H2O) as the fuel. This high performance indicates that LCSFR is a candidate electrode for SSOFCs.
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Solid oxide fuel cells (SOFCs) and electrolysis cells (SOECs) are promising energy conversion devices, on whose basis green hydrogen energy technologies can be developed to support the transition to a carbon-free future. As compared with oxygen-conducting cells, the operational temperatures of protonic ceramic fuel cells (PCFCs) and electrolysis cells (PCECs) can be reduced by several hundreds of degrees (down to low-and intermediate-temperature ranges of 400-700 C) while maintaining high performance and efficiency. This is due to the distinctive characteristics of charge carriers for proton-conducting electrolytes. However, despite achieving outstanding lab-scale performance, the prospects for industrial scaling of PCFCs and PCECs remain hazy, at least in the near future, in contrast to commercially available SOFCs and SOECs. In this review, we reveal the reasons for the delayed technological development, which need to be addressed in order to transfer fundamental findings into industrial processes. Possible solutions to the identified problems are also highlighted.
Article
In this study, we report a high performance and redox-stable symmetrical solid oxide fuel cell (SOFC) based on (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ (BSMF) electrode and La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) electrolyte. BSMF is able to operate both as anode and cathode. Excellent electrocatalytic activity has been achieved on BSMF towards hydrogen oxidation and oxygen reduction. Due to its closely matched lattice parameter to LSGM electrolyte, a unique diffuse interface is formed between BSMF and LSGM. Compared to a clean interface, e.g. BSMF/gadolinium doped ceria interface, this diffuse interface promotes the performance of BSMF electrode 1–1.8 times in 600–800 °C. Polarization resistance of the BSMF/LSGM specimen is as low as 0.047 and 0.007 Ωcm² in humidified H2 and in air at 800 °C, respectively. On the BSMF/LSGM/BSMF symmetrical cell, a maximum power density of 2.28 W/cm² is achieved at 800 °C, the highest among with redox-stable ceramic electrodes to the best of our knowledge. Redox stability of this cell is confirmed. The role of anode and cathode is reversed back and forth in different operation modes. No apparent degradation is observed through 4 cycles within a 110 h operation period. These findings demonstrate that (Ba0.5Sr0.5) (Mo0.1Fe0.9)O3-δ coupled with LSGM electrolyte is an excellent choice to build a high performance, redox-stable SOFC.
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In this work, a highly active cathode with perovskite structure for solid oxide fuel cell (SOFC) is designed. The structural, chemical compatibility, and electrochemical properties of Sr2Fe1.5Mo0.5O6 partially doped with Cu (Sr2Fe1.5−xCuxMo0.5O6−δ, SFCxM) are investigated. The results show that SFCxM retains the perovskite structure when Fe element in Sr2Fe1.5Mo0.5O6 is partially replaced by Cu, but its unit cell expands as the doping amount of Cu increasing. The thermal expansion coefficient of Sr2Fe1.5Mo0.5O6 increases with Cu doping remarkably, so doping with excessive Cu is not conducive to the chemical compatibility between SFCxM cathode and samarium-doped ceria (SDC) electrolyte. Analysis of SFCxM cathode impedance data indicates that the properties of Sr2Fe1.5−xCuxMo0.5O6−δ cathode can be improved by Cu substitution. The conductivity of Sr2Fe1.5Mo0.5O6 (SFM) is improved by doping with appropriate content of Cu, while the interface impedance of the SFCxM cathode decreases with Cu doping and reaches the smallest value of 0.26 Ω cm² at the dopant content of x = 0.1. Furthermore, the interface impedance of the composite cathode consists of appropriate mass ratio of SFC0.1M, and SDC is lower than that of SFC0.1M. As a result, the composite cathode consists of appropriate mass ratio of SFC0.1M, and SDC is a potential cathode material for solid oxide fuel cell.
Article
Intermediate temperature solid oxide fuel cells (IT-SOFCs) have been extensively studied due to high efficiency, cleanliness, and fuel flexibility. To develop highly active and stable IT-SOFCs for the practical application, preparing an efficient cathode is necessary to address the challenges such as poor catalytic activity and CO2 poisoning. Herein, an efficient optimized strategy for designing a high-performance cathode is demonstrated. By motivating the phase transformation of BaFeO3-δ perovskites, achieved by doping Pr at the B site, remarkably enhanced electrochemical activity and CO2 resistance are thus achieved. The appropriate content of Pr substitution at Fe sites increases the oxygen vacancy concentration of the material, promotes the reaction on the oxygen electrode, and shows excellent electrochemical performance and efficient catalytic activity. The improved reaction kinetics of the BaFe0.95Pr0.05O3-δ (BFP05) cathode is also reflected by a lower electrochemical impedance value (0.061 Ω·cm2 at 750 °C) and activation energy, which is attributed to high surface oxygen exchange and chemical bulk diffusion. The single cells with the BFP05 cathode achieve a peak power density of 798.7 mW·cm-2 at 750 °C and a stability over 50 h with no observed performance degradation in CO2-containing gas. In conclusion, these results represent a promising optimized strategy in developing electrode materials of IT-SOFCs.
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To commercialize solid oxide fuel cells, many methods for reducing the production time of manufacturing a fuel cell membrane-electrode-assembly (MEA) using a non-vacuum process have been studied and still the post-heat treatment process is an issue. This paper discusses an alternative sintering method to replace the conventional thermal sintering step for ceramic thin film fabrication, which is time consuming and costly. We fabricated samarium-doped ceria (SDC) thin films, which has high ionic conductivity and high surface exchange coefficient for oxygen reactions at the cathode side. The films were deposited by chemical solution deposition (CSD) method utilizing electrostatic spray deposition (ESD) technique. Thermal decomposition and crystallization steps are required as a post-heat treatment process to obtain desired material properties. For this purpose, the flash light sintering method is adopted and compared with the conventional thermal sintering process using halogen furnace. With this flash light sintering method, the conventional post-heat treatment process time can be significantly reduced from tens of hours to a few seconds. Scanning electron microscopy, X-ray diffraction, and transmission electron microscopy analyses were carried out for material characterizations. Additionally, electrochemical impedance analysis and current-voltage behavior measurements were conducted. By successful fabrication of SDC cathodic functional layer utilizing flash light irradiation process, the 2-folds of fuel cell performance enhancement was obtained in terms of the peak power density at the measurement temperature of 450 oC.
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A composite material of La 0.6 Sr 0.4 CoO 3-δ- BaCe 0.54 Zr 0.36 Y 0.1 O 2.95 (LSC-BCZY) was prepared by mixing sol-gel derived LSC and BCZY powders in different weight percentage (wt%) ratio of LSC to BCZY (LSC:BCZY). The prepared composite powders were denoted as S1 (30:70), S2 (50:50) and S3 (70:30). The powders were characterized by an X-ray diffractometer (XRD), a Brunauer-Emmett-Teller (BET) surface area and porosity analyzer and a scanning electron microscope (SEM) equipped with an energy dispersive X-ray (EDX) spectrometer. XRD analysis confirmed that all of the powders were not pure enough due to the presence of impurity phases such as barium carbonate (BaCO 3 ) and strontium carbonate (SrCO 3 ) and unknown phases. S1 powder has the highest amount of impurity phases (81.19 %) and the largest BET surface area (4.82 m ² g ⁻¹ ). All of the powders formed typical clump-like network structure as proven by SEM analysis. EDX analysis revealed that the elemental compositions of La, Sr and Zr were deviated from their nominal mole fractions in all powders due to the Zr-rich clusters formation. The results indicate that the formation of pure and homogenous LSC-BCZY composite powder prepared by solid state mixing method requires further modification and improvement of the preparation method.
