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Anode Supported Solid Oxide Fuel Cells with Screen-Printed Cathodes
Abstract
To increase power density at reduced temperature operation of SOFC, thin film 8YSZ electrolytes were deposited on Ni–YSZ anode support plates by tape casting and cofiring. Cathode behaviour, limiting cell output at lower temperature, was studied in more detail. Cathodes were deposited by screenprinting and firing. With consecutive layers of doped lanthanum manganite and cobaltite, power density of 0.5 W cm−2 at 750°C was obtained using hydrogen fuel. On cells of 100 cm2, no fuel diffusion limitation above 70% conversion occurred, and electrical efficiency of 35% was achieved. Actual cell temperature increases significantly above a current density of 0.3 A cm−2. This effect causes erroneous electrode and cell characteristics.
... Figure 8 shows the EIS plots of the single cells operated with wet H2 (~3% H2O) as fuel and flowing air as the oxidant. The polarization resistance (Rp) of a single cell mainly comes from the cathode and anode, but the Rp value of the anode is negligible when wet H2 (~3% H2O) is used as fuel [46,47]. Therefore, the Rp values of the single cell predominantly correspond to the cathode side. ...
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.
... In both cases, the LSM oxygen electrodes were completely delaminated from the YSZ electrolyte. The abnormal overpotential change of the electrodes after the polarization at 50 mA cm À2 for 16 h and 200 mA cm À2 for 1 h ( Fig. 1c and d) could be caused by the electrode delamination or the excess Joule heat and thereby the rise of local temperature due to the large ohmic resistance [42]. i n t e r n a t i o n a l j o u r n a l o f h y d r o g e n e n e r g y x x x ( 2 0 1 5 ) 1 e1 3 Fig. 2 shows the impedance responses of LSM oxygen electrodes during the anodic polarization in the absence and presence of borosilicate glass. ...
The effect of boron species from borosilicate glass sealant on the electrocatalytic activity and microstructure of La0.8Sr0.2MnO3 (LSM) oxygen electrodes is studied for the first time under accelerated solid oxide electrolysis cell (SOEC) operation conditions at 800 °C. The presence of volatile boron species has remarkable detrimental effect on the electrochemical activity of LSM oxygen electrode for the O2 evolution reaction (OER). After polarization at 200 mA cm−2 for 2 h, the electrode polarization and ohmic resistances increase rapidly from ∼40 and 1.2 Ω cm2 to 614 and 33 Ω cm2, respectively. Under the anodic polarization conditions, there is an accelerated Sr segregation and boron deposition preferentially occurs at the electrode/electrolyte interface, forming lanthanum borates and manganese oxide. Boron deposition and reaction is driven to the interface region due to the increased activity and energetics of lanthanum at LSM lattice sites at the electrode/electrolyte interface under anodic polarization conditions, accelerating the disintegration and delamination of the LSM electrode. The results indicate the potential detrimental effect of volatile boron on the electrochemical activity and stability of LSM oxygen electrodes of solid oxide electrolyzers.
... Despite its main drawback -requirement for low volatility of used materials as well as high viscosity, there are reports of screen-printing method being employed in fabrication of solar cells (Krebs et al., 2007;Mohammadi et al., 2012). Most common way to utilize screen-printing when handling perovskites is fabrication of thick film gas sensors (Cerdà et al., 2002;Martinelli et al., 1999) and cathodes for fuel cells (Herle et al., 2001;Bebelis et al., 2006). ...
Recent advancements in the area of perovskite photovoltaics have drawn wide attention of scientific community, mainly because of exceptional light absorbing properties exhibited by these organometallic halides. One of the main advantages perovskites have is their ability to be processed from solutions at relatively low temperatures. This paper briefly describes main structural, optical and electrical properties of perovskite materials, as well as the most popular solution processing techniques. We reflect on current progress in fabrication of solar cells containing organic-inorganic perovskites, device inner workings and effect of cell architecture on efficiency, along with prospective fine tuning of device properties through alteration of organometallic halide structure. Over the span of only three years, reported photoconversion efficiencies of such devices went from 3.8% to over 19%, with further increase being expected in near future. Finally, we describe other prospective applications for different perovskite materials. There is no doubt that perovskite photovoltaics possess great potential to provide bright future for the field of solar cells research, but whether they are going to live up to their expectations, remains to be seen.