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FeTiO2 thin films are prepared by sol–gel dip coating technique at room temperature. The X-ray Diffraction (XRD) analysis confirms the good crystalline nature of the prepared thin films and the UV–Vis Spectroscopic results revealed an optical band gap value around 3.11 eV. The electrical property from I-V represented an increase in electric field with corresponding increase in current density. The prepared thin films are used in the construction of P-N junction diode. The design and construction of the P-N junction diode has been elaborated here. The diode performance has been studied through the voltage Vs current characteristic graphs. The diode parameters of ideality factor (n) and barrier height (Φb) of n-FeTiO2/p-Si is calculated from the I-V measurements in darkness and under the illumination using J-V method. The value of ideality factor n for n-FeTiO2/p-Si diode is 6.88 in dark but under light, it increases to 7.51.
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The current work principally treats the significant aspects of solid electrolytes based on cerium oxide in the absence and presence of potassium bicarbonate. The classic oxide electrolyte (LCDC) and the bicarbonate nanocomposite electrolyte @KHC (LCDC@KHC) are synthesized separately via self‐combustion and co‐precipitation techniques. Structural, thermal, electro‐morphological and electrochemical properties of pure LCDC and nanocomposite material LCDC@KHC are carefully examined. In particular, the influence of the heavily coupling amongst LCDC oxide and KHCO3 bicarbonate on the microstructures and ionic conductivities of KHCO3‐coated nanocrystalline LCDC is studied by TG/DTA, Raman, FEGSEM and AC impedance spectroscopy. Thermal analyses show that the LCDC@KHC nacomposite is stable at a temperature below 122 °C. Beyond this temperature, the LCDC@KHC nanocomposite is transformed into a LCDC@ nanocomposite. XRD data confirms that the LCDC phase and the various nanocomposite materials LCDC@KHC, sintering at different temperatures, adopt the fluorite structure. Lattice parameters and bond lengths are determined by Rietveld refinement. The ionic conductivity of bicarbonate nanocomposite electrolyte LCDC@KHC is 100 to 1000 times higher than that of the novel classic electrolyte LCDC. The remarkable enhancement of conductivity as a function of temperature rise is correlated to the presence of potassium in two forms: bicarbonate and carbonate in the LCDC@ nanocomposite electrolyte. Herein, we report the synthesis of Ce0.7La0.15Ca0.15O2‐d and Ce0.7La0.15Ca0.15O2‐d@KHCO3 electrolytes through self‐combustion and co‐precipitation techniques. TG/DTA, XRD, Raman, FEGSEM and AC impedance spectroscopy are used to study the thermal, structural, electro‐morphological and electrochemical properties. The present studies offer an inexpensive method to develop a new category of composite solid electrolytes (CSE), in particular ceria‐carbonate (3 C) composites, and will help us in future studies to investigate their new applications as promising electrolyte compounds for low temperature fuel cell technology.
Article
A novel strategy was proposed to enhance the sinterability and electrical properties of BaZr0.1Ce0.7Y0.2O3‐δ (BZCY) proton‐conducting electrolyte by adding 10 wt.% La0.9Sr0.1Ga0.8Mg0.2O3‐δ (LSGM) to form a 90 wt.% BZCY–10 wt.% LSGM (BL91) composite electrolyte. XRD patterns showed that no reaction occurred between the BZCY and LSGM electrolytes after sintering at 1400°C, 1450°C, 1500°C, and 1550°C for 10 h. The BL91 composite electrolyte exhibited higher relative densities and Vickers hardness and excellent electrical properties compared with those of the BZCY electrolyte. A combined approach of equivalent circuit model and distribution of relaxation time analysis was used to distinguish the bulk and grain‐boundary contributions to the total conductivity and electrode processes. The introduction of 10 wt.% LSGM serves as a grain‐boundary pinning phase, which can reduce the mobility of grain boundaries, thereby increasing sintered density and enhancing conductivity in BL91. A solid oxide fuel cell with proton‐conducting BL91 and BZCY membranes was tested, in which the former displayed higher power outputs than the latter. Ohmic and interfacial polarization resistances decreased by approximately 20%, thereby revealing the remarkable electrical properties of the BL91 electrolyte. Results demonstrated that BL91 composite is a development prospect proton‐conducting electrolyte.
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Regardless of the manufacturing process such as solid-state reaction, sol-gel, etc., applied in obtaining anodes in solid oxide fuel cells (SOFCs), Sr2MgMoO6-δ (SMMO) double perovskites are recognized worldwide and widely used as anodic material with potential application in SOFC. This is due to several factors such as high electronic conductivity, high electrocatalytic activity, structural stability under reducing atmosphere, high transition temperature, giant magnetoresistance, reasonable tolerance to carbon formation, and its desired ability to reduce sulfur poisoning. In this review article, the advances of the SMMO double perovskite are analyzed.
Article
Nickel ferrite (NiFe2O4) nanoparticles were synthesized through the sol-gel auto-combustion method using urea and glycine as mixed fuel. The prepared nanoparticles were investigated for their structural, optical, and magnetic characterizations. Rietveld refined X-ray diffraction (XRD) patterns revealed the development of single-phase cubic spinel. The crystallite size was calculated by using Modified Scherrer's method and the W-H plot was found in the order of 26.6 nm and 25.4 respectively which are nearly the same. The infrared spectrum showed the typical characteristic absorption bands in the range of 400 cm⁻¹ to 600 cm⁻¹ belonging to cubic spinel structure. Scanning electron microscopy images showed the spherical nature of the nanoparticles along with agglomeration to some extent. As per the optical study, the prepared nanoparticles have an optical bandgap of 2.59 eV. The magnetic properties were studied through the M − H hysteresis curve showing superparamagnetic nature, the value of saturation magnetization (Ms), coercivity (Hc) was observed 46.20 emu/gm, and 383.2 Oe respectively. The photocatalytic activity of nickel ferrite was studied based on the degradation of methylene blue (MB) dye as a model compound, where the result showed that prepared nanoparticles possessed a good photocatalytic activity against dye degradation. Up to four times catalyst exhibits nearly the same reutilization.
Article
The adaption of the sol-gel autocombustion method to the Cu/ZrO2 system opens new pathways for the specific optimisation of the activity, long-term stability and CO2 selectivity of methanol steam reforming (MSR) catalysts. Calcination of the same post-combustion precursor at 400 °C, 600 °C or 800 °C allows accessing Cu/ZrO2 interfaces of metallic Cu with either amorphous, tetragonal or monoclinic ZrO2, influencing the CO2 selectivity and the MSR activity distinctly different. While the CO2 selectivity is less affected, the impact of the post-combustion calcination temperature on the Cu and ZrO2 catalyst morphology is more pronounced. A porous and largely amorphous ZrO2 structure in the sample, characteristic for sol-gel autocombustion processes, is obtained at 400 °C. This directly translates into superior activity and long-term stability in MSR compared to Cu/tetragonal ZrO2 and Cu/monoclinic ZrO2 obtained by calcination at 600 °C and 800 °C. The morphology of the latter Cu/ZrO2 catalysts consists of much larger, agglomerated and non-porous crystalline particles. Based on aberration-corrected electron microscopy, we attribute the beneficial catalytic properties of the Cu/amorphous ZrO2 material partially to the enhanced sintering resistance of copper particles provided by the porous support morphology.
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Symmetrical solid oxide cells (SSOCs) with identical air and fuel electrodes have gained significant scientific interest in the last decade because they offer several advantages over conventional cell configurations. Among other features, simpler fabrication, better chemical and thermo-mechanical compatibility between cell layers, and electrode reversibility, make them attractive for electricity generation, H2 production and CO2 electroreduction. This review offers an overview of the most recent advances in the field of SSOCs, paying special attention to the relationship between electrode composition, crystal structure and properties. With that aim, symmetrical electrodes are classified in four groups according to their redox stability, i.e. single phases, composites, electrodes with exsolved metal particles and those that suffer a drastic phase transformation under reducing conditions, known in the literature as quasi-symmetrical electrodes. Furthermore, an outlook of other cell configurations with increased scientific interest are also discussed, i.e. symmetrical protonic fuel cells (H–SSOCs) and solid oxide electrolyzers for CO2 electroreduction. With this overview in mind, the authors would like to highlight the challenge ahead of finding electrode materials that optimally work under both oxidizing and reducing conditions in terms of redox stability and electrochemical properties, and further conclude on the future development of SSOCs.