... One is the vapor-phase deposition, such as physical vapor deposition (PVD) [8] or chemical vapor deposition (CVD) [9] and spray pyrolysis in its three versions: electrostatic (using a high voltage) [10,11], pressurized gas (using a stream of gas at high velocity) [3,12] and ultrasonic (using an ultrasonic irradiation) [13,14]. Another is the liquid-phase deposition, such as the sol-gel [15] and the particle deposition/consolidation method, such as tape casting and screen printing methods [16]. Among them, the spray pyrolysis techniques are very attractive for the industry of planar SOFCs, because they allow the deposition of a wide variety of ceramic films over large areas. ...
The development of solid oxide fuel cell has shown that the thin film concept for the electrode supported designs, based on the yttria-stabilized zirconia, is more promising than the research of new electrolyte materials. In this work, the spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on porous ceramic substrates. High porosity LSM, a typical material of SOFC cathodes, was used as substrate. The precursor solution was obtained by zirconium and yttrium salts dissolved in a mixture of ethanol and propylene glycol, with volume ratio 1:1. The substrate was heated and maintained at a constant temperature (280°C, 340°C or 560°C). The as-obtained films were heat treated in a temperature of 700°C, aiming to obtain yttria-stabilized-zirconia films from the amorphous film. The morphology and microstructure of the films were characterized by scanning electron microscopy and X-ray diffraction.
... The development of new materials with a superior ionic conductivity compared to yttriastabilized zirconia has also been attracted the interest to be used as SOFC electrolyte, as gadolinea or samaria-doped ceria which have higher ionic conductivity in lower temperatures than YSZ. Many processes have been employed to produce electrolyte films for intermediate temperature solid oxide fuel cell, for example: physical vapor deposition (PVD) [7], chemical vapor deposition (CVD) [8], screen-printing [9], sol-gel [10] and spray pyrolysis [11]. Compared to the other techniques mentioned, spray pyrolysis process uses simple and cheap equipment. ...
The development of solid oxide fuel cell with thin film concepts for an electrode supported design based on the yttria-stabilized zirconia has demonstrated favourable results due to its high chemistry stability in oxidization and environment reduction. The spray pyrolysis process was investigated in order to obtain dense thin films of YSZ on different substrates. The precursor solution was obtained by zirconium and yttrium salt dissolutions in a mixture of water and glycerine in several ratios to study the solvent influence. The substrate was initially heated at 600 °C and during the deposition it ranged from 260-350°C, finishing at a fast increase in temperature of 600°C. The heat treatment was carried out in four different temperatures: 700 °C, 750 °C, 800 °C, and 900 °. The precursors were characterized by thermal analysis. The microstructures of the films were studied using scanning electron microscopy and X-ray diffraction. The results obtained showed that the films obtained were crystalline before the heat treatment process and have shown ionic conductivity above 800°C.
... Various deposition methods have been used in the fabrication of electrolytes for intermediate temperature SOFC or thermal barrier coatings (TBC) such as electrochemical vapor deposition (EVD) [1], physical vapor deposition (PVD) [2], vacuum plasma spraying [3], tape calendaring [4], screen-printing [5] and spray pyrolisis [6]. However, these technologies require costly investment and complicated operation and do not allow a control of the coatings microstructure. ...
The objective of this research is to develop a novel process for SOFC electrolytes and fully ceramic TBC to prepare yttria stabilized zirconia (YSZ) by both a sol-gel derived route and a dip-coating method. The research focuses on the development of a process compatible with industrial requirements in terms of cost and easiness to processing. The microstructure of dip-coated thick films is studied by varying the characteristics of an organic YSZ suspension (concentration, rheology) used as coating bath. The suspension was obtained by addition of a polymeric matrix in a stable suspension of YSZ powders dispersed in an azeotropic MEK-EtOH mixture. The obtained films are continuous, homogeneous and films thicknesses vary between 1 to 100 μm. Different microstructures are obtained depending on the synthesis parameters of the slurry composition. The microstructure of the films is found to depend on the YSZ precursor powders content and the polymeric sol /dispersant solution (EtOH-MEK) ratio. Finally, the dip-coated suspensions are used to prepare dense or porous layers according to the applications. The coating microstructure is engineered to decrease sintering ability, to be gas-tight for fuel cells electrolytes or to enhance thermal shock resistance for Thermal Barrier applications.
... Neste caso, o anodo passa a ser o suporte da PaCOS-TI na superfície do qual o filme fino de eletrólito é depositado [1][2][3][4][8][9][10][11][12][13][14][15][16][17][18]. 19], deposição eletroquímica a vapor [12], moldagem em fitas [13][14][15], aerografia [1,[9][10][11]16], recobrimento sobre rotação [17,18] e serigrafia [20]. [21][22][23][24]. ...