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Recently, a novel composite solid oxide fuel cell electrode fabrication method based on ethylene glycol (EG)-based polymeric precursors, which yielded long triple phase boundaries and thus, high performance, was developed. However, some of these coatings were reported to contain randomly formed, large pores. Since porosity observed in the microstructure may impact the electrochemical performance directly, the origin of its formation and ways to eliminate it were investigated in the present study. We hypothesized that the large pores detected in microstructure were related to incomplete polymerization which resulted in instant discharge of carbonaceous gases and that promoting further polymerization by adding extra nitric acid would eliminate these pores. Thermal analyses revealed that when liquid La0.8Sr0.2FeO3–Ce0.8Sm0.2O2 (LSF-SDC) precursors without additional nitric acid were heated, an abrupt weight loss took place at 200 °C in the case of polymeric solutions. Addition of nitric acid resulted in a weight loss that took place over a temperature range of 200–400 °C. Microstructural analyses showed large pores in LSF-SDC films, especially in the case of thick (ca. 4–4.5 μm) samples. These large pores were mostly eliminated upon nitric acid addition. Electrochemical impedance spectroscopy measurements revealed ca. 60% reduction in the polarization resistance of the thick electrodes upon nitric acid addition, due to the elimination of large pores and thus enhancement of the triple phase boundary length.
Article
Cerium oxide based ceramic fuel cells (CFCs) enable a good cell performance with high ionic conductivity when a lithium compound is utilized as the anode material. However, the mechanism of enhancement of the ionic conductivity and its effect on the fuel cell performance as well as the stability involved via the lithium effect have not been fully understood in this stage. In this paper, the role of lithium was unveiled through experimental measurements and DFT calculations in cerium oxide-based CFCs. It is found that the redistribution of lithium in cerium oxide causes gradient Li+ distribution, resulting in the diffusion of Li+ in CeO2 electrolyte to improve the cell performance. Further study discloses that the lithium at the anode is depleted and in situ doped into the cerium oxide lattice, modulating the band structure of CeO2, leading to the increased electronic conductivity and open circuit voltage (OCV) degradation. This work provides an insight into the role of lithium in cerium oxide-based CFCs, opening a new methodology for designing high performance CFCs.
Article
In this study, cost-effective cathode materials with high catalysis activity for oxygen reduction reaction (ORR) are proposed for use in intermediate-temperature solid oxide fuel cells. Cobalt-free Ba0.5A0.5Fe0.8Zr0.2O3-δ (A=Sr²⁺/Sm³⁺, BSrFZ/BSmFZ) composites were synthesised using a smart self-assembled method that primarily utilised doped-BaZrO3 and doped-BaFeO3 cubic perovskites. The BSrFZ composite possesses a higher doped-BaFeO3 (75 wt%) content, which facilitates the formation of oxygen vacancies and ORR catalysis. The BSmFZ composite exhibits a relatively higher content of doped-BaZrO3 (31 wt%) than that of the BSrFZ composite, which is more suited to the electrolyte and improves the thermal expansion coefficient (16.0 × 10⁻⁶ K⁻¹). Both composite cathodes exhibit nano- and micro-particles with extensive heterointerfaces and excellent cathode|electrolyte interfaces, which can assist the surface catalysis and oxygen species transport. The cell with a BSrFZ composite cathode achieved a higher maximum power density of 1.64 W cm⁻² at 750 °C compared to that of the cell with a BSmFZ composite cathode that had a maximum power density of 0.99 W cm⁻². The electrochemical analysis revealed that the BSrFZ composite cathode demonstrated enhanced oxygen adsorption dissociation and oxygen species reduction processes, which benefit from its enriched oxygen vacancies and high surface and heterointerface activities.
Article
A crucial requirement for environmental protection is the removal of carcinogenic organic pollutants from industrial effluents that are discharged into water bodies and jeopardize human health. In this study, newly designed Nd0.7Ca0.3Mn1-xNixO3 (x = 0.01–0.03) perovskite nanocomposites are proposed for the efficient photocatalytic degradation of methylene blue (MB) and tetracycline (TC) organic pollutants. Structural characterization by X-ray diffraction analysis has confirmed formation of a perovskite orthorhombic phase (Pnma) in equilibrium with an Nd2O3 secondary phase, the amount of which reduces significantly from 28 wt% for NdMnO3 to 5 wt% for the highly doped Nd0.7Ca0.3Mn0.97Ni0.03O3. Transmission electron microscopy observation has revealed polygon-shaped particles in the size range 32–56 nm. The band-gap energy was found to gradually decrease from 3.00 to 2.30 eV with increasing Ni loading. The as-prepared composites exhibit paramagnetic behavior, irrespective of the chemical composition, which facilitates simple magnetic recovery. Among the studied nanocomposites, Nd0.7Ca0.3Mn0.97Ni0.03O3 displayed the optimum photocatalytic activities for the degradation of MB (96.0%) and TC (96.6%). Its significantly enhanced photocatalytic activity can be attributed to a combination of several intrinsic characteristics, including high lattice distortion, narrow band-gap energy, a reduced electron–hole recombination rate, increased surface oxygen adsorption, and the presence of spin-polarized bands, as well as synergistic effects due to Ca/Nd substitution and Ni/Mn doping. The degradation reaction follows pseudo-first-order kinetics. Furthermore, the catalyst degrades the studied organic pollutants by at least 95%, with good stability over five consecutive reaction cycles and facile recovery without tedious purification or work-up processes. The present study demonstrates that the as-fabricated perovskite nanocomposite possesses the requisite properties for use as an efficient photocatalyst for the degradation of organic pollutants.
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Gadolinium-doped ceria (GDC) nanopowders, prepared using the co-precipitation synthesis method, were applied as a starting material to form ceria-based thin films using the electron-beam technique. The scanning electron microscopy (SEM )analysis of the pressed ceramic pellets’ cross-sectional views showed a dense structure with no visible defects, pores, or cracks. The AC impedance spectroscopy showed an increase in the total ionic conductivity of the ceramic pellets with an increase in the concentration of Gd2O3 in GDC. The highest total ionic conductivity was obtained for Gd0.1Ce0.9O2-δ (σtotal is 11 × 10−3 S∙cm−1 at 600 °C), with activation energies of 0.85 and 0.67 eV in both the low- and high-temperature ranges, respectively. The results of the X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma optical emission spectrometer (ICP-OES) measurements revealed that the stoichiometry for the evaporated thin films differs, on average, by ~28% compared to the target material. The heat-treatment of the GDC thin films at 600 °C, 700 °C, 800 °C, and 900 °C for 1 h in the air had a minor effect on the surface roughness and the morphology. The results of Raman spectroscopy confirmed the improvement of the crystallinity for the corresponding thin films. The optimum heat-treating temperature for thin films does not exceed 800 °C.
Article
We herein report an impedance spectroscopy study of Au electrodes on Gd-doped CeO2 (GDC) – molten Li2CO3+Na2CO3 (LNC) composite electrolytes in O2 and O2+CO2 atmospheres. Complementary measurements of Au on GDC alone are provided for supporting insight. We find that the adsorption of CO2 on GDC in O2+CO2 atmospheres effectively blocks oxygen adsorption and severely slows oxygen reduction kinetics. The conductivity of the composite is dominated by the GDC phase in the solid-solid temperature region, while the LNC phase dominates above its melting point, and no further enhancement e.g. by interfacial effects are found. The incorporation of LNC melt into GDC results in a significant reduction in the polarisation resistance of Au electrodes in O2 atmospheres, as the melt mediates the reaction by a peroxide mechanism. In O2+CO2 atmospheres, however, the polarisation resistance of Au electrodes on GDC-LNC membranes is significantly higher, higher even than that on GDC. This we assign again to the blocking adsorption of CO2 (or carbonate) on the surfaces of ceria and the sluggish transport and reactions now mediated by carbonate-carried oxide species (CO4²⁻) instead of peroxide species.