To reduce the operating temperature of solid oxide fuel cells, structures with thin films electrolytes, deposited by spray coating on porous anode were developed. The slurries used for the fabrication of the films were prepared using appropriates suspensions with ytria-stabilized zirconia (YSZ) powers, solvents, dispersants, binders and plasticizers appropriates. In this work the study of the influence of the binders in the stability of the suspensions and the microstructures properties of the YSZ films were done. Three slurries were made with different composition of binders (0.5; 1.0 and 2.0 % in weight). All of them showed pseudo-plastics and thixotropics flow behavior, according to viscosities measurements and shear rate. The films were sintered to 1500 ºC /6 hours. The images of scanning electron micrographs (SEM) were treated by Quantikov program to determine the porosity of the film and average grain size of YSZ. The films showed adequate porosity for being used as SOFC electrolyte (between 0.2 and 0.4%) and average grain size between 2.0 and 6.0 µ m. The spray coating is a suitable technique to fabricate the YSZ electrolytes for SOFC.
... Actually, the cell was under a polarization condition when the AC-impedances were measured. It is expected that the reduction of the molecular oxygen to oxygen ions as well as the oxygen ion concentration around the reaction region can be greatly enhanced by the electric current [17,21,22]. Therefore, a decrease of oxygen diffusion resistance can be expected. ...
This study presents the electrochemical performance of (Ba0.5Sr0.5)0.9Sm0.1Co0.8Fe0.2O3−δ (BSSCF) as a cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). AC-impedance analyses were carried on an electrolyte supported BSSCF/Sm0.2Ce0.8O1.9 (SDC)/Ag half-cell and a Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF)/SDC/Ag half-cell. In contrast to the BSCF cathode half-cell, the total resistance of the BSSCF cathode half-cell was lower, e.g., at 550 °C; the values for the BSSCF and BSCF were 1.54 and 2.33 Ω cm2, respectively. The cell performance measurements were conducted on a Ni-SDC anode supported single cell using a SDC thin film as electrolyte, and BSSCF layer as cathode. The maximum power densities were 681 mW cm−2 at 600 °C and 820 mW cm−2 at 650 °C.
... Planar SOFC anode supports are usually fabricated by tape casting, a well-known technique easy to upscale[22,23]. The technique uses slurries dispersed by a wet ball-milling process with an optimized composition of solvent, dispersant, binder, plasticizer and defoamer. As this study is focused on the powder size, pore-former and the phase proportions of the samples, and not on the optimization of the wet slurry, a dry ball-milling process was used, with Turbula ® equipment followed by an isostatic compaction in cylinder shape. ...
The main drawback of Ni/YSZ anode supports for solid oxide fuel cell application is their low tolerance to reducing and oxidizing (RedOx) atmosphere changes, owing to the Ni/NiO volume variation. This work describes a structured approach based on design of experiments for optimizing the microstructure for RedOx stability enhancement. A full factorial hypercube design and the response surface methodology are applied with the variables and their variation range defined as: (1) NiO proportion (40–60wt% of the ceramic powders), (2) pore-former proportion (0–30wt% corresponding to 0–64vol.%), (3) NiO particle size (0.5–8μm) and (4) 8YSZ particle size (0.6–9μm).To obtain quadratic response models, 25 different compositions were prepared forming a central composite design. The measured responses are (i) shrinkage during firing, (ii) surface quality, (iii) as-sintered porosity, (iv) electrical conductivity after reduction and (v) expansion after re-oxidation. This approach quantifies the effect of all factors and their interactions. From the quadratic models, optimal compositions for high surface quality, electrical conductivity (>500Scm−1 at room temperature) and RedOx expansion (
... Similarly, the electrolyte is a fundamental component of the cell and care must be taken to produce a defect-free film. For this, most thin-film deposition techniques have been employed to produce YSZ electrolytes [46], for example colloidal dispersion casting [41], tape casting [47], dip coating [48], spray pyrolysis deposition of precursors [49,50], chemical vapor deposition [51], DC sputtering [52,53], RF sputtering [54], pulsed laser deposition [55], plasma spraying [56], etc. ...
One of the most promising technologies for future applications of solide oxide fuel cells (SOFC)is the so-called “anode-supported” configuration: a dense yttria-stabilised zirconia (YSZ) ceramic electrolyte is deposited as a thin film over a porous Ni / YSZ cermet substrate anode, followed by a porous ceramic cathode such as La1-xSrxMnO3 (LSM). In this paper, a short review is made of the current technologies available to achieve this particular architecture, and to optimise the service behaviour. Then, alternative materials and fabrication technologies, as well as their possible impact on performance, are proposed and investigated.
... Neste caso, o anodo passa a ser o suporte da PaCOS-TI na superfície do qual o filme fino de eletrólito é depositado [1][2][3][4][8][9][10][11][12][13][14][15][16][17][18]. 19], deposição eletroquímica a vapor [12], moldagem em fitas [13][14][15], aerografia [1,[9][10][11]16], recobrimento sobre rotação [17,18] e serigrafia [20]. [21][22][23][24]. ...
Para reduzir a temperatura de operação das pilhas a combustível de óxido sólido (PaCOS), estruturas com filmes finos de eletrólito depositados, por aerografia, sobre suportes de anodo porosos foram desenvolvidas. As barbotinas, empregadas para fabricação dos filmes, foram preparadas a partir de suspensões com pós de zircônia estabilizada com ítria (ZEI), solventes, dispersantes, ligantes e plastificantes apropriados. Neste trabalho, foi feito o estudo da influência dos ligantes sobre a estabilidade das suspensões e as propriedades microestruturais dos filmes de ZEI. Três barbotinas foram elaboradas com composições diferentes de ligantes (0,5; 1,0 e 2,0 % p/p). Todas apresentaram comportamento de fluidos pseudoplásticos e tixotrópicos, de acordo com medidas de viscosidade e taxa de cisalhamento. Os filmes foram sinterizados a 1500 ºC/6h. As micrografias eletrônicas de varredura (MEV) foram tratadas através do programa Quantikov para determinar a porosidade do filme e o tamanho médio de grão da ZEI. Os filmes apresentaram porosidade adequada para serem empregados como eletrólito das PaCOS (entre 0,2 e 0,4 % ) e tamanho médio de grão entre 2,0 e 6,0 µm. A técnica de aerografia é adequada para fabricar eletrólito de ZEI para PaCOS.
... It is why many recent investigations deal with the reduction of the electrolyte thickness of 5-10 m [1][2][3][4][5]. The most useful and lowest cost routes for preparing a dense layer of YSZ are based on wet chemical coating processes, such as screen printing [6,7], vacuum slip casting and slip casting [8][9][10], tape casting [11][12][13], wet powder spraying [14][15][16] and sol-gel processes [17]. To obtain a very thin layer, the key point in all these processes is to use a submicron starting powder, taking care that powder particles are fully dispersed in the suspension. ...
This work is focused on the synthesis of nano-crystallised yttria stabilised zirconia (YSZ) powders by the spray pyrolysis method, the aim of the study being a better understanding of the influence of the spray pyrolysis parameters on the morphology of the produced powders. Spray pyrolysed powder consists of polycrystalline particles, which are spherical. Each particle consists of nanometric primary grains. The morphology of these polycrystalline particles was characterised by scanning electron microscopy (SEM), helium pycnometry, thermogravimetric analysis (TGA) and mass spectroscopy (MS), and the results are compared. Thus, particle size, particle size distribution and particle porosity were determined and correlated to the process parameters. Finally, by dilatometric measurements, sintering curves of pellets prepared from different sets of powders were analysed in regard of their morphologies. Two main conclusions could be deduced from these studies. Firstly, the process parameters influence both internal porosity and particle size distribution of the synthesised powders. Secondly, the morphologies of the spray pyrolysed nano-powders lead to particularly high sintering activities.
... Up to now, significant developments have been made to make thin film electrolytes. There are a number of approaches for thin film fabrication, such as chemical vapor deposition (CVD) [3], DC magnetron sputtering [4], tape casting [5], sol–gel dip-drawing [6], spray coating [7,8], plaster casting [9] and so on. Each technique has its advantages and disadvan-tages. ...
Screen-printing technology was developed to fabricate gas-tight yttria-stabilized zirconia (YSZ) electrolyte films on porous NiO–YSZ anode substrates for use in solid oxide fuel cells (SOFCs). Several key process parameters such as the starting YSZ powder, printing ink composition, printing time and sintering temperature were studied and reported in detail. SEM results revealed that the selected process parameters exerted obvious influences on the microstructure of the screen-printed YSZ films. Open-circuit voltages (OCVs) were used to evaluate the usage feasibility of screen-printed YSZ films in SOFCs. Cell performance test results showed that the above-mentioned parameters had crucial effects on the OCVs and power density of the prepared cells. Based on appropriate parameters, an OCV value of 1.081V and a power density of 0.96Wcm−2 were obtained at 800°C using hydrogen as fuel and ambient air as oxidant.