Article
In this study, we synthesize Li13.9Sr0.1Zn(GeO4)4 (LSZG) electrolyte materials using the sol-gel method. The x-ray powder diffraction results indicate that the pure LSZG material was successfully obtained using the sol-gel method. The scanning electron microscopy (SEM) results show that, unlike LSZG-SS (solid-state) powder, LSZG-SG (sol-gel) powder has smaller size, which promotes sintering and reduces the sintering temperature. In addition, it is verified that LSZG electrolyte can conduct Li⁺/H⁺ ion exchange in a humid H⁺ environment. Unlike the LSZG-SS sample, the LSZG-SG electrolyte can promote the Li⁺/H⁺ ion exchange and has a higher proton conductivity. The BaZr0.4Ce0.4Y0.1Ni0.1O3 barrier layer coated on the surface of LSZG pellets can inhibit lithium-ion conduction, making the protons the only mobile ion. The proton conductivity of LSZG-SG electrolyte with a barrier layer is approximately 0.035 S/cm at 600 °C. Furthermore, solid oxide fuel cells based on LSZG-SG electrolyte has an open-circuit voltage of 1.0 V and a maximum power density of 17 mW cm⁻² at 600 °C.
Article
This present work reports the facile sol-gel synthesis of Y³⁺ doped Ba(Ce,Zr)O3 with composition of BaCe0.54Zr0.36Y0.10O2.95 (BCZY). Series of six samples were prepared using various chelating agents namely citric acid (denoted as S1, 210 g/mol), tartaric acid (S2, 150 g/mol), glycolic acid (S3, 70 g/mol), nitriloacetic acid (S4, 191 g/mol), ethylenediaminetetraacetic acid (S5, 292 g/mol) and triethylenetetramine (TETA) (S6, 146 g/mol). The influence of chelating agents’ molecular weight (Mw) and functional group on thermal decomposition, phase formation and morphology of BCZY were explored. The reaction products obtained after heat treatment were characterized by Thermal Gravimetric Analyzer (TGA), Fourier Transform Infrared (FTIR) spectrometer, X-ray diffractometer (XRD) and Scanning Electron Microscope (SEM) equipped with Energy Dispersive X-ray (EDX) spectrometer. TGA along with FTIR analysis confirmed that the thermal decomposition of all samples achieved almost completion at processing temperature below 1000 °C. TGA verified the weight loss of intermediate compounds increased with an increase in the Mw of the chelating agents in the following trend: S3 (28%) < S6 (35%) < S2 (40%) < S4 (90%) < S1 (93%) < S5 (95%). At calcination temperature of 1100 ° C, XRD pattern of all samples excluding S4 showed successful formation of single-phase BCZY crystals. The highest percentage (99.5%) of BCZY perovskite phase was achieved for S6. In contrast, S4 exhibited 57.5% secondary phase of BaCeO3 and 42.5% BCZY, suggesting incomplete formation of the required perovskite phase. SEM revealed all calcined powders have similar morphology of clump-like network structure. The use of different types of chelating agents interacts with different atomic radius of metal cations resulted in the formation of Zr-cluster and Ce-cluster, suggesting the possible cause for the fluctuations observed in the EDX elemental composition of the calcined powders.
Chapter
A fuel cell is an electrochemical device that converts chemical energy to electrical energy by an electrochemical reaction of fuel and oxidative agents. Fuel cells are potential future cleaner energy sources and an alternative instrument of an internal combustion engine (ICE). Fuel cells are having three main parts: Cathode, anode, and electrolyte. The role of polymer electrolytes in the fuel cell is the transportation of ions from one electrode to another electrode. Depending on the electrolyte material used, the fuel cell can be classified as polymer electrolyte fuel cells, solid oxide fuel cells, alkaline fuel cells, phosphoric acid fuel cells, Molten Carbonate Fuel Cells. This encyclopedia article focuses on various types of polymer used as membranes, i.e., the electrolyte in polymer electrolyte fuel cells, including their physical, chemical properties, performance in fuel cells. The copolymer of tetrafluoroethylene based plastics materials is the most commercially used plastic for the preparation of membrane in fuel cells applications because of its excellent mechanical strength, and chemical stability, high conductivity, long durability, but it exhibited some limitations such as low conductivity in anhydrous condition, poor fuel cell performance at high temperature. Acid doped-polybenzimidazole (PBI) is another type of engineering plastic that many researchers have explored for fuel cell applications because of its excellent performance in fuel cells like: high thermal stability, good chemical resistance, superior mechanical strength, high ion conductivity. Besides, the operating temperatures of acid doped-polybenzimidazole (PBI) based fuel cells were found to be considerably higher (~200°C) compared to tetrafluoroethylene-based fuel cells. There are few more engineering plastics such as, poly(ether ether ketone) (PEEK), polystyrene (PS), polysulfone (PSF), polyimide (PI) etc. were also investigated as the membrane in fuel cells.
Chapter
As SOFCs mainly consist of low cost ceramic oxide and metallic materials, the processing and fabrication techniques play an critical role in the overall cost of SOFC technologies. In this Chapter, various powder synthesis, dense and porous coating and film fabrication methods and multiple layer structure depositon techniques in SOFCs will be introduced. This is followed by the discussion of sintering and polarization induced interface formation and latest development in the nano-scale structure in SOFCs.
Article
This work reports the preparation of nanocrystalline Ni-Gd0.1Ce0.9O1.95 (NiO-GDC) anode powders using a novel single-step co-precipitation synthesis method (carboxylate route) based on ammonium tartrate as a low-cost green precipitant. The thermogravimetric analysis (TGA) of the synthesised powder showed the complete calcination/crystallisation of the resultant precipitates to take place at 500 °C. The prepared NiO-GDC powder was coated on a GDC electrolyte disc and co-sintered at 1300 °C. A mixture of La0.6Sr0.4Co0.2Fe0.8O3−δ and GDC was used as the cathode material and subsequently coated onto the anode-electrolyte bilayer, resulting in the fabrication of a NiO-GDC|GDC|La0.6Sr0.4Co0.2Fe0.8O3−δ-GDC cell. The crystallite size of both NiO and CeO2 phases were estimated using the X-ray powder diffraction (XRD) profiles and were calculated to be ∼14 nm. Applied H2 temperature-programmed reduction (H2-TPR) analysis indicated a synergetic effect among different anode composites' constituents, where an intense interaction between the dispersed NiO nanocrystalline particles and the GDC crystallite phase had weakened the metal-oxygen bonds in the synthesised anode composites, resulting in a strikingly high catalytic activity at temperatures as low as 300 °C. The electrochemical impedance spectroscopy (EIS) and the electrochemical performance of the fabricated cells were measured over a broad range of operating temperatures (500–750 °C) and H2/Ar-ratios of the anode fuel (e.g. 100%–15%). Quantitative analysis from the EIS data and the application of the distribution of relaxation times (DRT) method allowed for the estimation of the activation energies of the anodic high and intermediate frequency processes that were 0.45 eV and 0.76 eV, respectively. This is the first report of a NiO-GDC synthesis, where a considerable improvement in activation energy is observed at the low-temperature region. Such low activation energies were later associated with the adsorption/desorption process of water molecules at the surface of NiO-GDC composite, indicating a high activity towards hydrogen oxidation.
Article
Cracks and delamination primarily revealed in the microscale‐thick cathode have been known as the major cause of increasing the polarization resistance and inhibiting the low‐temperature operation of solid oxide fuel cells (SOFCs). Besides, these defects were originated from the polymer dispersant, essential for the fabrication of the bulk cathode layer. Herein, we manufactured a crack‐free cathode layer by optimizing the deposition temperature (Tdep) of the powder‐suspension electrospray deposition (ESD) process through thermal characterization of polyvinylpyrrolidone (PVP), a polymer used in the slurry of ESD. SOFCs with the cathode deposited at the glass transition temperature of PVP resulted in a maximum power density of 0.481 W cm−2, 37 and 39% improved than those with the cathode deposited at Tdep = 25 and 200 ℃, respectively, at 650 ℃. Furthermore, the effect of uniformly dispersed morphology of cathode without defects was demonstrated by the reduction of polarization resistance through electrochemical impedance spectroscopy analysis. This article is protected by copyright. All rights reserved
Article
Recent studies have realized fast ionic transport in pure ceria (CeO2) via surface conduction without using conventional structural doping, indicating a promising strategy to develop electrolytes for low-temperature solid oxide fuel cells (LT-SOFCs). In this work, to further develop the potential of non-doped ceria, a new CeO2 electrolyte (CeO2#1) is synthesized through precipitation method by using Na2CO3 as precipitant for surface modification, and compared with two other CeO2 samples (CeO2#2 and CeO2#3) prepared by NH4HCO3 and KOH precipitants. The CeO2#1 is found to be composed of ceria and slight amorphous Na2CO3, while CeO2#2 and CeO2#3 contain simplex ceria. When applied in SOFCs, the CeO2#1 electrolyte achieves attractive fuel cell performance (706 mW cm−2 at 550 °C) with good stability, demonstrably superior to those of CeO2#2 and CeO2#3 electrolytes. Further impedance spectra analysis manifests the high proton conductivity of CeO2#1, and suggests that the electrochemical performance superiority of CeO2#1 should be ascribed to its micro-structural feature. Subsequent TEM characterization confirms the existence of Na2CO3 in CeO2#1 as an ultra-thin coating layer, benefiting from which, the CeO2 can be protected from being reduced by H2 and enable high ionic conductivity by virtue of ceria/carbonate interface. This work thus points out a new type of non-doped ceria electrolytes with different working mechanism from previous studies and indicates a feasible approach to develop high-performing and stable electrolytes for LT-SOFCs.
Article
The thermal stress caused by the interfacial thermal resistance (ITR) between Ni and yttria-stabilized zirconia (YSZ) is one of the major factors causing the destruction of solid oxide fuel cells (SOFCs). However, the complicated chemical reactions occurring in this Ni/YSZ interface make it difficult to study the ITR of Ni/YSZ interface by conventional simulations and experiments. By using the state of art reactive molecular dynamics simulations together with the modification of two-temperature model, ITRs of three typical Ni/YSZ interfaces under hydrogen-free condition and in hydrogen environment are investigated in this paper. The accuracy of the present simulation methods is verified by the transient thermoreflectance experiments. Our simulation results indicate that among different Ni/YSZ interface structures, the Ni[100]/YSZ[100] interface possesses the largest ITR. Moreover, the ITR of Ni/YSZ interfaces is found to increase significantly as the temperature grows from room temperature to the working temperature of SOFCs. In hydrogen environment, a great enhancement is observed in the ITR of Ni/YSZ interfaces after chemical reaction, which becomes more significant as the hydrogen concentration increases. The enhanced ITR observed after chemical reaction mainly originates from the breaking of chemical bonds at Ni/YSZ interfaces and also the enhanced phonon mismatch between Ni and YSZ.
Thesis
Full-text available
Printed electronics have led to new possibilities in the development of low-cost and low-temperature methods for materials production and processing. Inorganic oxide devices that are totally solution-processed offer an appealing approach, overcoming some limitations of organic electronics, such as performance and stability. Solution processes are simple and versatile however, there are still some drawbacks that need to be addressed. Currently, synthesis of these materials usually needs higher temperatures and longer annealing time which limits their use on flexible substrates being crucial for flexible and wearable device applications. In this thesis, a general overview is made to solution combustion synthesis (SCS) method to synthetize nanostructures, thin films and their application in thin film transistors (TFTs) with a low thermal budget.Also, new strategies towards processing of solution-based metaloxide TFTs such as, oxide synthesis, post deposition treatments, low temperature high emerging printing techniques are discussed. Relevant steps to boost solution-based metal oxide TFTs are analysed, since the optimization of metal oxide (MO) thin films processed at low temperature until their printability in Roll-to-Roll (R2R) compatible techniques. To go even further some tests are performed to decrease the processing time required for the formation of MO thin films. To finalize, special attention is given to solution-based metal oxide resistive switching devices in which the resistive states are quite important to represent different logic states (e.g. binary code) being useful for many digital applications.
Article
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A modified Pechini process is successfully developed for preparation of lanthanum strontium doped manganites thin films. In order to understand the mechanisms of gel formation, correlations are established between viscosity-which is the key parameter-and film thickness. The correlation between the latter and metal salts concentration is also shown. These gels are deposited on yttria stabilized zirconia (YSZ) substrates by dip-coating. Experimental parameters are optimized to get stable solutions (which yield materials with reduced crystallization temperatures). When the solution is heated to remove part of solvents, an intermediate resin forms. This resin deposited on substrates is heated to elevated temperatures. During the calcination step, organic residuals are removed and oxide compounds are elaborated. It involves exothermic decomposition and it requires an optimization of thermal treatment to keep films crack-free and homogeneous. Then, mono or multi layer thin films of La 1-xSr xMnO 3+δ are synthesized. They present various morphologies and primary particles size distributions. This method allows us to obtain a 250 nm thick monolayers film and even thicker films for multilayers. The porosity of films appears to change according to heat treatment.
Article
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A review dealing with the use of screen-printing technology to manufacture disposable electrodes is presented, covering in details virtually all the publications in the area up to early 1997 and including 206 references. The elements and different strategies on constructing modified electrodes are highlighted. Commercial and Home-made ink recipes are discussed. Microelectrode arrays, built by the combination of photostructuring and screen-printing technologies to the mass production of advanced disposable sensors, are also discussed. Future research trends are predicted.
Article
Full-text available
In this paper the current status of fuel cells is described with particular emphasis on high (T > 800 ºC) and intermediate (T < 800 ºC) temperature solid oxide fuel cells. Also the importance of the fuel cell technology is shown. Reviewed are the fundamental features, the basic principles, types of fuel cell, fabrication methods, cell configurations and the development of components (cathodes, anodes, electrolytes, interconnect) and materials.
Article
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Perovskite-oxide nanocrystals of La0.75Sr0.25Cr0.93Ru0.07O3–δ with a mean size around 10 nm were prepared by microwave flash synthesis. This reaction was performed in alcoholic solution using metallic salts, sodium ethoxide and microwave autoclave. The obtained powder was characterised after purification by energy dispersive X-ray analysis (EDX), X-ray powder diffraction (XRD), BET adsorption technique, photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM). The results show that integrated perovskite-type phase and uniform particle size were obtained in the microwave treated samples. At last the synthesised powder was directly used in a sintering process. A porous solid, in accordance with the expected applications, was then obtained at low sintering temperature (1000 °C) without use of pore forming agent.
Article
The four components of portland cement-dicalcium silicate, C2S (Ca2SiO4); tricalcium silicate, C3S (Ca3SiO5); tricalcium aluminate, C(3)A (Ca3Al2O6); and tetracalcium aluminate iron oxide, C(4)AF (Ca4Al2Fe3O10)-were formed using a solution-polymerization route based on poly(vinyl alcohol) (PVA) as the polymer carrier. The powders were characterized using X-ray diffraction techniques, BET specific surface area measurements, and scanning electron microscopy, This method produced relatively pure, synthetic cement components of submicrometer or nanometer crystallite dimensions, high specific surface areas, as well as extremely high reactivity at relatively low calcining temperatures. The PVA content and its degree of polymerization had a significant influence on the homogeneity of the final powders; Two types of degree of polymerization (DP) PVA were used. Lower crystallization temperatures and smaller particle size powders were obtained from the low-DP-type PVA at optimum content.