... However, the local temperature of Cells-1 and -4 might still be higher than the furnace temperature when gas combustion occurs due to the gas leakage. Because of thermal activation, the increase of local temperature causes the reductions of both ohmic and electrode polarization resistances and thereby overestimated cell performance [21,22]. Fortunately, correction for the local temperature can be made by comparing the ohmic resistances of cells tested at different temperatures. ...
Nickel oxide (NiO)/yttria-stabilized zirconia (YSZ) anode substrates were fabricated at four compaction pressures, 70, 200, 500 and 1000MPa, the particle size distributions of NiO and YSZ were investigated with the powders treated at different compaction pressures, and the effects of compaction pressure on the performance of anodes with and without pore-formers were investigated by studying the effects of compaction pressure on the sintering shrinkage, compaction density, sintered density and electrical conductivity of anodes and the performance of cells. Experimental results demonstrated that the mismatch in the sintering shrinkages of YSZ films and the anodes compacted at 70 and 1000MPa caused gas leakage across the films and thus a higher local temperature than the furnace temperature. The single cell with the anode using pore-former and compacted at 500MPa exhibited the best output performance of 2.66Wcm−2 at 800°C.
... There are a number of approaches for fabrication of thin electrolyte films including chemical vapor deposition (CVD) [6,19], sol-gel [7], DC magnetron sputtering [8], tape casting [9], screen printing [10,11], centrifugal casting [12], spray coating [13][14][15][16][17][18] and so on. Compared to the methods mentioned above, spray coating is a handy and cost-effective technique to fabricate thin electrolyte films. ...
Spray coating technique was developed to fabricate dense yttria-stabilized zirconia (YSZ) electrolyte films onto NiO–YSZ porous anode substrates. A single fuel cell of Ni–YSZ/YSZ (14.9 μm)/LSM–YSZ was successfully prepared by spray coating technique. The cell was tested using humidified hydrogen as fuel and ambient air as oxidant. The cell provided the maximum power densities of 234, 721 and 990 mW/cm2 at 700, 750 and 800 °C, respectively. The impedance spectra showed that the performance of the cell was controlled by the electrode polarization rather than the resistance of YSZ electrolyte film. SEM results revealed that the YSZ film was crack-free, continuous and quite dense.
In this study, thin molybdenum‐containing, nickel‐based metal‐supported solid oxide fuel cells (MS‐SOFCs) were fabricated through atmospheric plasma spraying and then characterized. We investigated the change in cell performance associated with the reduction of the Ni–Mo support layer thickness from 200 to 80 µm and reduction of the substrate sintering temperature from 1200 to 1000°C. At a cell voltage of 0.6 V, the measured maximum power density values of a 50 × 50 mm ² MS‐SOFC were 313, 581, 890, and 1098 mW cm ⁻² at 600, 650, 700, and 750°C, respectively. A 100 × 100 mm ² (commercial‐size) MS‐SOFC and an assembled single‐cell MS‐SOFC stack exhibited electric output power values of approximately 33 and 39 W at 700 and 750°C, respectively, and an effective electrode area of 81 cm ² . In a long‐term stability test, the commercial‐size cell and single‐cell stack exhibited a degradation rate of approximately 1% after 1000 h of operation at a current density of 250–300 mA cm ⁻² and temperature of 700°C. Moreover, a five‐cell MS‐SOFC stack demonstrated a stack power of 180.85 W at 3.792 V (446.5 mW cm ⁻² at 0.758 V) and 750°C.
Exploring highly active cathode materials with fast cathodic oxygen reduction has been considered as one of the most promising approaches to accelerate the commercialization process of intermediate temperature solid oxide fuel cells (IT -SOFCs). Herein, a highly active hybrid catalyst system with multiphase heterointerfaces consisting of (PrSr)Ni0.5Mn0.5O3-δ, PrOx nanoparticles and (PrSr)2(MnNi)O4-δ is self-assembly formed by substitution of Sr into Pr2Ni0.5Mn0.5O4-δ (S-PNM). Further using S-PNM as cathode materials for IT-SOFCs, S-PNM achieves a remarkable maximum power density of 960 mW cm⁻² at 800 °C and an outstanding short-term stability with the discharge voltage of 0.68 V for 80 h. The excellent electrochemical performance by the preliminary experimental results is attributed to the coexistence of multiphase heterointerfaces of (PrSr)Ni0.5Mn0.5O3-δ, (PrSr)2(MnNi)O4-δ and PrOx nanoparticles, which can accelerate cathodic oxygen reduction.