Article
The single-phase, cubic-perovskite region of the LaO1.5-SrO-Gao(1.5)-MgO phase diagram was determined from room-temperature and high-temperature X-ray diffraction. Two impurity phases were identified, LaSrGaO4 and LaSrGa3O7. The conductivity of the oxygen-deficient perovskite phase was shown to be essentially a purely oxide-ion conductivity sigma(o) over a wide range of oxygen partial pressures 10(-22) less than or equal to P-O2 less than or equal to 1 atm, The highest values of sigma(o) = 0.17 and 0.08 S/cm were found for La0.8Sr0.2Ga0.83Mg0.17O0.2815 at 800 degrees and 700 degrees C, respectively; they remain stable over a week-long test. The Arrhenius plot of sigma(o) is curved, dividing into a high-temperature region T > T* approximate to 600 degrees C and a low-temperature region T < T*. Above T* all the oxygen vacancies appear to be mobile; below T* they progressively condense into clusters of ordered vacancies.
Article
This work is focused on the comparative analysis of electrochemical and transport properties in the major families of cathode and anode compositions for intermediate-temperature solid oxide fuel cells (SOFCs) and materials science-related factors affecting electrode performance. The first part presents a brief overview of the electrochemical and chemical reactions in SOFCs, specific rate-determining steps of the electrode processes, solid oxide electrolyte ceramics, and effects of partial oxygen ionic and electronic conductivities in the SOFC components. The aspects associated with materials compatibility, thermal expansion, stability, and electrocatalytic behavior are also briefly discussed. Primary attention is centered on the experimental data and approaches reported during the last 10-15 years, reflecting the main challenges in the field of materials development for the ceramic fuel cells.
Article
The synthesis, characterization, and proposed mechanism of formation of a new family of silicate/aluminosilicate mesoporous molecular sieves designated as M41S is described. MCM-41, one member of this family, exhibits a hexagonal arrangement of uniform mesopores whose dimensions may be engineered in the range of ∼ 15 Å to greater than 100 Å. Other members of this family, including a material exhibiting cubic symmetry, have been synthesized. The larger pore M41S materials typically have surface areas above 700 m2/g and hydrocarbon sorption capacities of 0.7 cc/g and greater. A templating mechanism (liquid crystal templating - LCT) in which surfactant liquid crystal structures serve as organic templates is proposed for the formation of these materials. In support of this templating mechanism, it was demonstrated that the structure and pore dimensions of MCM-41 materials are intimately linked to the properties of the surfactant, including surfactant chain length and solution chemistry. The presence of variable pore size MCM-41, cubic material, and other phases indicates that M41S is an extensive family of materials.
Article
The recent interest in building a decentralized, hydrogen-based energy economy has refocused attention on the solid oxide fuel cell (SOFC) as potential source of efficient, environmentally friendly, fuel-versatile electric power. This review covers the advances made to date in the understanding of SOFC cathodes. Focus is on how new approaches have been used by workers to better understand cathode mechanisms and how these mechanisms relate to materials properties and microstructure.
Article
La 1-xA′ xFe 0.8Co 0.2O 3δ (A′ = Ca, Sr, Ba) perovskite powders were synthesized to attain the desired properties of high O 2 flux and stability under reducing conditions. Steady-state oxygen permeation rates for La 1-xA′ xFe 0.8-Co 0.2O 3-δ perovskite membranes in nonreacting experiments with air on one side and helium on the other side of the membrane were in the order A′ = Ba 0.8 > Ba 0.6 > Ca 0.6 > Sr 0.6. Partial oxidation of methane to syngas (CO + H 2) was performed in a dense La 0.2Ba 0.8Fe 0.8Co 0.2O 3-δ membrane reactor at 850° C in which oxygen was separated from air and simultaneously fed into the methane stream. The reducing atmosphere affected the membrane reaction-side surface while barium enrichment occurred on the air-side surface. Oxygen continuously transported from the air side appeared to stabilize the membrane interior, and the reactor was operated for up to 850 h.
Article
Soft-chemical routes play an important role in preparation of nano-materials. In particular, the combustion synthesis has emerged as a promising solution-chemistry route for synthesizing a variety of oxide ceramics in the nano-crystalline form. In this review article, the potential of this technique for preparation of a few oxide ceramics viz. yttria, barium polytitanates, barium and strontium thorate, strontium cerates powders has been presented. The role of process parameters in controlling the powder characteristics has also been established. These powders were characterized in terms of X-ray diffraction, surface area analysis, electron microscopy and sinterability. This process was shown to be a simple and cost effective, which results in the phase pure, nano-crystalline powders having high surface area and better sinterability. These combustion-synthesized sinter-active powders achieved near the theoretical density, while retaining the fine grain microstructure.
Article
A new and simple chemical route has been used to synthesize mixed-oxide powders. The method uses long-chain polymers, such as poly(vinyl alcohol) and poly(ethylene glycol). The chemistry of the precursor solution differs from other solution-polymerization techniques. The stabilization of the cations in the precursor is established not only through the chemical binding of cations with the functional groups, but also, in major part, through the physical entrapment of the metal ions in the network of the dried polymer carrier. Pure, single-phase calcium aluminate, yttrium aluminate, and yttrium phosphate powders have been produced, while maintaining a 4:1 ratio of positively charged valences of the cations (Men+) to negatively charged hydroxyl (-OH-) groups. The ceramic yield of the new method (the ratio of the weight of the ceramic powders to the weight of the organics that are used in the preparation) is approximately 2.
Article
Ferroelectric ceramics are important electronic materials that have a wide range of industrial and commercial applications, such as high-dielectric constant capacitors, piezoelectric sonar or ultrasonic transducers, pyroelectric security sensors, medical diagnostic transducers, electro-optical light valves, and ultrasonic motors, to name a few. The performances of ferroelectrics are closely related to the ways they are processed. The conventional solid state reaction method requires high calcination and sintering temperatures, resulting in the loss of lead, bismuth or lithium components due to their high volatilities, thus worsening the microstructural and subsequently the electrical properties of the ferroelectric materials. Various wet chemistry based routes have been developed to synthesize ultra-fine and even nano-sized ferroelectric powders. However, most of the chemistry based routes still involve calcinations, although at relatively lower temperatures. High energy mechanochemical milling process has been shown that some ferroelectric materials can be synthesized directly from their oxide precursors in the form of nano-sized powders, without the need for the calcination at intermediate temperatures, thus making the process very simple and cost-effective. A large number of ferroelectric materials, including lead-containing ferroelectrics, antiferroelectrics and relaxors, and bismuth-containing Aurivillius families, have been synthesized by the high-energy milling process. Some ferroelectrics, such as barium titanate (BaTiO3 or BT), lead iron tungstate [Pb(Fe2/3W1/3)O3 or PFW], and several bismuth-containing materials, that cannot be directly produced from their oxide mixtures, have been formed at relatively low temperature after their precursors are activated by an high-energy milling. Ferroelectric ceramics derived from the activated precursors demonstrated better microstructure and electrical properties than those without mechanochemical treatment. This review presents an overview of the recent progress in the synthesis of ferroelectric ceramic powders using various high-energy milling techniques. The progress includes several aspects: (i) direct synthesis of nano-sized powders with better sinterability, (ii) promoted reactive sintering due to the modification of the precursors, (iii) amorphization of the precursors, and (iv) refinement of the precursors with high homogeneity. The underlying mechanisms of mechanochemical synthesis of ferroelectric materials are discussed. Further research emphasizes on issues related to the synthesis of ferroelectric ceramic powders are suggested.
Book
Here some information, quoted from Google Books: "Inorganic Chemistry easily surpasses its competitors in sheer volume and depth of information. Readers are presented with summaries that ease exam preparation, an extensive index, numerous references for further study, six invaluable appendixes, and over 150 tables that provide important data on elements at a quick glance. Now in its 101st printing, Inorganic Chemistry provides an authoritative and comprehensive reference for graduate students, as well as chemists and scientists in fields related to chemistry such as physics, biology, geology, pharmacy, and medicine. Translated for the first time into English, Holleman and Wiberg's book is a bestseller in Germany, where every chemist knows and values it. Prior to this translation, there was no equivalent to Holleman and Wiberg's book in English". Please note that there is no ‘full text’ available. The book was published in 2001 and as far as known, there is no digital version. Also, it is long – 1884 pages – and is still under copyright.