The metal‐supported solid oxide fuel cell (MS‐SOFC) consisting of a porous Ni‐Mo as metal‐support, a La0.75Sr0.25Cr0.5Mn0.5O3–δ (LSCM) as diffusion barrier layer, a nano‐structured Ce0.55La0.45O3–δ (LDC)‐Ni as anode layer, a LDC as anode interlayer, a La0.8Sr0.2Ga0.8Mg0.2O3–δ (LSGM) as electrolyte, a Sm0.15Ce0.85O3–δ (SDC) as cathode interlayer, a 50 wt.% SDC–50 wt.% Sm0.5Sr0.5CoO3–δ (SSC) as composite cathode interlayer and a 25 wt.% SDC–75 wt.% SSC as cathode current collector are prepared by atmospheric plasma spraying (APS). The 25 cm² cell delivers maximum power densities of 962 and 1,119 mW cm⁻² at 700 and 750 °C. The durability, thermal cycling and redox cycling tests of this cell show the cell have good durability, thermal cycle stability and redox stability. The assembled single cell stack of 100 cm² cell shows electric output powers of 39 W (481 mW cm⁻²) and 27.4 W (338 mW cm⁻²) at 750 °C and 700 °C. The long‐term stability test of this single cell stack shows a degradation rate of about 0.77% k⁻¹ h⁻¹ over 1,770 h at 400 mA cm⁻² and 700 °C. Furthermore, a 25‐cell MS‐SOFC stack is assembled to evaluate the power performance and it shows a stack power of 829.8 W at 19.85 V and 740 °C.
Layered perovskite oxides are well known to possess significant electronic, magnetic and electrochemical properties. Herein, we highlight a novel layered perovskite PrBaMn1.5Fe0.5O5+δ (PBMFO) as electrodes of symmetrical solid oxide fuel cells (SSOFCs). The layered PBMFO shows high electrical conductivity of 112.5 and 7.4 S cm⁻¹ at 800 °C in air and 5% H2/Ar, respectively. The single cell with PBMFO symmetric electrodes achieves peak power density of 0.54 W cm⁻² at 800 °C using humidified hydrogen as fuel. Moreover, PBMFO electrodes demonstrate good redox stability and high coking tolerance against hydrocarbon fuel.
Most technologies for fabricating solid oxide fuel cells (SOFCs) are adopted from ceramic-fabrication methods. Selecting an appropriate method of preparing SOFC components is a main concern for many researchers because the method can strongly affect SOFC properties and performance. The method must be reproducible and highly controllable to improve SOFC performance and durability. SOFC fabrication methods have been customized to achieve high power outputs at low operation temperatures and thus broaden the choice of material and reduce fabrication cost. This article provides an overview of planar SOFC fabrication methods. Planar SOFC fabrication methods such as uniaxial pressing, tape casting, screen printing, dip coating, and slurry spin coating are discussed because these methods are cost effective. This article also discusses the technical parameters that can influence the processes of these methods and SOFC performance. The methods of preparing the materials of SOFC components are discussed because these methods directly affect the fabrication process.
The developed metal-supported solid oxide fuel cell consisting of a Ni-MoFe metal substrate as cell support, a double layer formed of La0.75Sr0.25Cr0.5Mn0.5O3-δ (LSCM) and nanostructured Ce0.55La0.45O2.δ -Ni (LDC-Ni) as anode, an LDC as anode interlayer, an La0.8Sr0.2Ga0.8Mg0.2O3-δ (LSGM) as electrolyte, a Sm0.15Ce0.85O3-δ (SDC) as barrier layer and a Sm0.5Sr0.5CoO3.-δ (SSC) as cathode is prepared using an atmospheric plasma spraying (APS) coating process. The measured maximum output power densities are 788, 666, 497 and 317 mW cm-2 at 750, 700, 650 and 600 °C respectively. In the 280 h durability test at 400 mA cm-2 constant current density and 650 °C, the measured voltages starting from 822 mV and ending at 775 mV show a degradation rate of about 20% kh-1, but after the tested cell is heat treated at the 800 °C and OCV condition for 4 h, the measured voltage at 400 mA cm-2 constant current density load and 650 °C is back to 825 mV that is greater than the initial cell voltage of 822 mV. All of the I-V curves, I-P curves, AC impedances and the voltages measured before and after the durability test show that the tested cell is recovered and demonstrate that the heat treated process around 8I0°C and at OCV condition for 4 h is effective to recover the performance of the prepared metal supported cell. The phenomenon of the recoverable cell performance is also observed in the experimental data of another prepared metal supported cell heated in the same furnace.