Article
Three solid-oxide fuel cell (SOFC) electrolytes, yttria-stabilized zirconia (YSZ), rare-earth–doped ceria (REDC), and lanthanum strontium gallium magnesium oxide (LSGM), are reviewed on their electrical properties, materials compatibility, and mass transport properties in relation to their use in SOFCs. For the fluorite-type oxides (zirconia and ceria), electrical properties and thermodynamic stability are discussed in relation to their valence stability and the size of the host and dopant ions. Materials compatibility with electrodes is examined in terms of physicochemical features and their relationship to the electrochemical reactions. The application of secondary ion mass spectrometry (SIMS) to detect interface reactivity is demonstrated. The usefulness of doped ceria is discussed as an interlayer to prevent chemical reactions at the electrode–electrolyte interfaces and also as an oxide component in Ni–cermet anodes to avoid carbon deposition on nickel surfaces. Finally, the importance of cation diffusivity in LSGM is discussed, with an emphasis on the grain-boundary effects.
Article
The wet powder spraying (WPS) technique was used for the deposition of dense and thin (Y2O3)0.08(ZrO2)0.92 (YSZ-8) films on an anode substrate being used for fuel cell applications. Both agglomeration of the powder and the presence of organics in the substrate have a significant effect on the quality and densification of the thin electrolyte layer. High-energy ball milling effectively broke up the agglomerates and enhanced the packing density of the green layer. Pre-calcination of the substrate at ∼1000 °C enhanced the match of sintering shrinkage between the electrolyte layer and the substrate and improved the quality of the YSZ-8 thin film significantly. Crack-free dual-layer assembly with a highly densified YSZ-8 film as thin as 10 μm was successfully fabricated by optimizing the fabrication parameters. The cells with a La0.8Sr0.2MnO3 cathode showed a high open circuit voltage of 1.071 V and a peak power density of 894 mW cm−2 at 850 °C operated with hydrogen fuel.
Article
In order to lower the raw materials cost and develop a novel cathode materials for intermediate temperature solid oxide fuel cell(ITSOFC), using mixed rare earth replacing the expensive pure La2O3 as the raw materials, the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ(Ln = the mixed rare earth, x = 0.05, 0.10, 0.15) for the applications as the cathode materials were prepared by microwave sintering process. The crystal structure and the particles morphology of the obtained powders were characterized by XRD and SEM, the electrical conductivity of all samples sintered at 1200 °C for 3 h was also measured as the function of the temperature from 100 to 800 °C by DC four-probe method in air. The experimental results show that due to the influence of mixed rare earth the powders of Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ synthesized at 1200 °C for 0.5 h with the mean particle size of 1 ∼ 20 μm was of perovskite and cubic fluorite phase as well a little SrO phase, the electrical conductivity of the samples decreases with the adding Ca2+ content, and are all higher than 100 S·cm−1 from 500 to 700 °C when x≤0.10. Ln0.7Sr0.3-xCaxCo0.9Fe0.1O3-δ. can meet the demand of the electrical properties for the cathode materials in ITSOFC.
Article
BaCe0.8Sm0.1Gd0.1O3−δ, a material for an electrolyte of solid oxide fuel cells, was prepared by a newly sol-combustion method to obtain fine grain size and good sinterability. The phase formation, sinterability and electrical conductivity were focused on by this study. The results show that nano-sized BaCe0.8Sm0.1Gd0.1O3−δ powders with single orthorhombic perovskite structure were prepared by this process successfully. The powders showed high sinterability, and a relative of 95.2% of the theoretical density was obtained at a sintering temperature of 1400 °C. Electrochemistry measurements showed that the BaCe0.8Sm0.1Gd0.1O3−δ ceramics had relatively high oxygen ionic conductivity in low-temperature range.
Article
This paper reports on the synthesis of 20 mol% Gd2O3-doped CeO2 solid solution (20 GDC) nano-particles via carbonate co-precipitation. Precursors and calcined particles were characterized using TGA, XRD, BET, FESEM, and TEM. From the diffraction pattern using XRD with TEM, it was shown that the Gd3+ replaced the Ce4+ lattice in the fluorite structure (FCC) of CeO2, as opposed to it being a second phase in the CeO2 structure. The 20 GDC particles were calcined at 700 °C for 2 h, and sintered to >99% density at a very low sintering temperature of 1150 °C for 4 h.
Article
(La0.75Sr0.25)0.95MnO3±δ (LSM) powders have been synthesized via a Pechini route. The prepared powders were characterized by XRD, SEM, XRF, BET and particle size distribution (PSD) analysis. It is shown that the morphology and structure of the oxide particles are significantly dependent on the preparation conditions such as the sort of surfactant and pH value of the starting solution. High purity, single phase, homogeneous, nanocrystalline LSM powders with slight aggregation were obtained using citric acid as complexing agent, ethylene glycol as surfactant and pH 1. The conductivity of the sintered LSM sample prepared from this nanocrystalline powders was mensurated about 200 S cm−1 in air at 600–1000 °C. The impedance spectra of symmetric cells LSM–YSZ/YSZ/LSM–YSZ were measured in air and open circuit voltage condition. The optimal polarization resistance (Rp) of 0.175 Ω cm2 at 750 °C and 0.07 Ω cm2 at 800 °C was obtained in the sample with LSM to YSZ weight ratio of 49:51.
Article
A range of La0.75Sr0.25Cr0.5Mn0.5O3−δ (LSCM) powders is prepared by the carbonate coprecipitation method for use as anodes in solid oxide fuel cells. The supersaturation ratio (R = [(NH4)2CO3]/([La3+] + [Sr2+] + [Cr3+] + [Mn2+])) during the coprecipitation determines the relative compositions of La, Sr, Cr, and Mn. The composition of the precursor approaches the stoichiometric one at the supersaturation range of 4 ≤ R ≤ 12.5, whereas Sr and Mn components are deficient at R < 4 and excessive at R = 25. The fine and phase-pure LSCM powders are prepared by heat treatment at very low temperature (1000 °C) at R = 7.5 and 12.5. By contrast, the solid-state reaction requires a higher heat-treatment temperature (1400 °C). The catalytic activity of the LSCM electrodes is enhanced by using carbonate-derived powders to manipulate the electrode microstructures.
Article
Intermediate temperature solid oxide fuel cell cathode materials (Ba, Sr)CoxFe1−xO3−δ [x = 0.2–0.8] (BSCF), were synthesized by a glycine-nitrate process (GNP) using Ba(NO3)2, Sr(NO3)2, Co(NO3)2·6H2O, and Fe(NO3)3·9H2O as starting materials and glycine as an oxidizer and fuel. Electrolyte-supported symmetric BSCF/GDC/ScSZ/GDC/BSCF cells consisting of porous BSCF electrodes, a GDC buffer layer, and a ScSZ electrolyte were fabricated by a screen printing technique, and the electrochemical performance of the BSCF cathode was investigated at intermediate temperatures (500–700 °C) using AC impedance spectroscopy. Crystallization behavior was found to depend on the pH value of the precursor solution. A highly acidic precursor solution increased the single phase perovskite formation temperature. In the case of using a precursor solution with pH 2, a single perovskite phase was obtained at 1000 °C. The thermal expansion coefficient of BSCF was gradually increased from 24 × 10−6 K−1 for BSCF (x = 0.2) to 31 × 10−6 K−1 (400–1000 °C) for BSCF (x = 0.8), which resulted in peeling-off of the cathode from the GDC/ScSZ electrolyte. Only the BSCF (x = 0.2) cathode showed good adhesion to the GDC/ScSZ electrolyte and low polarization resistance. The area specific resistance (ASR) of the BSCF (x = 0.2) cathode was 0.183 Ω cm2 at 600 °C. The ASR of other BSCF (x = 0.4, 0.6, and 0.8) cathodes, however, was much higher than that of BSCF (x = 0.2).