The BaZr0.63Ce0.27 Y0.10O2.95/ZnO/NaCl (BZCY-Z2-Cl) proton conductors with the heterogeneous structure were synthesized with NaCl of 5%, 10% and 15% (in mole fraction) to ZnO of 2% doped BaZr0.63Ce0.27Y0.10O2.95 proton conductors (i.e., BZCY-Z2) through a mechanical-mixing process and sintering at 1 400 °C for 4 h. The results show that the sintering temperature and soaking time can be reduced due to the presence of liquid phase after the addition of NaCl added as a sintering aid. Therefore, the sintering properties of the BZCY-Z2-Cl proton conductor are improved by the addition of NaCl. NaCl is homogeneously distributed on the grain boundary, changing the characteristics of grain boundary. As a result, the protonic conduction along the grain boundary is enhanced. The total conductivity of the protonic conductor reaches 7.48 × 10-3 S/cm at 700 °C in wet hydrogen. The experimental results of a single fuel cell with electrolyte-supported configuration reveal that the ionic transport number is 0.97, 0.97, 0.95 and 0.93 at 550, 600, 650 and 700 °C, respectively, revealing that it is a superior protonic conductor. It also deliveries a maximum output power density of 17 mW/cm2 at 700 °C. The lower output power density is due to a thick electrolyte (0.9 mm in thickness). These indicate that the superior electrochemical performance of the NaCl-modified protonic conductor could be obtained.
Decalcomania is a new method for SOFCs (solid oxide fuel cells) unit cell fabrication. A tight and dense 5μm Yttria-stabilized zirconia (8YSZ) electrolyte layer on anode substrate was fabricated by the decalcomania method. After 8YSZ as the electrolyte starting material was calcined at 1200° the particle size was controlled by the attrition mill. The median particle size (D50) of each 8YSZ was 39.6μm, 9.30μm, 6.35μm, and 3.16μm, respectively. The anode substrate was coated with decalcomania papers which were made by using 8YSZ with different median particle sizes. In order to investigate the effect of median particle sizes and sintering conditions on the electrolyte density, each sample was sintered for 2, 5 and 10 h, respectively. 8YSZ with a median particle size of 3.16μm which was sintered at 1400°C for 10 had the highest density. With this 8YSZ, a SOFCs unit cell was manufactured with a 5μm layer by the decalcomania method. Then the unit cell was run at 800°C. The Open Circuit Voltage (OCV) and Maximum power density (MPD) was 1.12 V and 650 mW/cm 2, respectively.
Solid Oxide Fuel Cell (SOFC) is a solid-state electrochemical device that converts the chemical energy of a fuel directly into electrical energy. Due to its multi-fold inherent advantages SOFC is projected as the power source for the future generation. All over the world, extensive research activities are being pursued for the past decade and accordingly an immense wealth of literature is avaitable in this field of research. Though this field of research activity is very wide and multidisciplinary, this review is mainly directed towards the processing, properties and fabrication of the state of the art ceramic materials, viz., yttria stabilized zirconia (YSZ) as the electrolyte material, Sr-doped LaMnO3 as the cathode material, Ni-YSZ cermet as the anode material and Ca-doped LaCrO3 as the interconnect material, that are being considered for the development of present day SOFC power modules. Special attention is given to the development of planar SOFC components fabrication taking into consideration the advantages of the planar design compared to the tubular design. A brief account of the future research and development direction is also discussed with an emphasis to widen the scope of materials research in the area of solid oxide fuel cells.
Many studies have been reported in the literature related to YSZ films deposited on dense substrate or applied directly on the SOFC anode. However, there are not a lot of studies about the YSZ deposition on the cathode. The present work aims to obtain yttria-stabilized zirconia (YSZ), using the spray pyrolysis technique, for their application as electrolyte in solid oxide fuel cells (SOFC). The films were obtained from a precursor solution containing zirconium and yttrium salts, dissolved in ethanol and propylene glycol (1:1), this solution was sprayed onto a heated LSM porous substrate. The substrate temperature was varied in order to obtain dense and homogeneous films. After deposition, the films were heat treated, aiming to crystallize and stabilize the zirconia cubic phase. The films were characterized by Scanning Electron Microscopy (SEM), thermal analysis, X-ray diffraction and Fourier transform Infrared Spectroscopy (FT-IR).