Article
Ce1−xSmxO2−1/2x nanopowders were successfully synthesized by microwave-induced combustion process. For the preparation, cerium(III) nitrate hexahydrate, samarium(III) nitrate hexahydrate, and urea were used for the microwave-induced combustion process. The process took only a few minutes to obtain Ce1−xSmxO2−1/2x powders. Ce1−xSmxO2−1/2x ceramics prepared by microwave-induced process sintered at 1400 °C for 3 h, the bulk density of Ce1−xSmxO2−1/2x ceramics were over 95% of the theoretical density. The results revealed that Ce0.84Sm0.16O1.92 possessed the maximum electrical conductivity was 0.0287 S cm−1 at 850 °C and the minimum activity energy, Ea was 0.9565 eV determined from 500 to 850 °C.
Article
A new method, called the microwave-induced solution-polymerization synthesis (denoted as MW), and the conventional Pechini (denoted as PH) method have been used to prepare powders of La0.8Sr0.2Ga0.83Mg0.17O2.815 (denoted as LS0.2GM0.17) and La0.8Sr0.2(Ga0.9Co0.1)0.83Mg0.17O2.815 (denoted as LS0.2GCM0.17). A higher heating rate and a more homogenous heating manner without thermal gradients in the microwave oven resulted in a pure LSGCM powder after calcination at 1400 °C for 9 hours (h) and purer LSGM (6.2% secondary phases). The grain size of the pellets of the above two powders was 2–3 μm without segregation. The densities of LS0.2GM0.17/MW and LS0.2GCM0.17/MW pellets, sintered at 1400 °C for 9 h, were 6.45 and 6.30 g cm−3, respectively.
Article
A reactive powder of La0.84Sr0.16MnO3 is synthesized as a cathode material for solid oxide fuel cells by a citrate–nitrate auto-ignition process and characterized by thermal analysis, X-ray diffraction and electrical conductivity measurements. The effect of starting metal ion concentration in the precursor solution on the properties of the final oxide is studied and correlated through particle size analyses, sintering studies and microstructural examination. Sintered La0.84Sr0.16MnO3 ceramics of relative density around 93% can be fabricated by preferably keeping the metal ion concentration in the precursor to less than 0.8 M, whereas to make porous ceramics (relative densities of 75–80%) a higher metal ion concentration is preferred. At 1000 °C, the 93% dense ceramics exhibit electrical conductivities of around 168–169 S cm−1 and the porous ceramics of around 136–146 S cm−1.
Article
A number of studies have been conducted concerning compositional/microstructural modifications of a Sr-doped lanthanum ferrite (LSF) cathode and protective Sm-doped ceria (SDC) layer in an anode supported solid oxide fuel cell (SOFC). Emphasis was placed on achieving enhanced low temperature (700–800 °C) performance, and long-term cell stability. Investigations involved manipulation of the lanthanum ferrite chemistry, addition of noble metal oxygen reduction catalysts, incorporation of active cathode layer compositions containing Co, Fe and higher Sr contents, and attempts to optimize the ceria barrier layer between the LSF cathode and YSZ electrolyte.
Article
The dissolution of divalent cations plays an important role in the enhancement of conductivity for perovskite-based LaAlO3 and LaGaO3 oxygen conductors. In the LaAlO3 system, the solubility of MgO was less than 10% due to the mismatch of ionic radius between the Mg and Al cations. The substitution of Sr ions in the La-cation sublattice was as high as 20%. With the doubly-doping of SrO and MgO in LaAlO3, the enhancement of MgO solubility was also observed. However, further addition of MgO tends to lower the solubility of Sr ion from 20 to 10%. This result can be rationalized by the reduced distance between Mg ion and Sr ion that caused the cation–cation repulsion in the perovskite structure. In the singly-doped LaGaO3 systems, the solubility of MgO was found to be 20%. However, only less than 10% of the La-cation sublattice could be substituted by Sr ions. With the doubly-doping of SrO and MgO, the solubility of SrO was significantly enhanced by the addition of MgO. It is believed that the solubility enhancement of SrO is due to the expanded lattice caused by the addition of MgO. Within the solubility limit of the aliovalent cations, the ionic conductivities of both LaAlO3 and LaGaO3 systems increased with the increasing concentration of foreign cations. After the solubility limits in both doped LaAlO3 and LaGaO3 were reached, the segregation of the second phase tends to lower the ionic conductivity drastically. The activation energy for ionic conduction was also dependent on the ionic radius of foreign cations which may affect the space available for the transport of oxygen ions.
Article
Pure and Sr-doped LaGaO3, LaFeO3 and LaCoO3 and Sr,Mg-doped LaGaO3 were synthesized by various wet chemical routes, namely combustion, co-precipitation and citrate-gel methods. The effect of the various process parameters on the phase purity, particle size and surface area and morphology of the synthesized powders were determined by XRD, simultaneous TG-DTA, laser light scattering, BET and scanning electron microscopy. The stability of the synthesized pure phases in oxidizing and reducing atmosphere was also studied by thermogravimetry. It was observed that pure and Sr-doped single perovskite phases of lanthanum ferrite, cobaltite and gallate and Sr,Mg-doped lanthanum gallate could be synthesized by combustion and citrate-gel methods under suitable process conditions. Synthesis using the co-precipitation method yielded incomplete reaction irrespective of the calcination temperature adopted. The citrate-gel method yielded better powder properties in terms of particle size and morphology and surface area compared to combustion synthesis. It was found that pure and Sr-doped lanthanum ferrite, lanthanum cobaltite, lanthanum gallate and Sr,Mg-doped lanthanum gallate were stable in the oxidizing atmosphere. In the reducing atmosphere, pure and Sr-doped lanthanum ferrite and Sr,Mg-doped lanthanum gallate was found to be stable at least during the timeframe of the thermogravimetric experiment whereas pure and Sr-doped lanthanum cobaltite was partially reduced in hydrogen atmosphere.
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Nanocrystalline calcium-doped ceria powders for solid electrolyte ceramics were successfully prepared via a nitrate–citrate combustion route. The effect of ignition temperature on the characteristics of the powders were discussed. XRD indicated that a pure fluorite phase was formed at 160 °C. Using these powders, highly dense ceramics were prepared by sintering at much lower temperatures than 1700 °C, common for ceria solid electrolytes preparation by conventional ceramic techniques. The change of the crystal structure and electric conductivity with the content of doped Ca were also investigated.
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La1−xSrxCoO3 (LSC, x=0.10–0.50) powders with pure perovskite structure have been synthesized from mixtures of La2O3, SrCO3, and Co3O4, irradiated in a domestic microwave oven (DMO) with 2.4.5 GHz and 700–800 W output for no more than 25 min. It is found that Co3O4 couples with microwave well and raises its temperature greatly within 3 min, while neither La2O3 nor SrCO3 absorbs microwave energy at the ordinary temperature. The microwave synthesizing conditions depend on the Sr2+ replacement amount, and get difficult when x is high. The traditional solid state reaction method is compared to treat the same mixtures. It appears that the pure phases of LSC cannot be obtained until 1100–1200°C for 4 h. The lower temperature and shorter time with microwave irradiation might be ascribed to the activating and facilitating effect of microwave on solid phase diffusion. The LSC powders made by the microwave process were screen-printed onto compact yttrium-doped ceria (YDC) pellets, the common electrolyte for solid oxide fuel cells (SOFC), to observe the interaction between them. SEM photograph shows that LSC film has good sintering and porous properties, and fair compatibility with YDC. Thus, microwave irradiation is proved to be a novel, extremely facile, time-saving and energy-efficient route to the synthesis of LSC powders.
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The structure, thermal expansion and ionic conductivity of solid electrolytes based on samarium doped cerium oxide, Ce1−xSmxO2− (x = 0−0.30), prepared by the sol-gel method were systematically investigated in a wide range of temperature of 200–650 °C. The uniformly small particle size of the sol-gel prepared materials allows sintering of the samples into highly dense ceramic pellets at significantly lower temperature 1400 °C compared to that of 1600 °C required for samples prepared by solid state techniques. The ionic conductivity increases with increasing samarium substitution and reaches a maximum for the composition Ce0.80Sm0.20O1.9 (~5 × 10−3 S cm−1 at 600 °C). Thermal expansion coefficients range between 8–10 × 10−6 K−1.