Recent research results show that homogeneity and microstructure are very important parameters for the development of low cost materials with better performance for fuel cell applications. This research effort has been contributed in the development of low temperature solid oxide fuel cell (LTSOFC) material and technology as well as applications for polygeneration. The microstructure and electrochemical analyses were conducted. We found a series of new electrode materials which can run solid oxide fuel cell at 300-600°C range with high performances, e.g., a high power density output of 980 mW cm-2 was obtained at 570°C. The fuel cell electrodes were prepared from metal oxide materials through a solid state reaction and then mixed with doped ceria. The obtained results have many advantages for the development of LTSOFCs for polygeneration. The nanostructure of the anode has been studied by high-resolution electron microscopy, the crystal structure and lattice parameters have also been studied by X-ray diffraction. The electrical conductivity of the composite anode was studied by electrochemical impedance spectra.
(La0.8Sr0.2)0.95MnO3 (LSM95) cathode supported Zr0.89Sc0.1Ce0.01O2�x (SSZ) electrolytes with
LSM-SSZ active cathode layers were fabricated using the tape-casting, lamination and cosintering
techniques. The loadings of pore-formers in the cathode support layers and the
active cathode layers were optimized through impedance measurement on symmetrical
cathode fuel cells. The pore size distribution and porosity of cathode-support substrates
were measured using the mercury intrusion porosimetry. The open circuit voltage and
maximum power density of cathode-support solid oxide fuel cells with NiO/SSZ cermet
anodes were 1.10 V and 0.325 W cm�2 at 750 �C with H2 as fuels and air as oxidants.
The major challenge for the commercialization of SOFCs is to reduce high manufacturing costs. By simplifying the sintering process and reducing the sintering temperature in the fabrication process, the manufacturing costs of SOFC could be lowered significantly. A low-temperature co-firing process for three layers of SOFC including cathode (LSM/YSZ, [LSM:(La,Sr) MnO3),YSZ:Y2O3-ZrO2]), electrolyte(YSZ) and anode (YSZ/NiO) has been developed. The anode substrate of NiO/YSZ was formed and pre-sintered at 1000 ° for 2 hours, then the YSZ electrolyte layer and LSM/YSZ cathode layer were deposited successively, and finally the anode-supported SOFCs were fabricated by co-firing at 1200 ° for 5 hours. In order to minimize the mismatch in sintering shrinkage among the components of the cell, various amounts of pore former were added to the anode and cathode layers. The mismatch in sintering shrinkage is minimized by adding 15wt% of pore former to the anode and 20wt% to the cathode. The OCV of the co-fired anode-support trilayer cell was 1.05V at 800 °. The power density of this cell was 0.47W/cm2 at 800°.
A gas-tight yttria-stabilized zirconia (YSZ) electrolyte film was fabricated on porous NiO–YSZ anode substrates by a binder-assisted slurry casting technique. The scanning electron microscope (SEM) results showed that the YSZ film was relatively dense with a thickness of 10 μm. La0.8Sr0.2MnO3 (LSM)–YSZ was applied to cathode using a screen-print technique and the single fuel cells were tested in a temperature range from 600 to 800 °C. An open circuit voltage (OCV) of over 1.0 V was observed. The maximum power densities at 600, 700, and 800 °C were 0.13, 0.44, and 1.1 W cm–2, respectively.
The properties of SOFC unit cells manufactured using the decalcomania method were investigated. SOFC unit cell manufacturing using the decalcomania method is a very simple process. In order to minimize the ohmic loss of flattened tube type anode supports of solid oxide fuel cells(SOFC), the cells were fabricated by producing an anode function layer, YSZ electrolyte, LSM electrode, etc., on the supports and laminating them. The influence of these materials on the power output characteristics was studied when laminating the components and laminating the anode function layer between the anode and the electrolyte to improve the output characteristics. Regarding the performance of the SOFC unit cell, the output was 246 at a temperature of in the case of not laminating the anode function layer; however, this value was improved by a factor of two to 574 due to the decrease of the ohmic resistance and polarization resistance of the cell in the case of laminating the anode function layer. The outputs appeared to be as high as 574 and 246 at a temperature of in the case of using decalcomania paper when laminating the electrolyte layer using the in dip-coating method; however, the reason for this is that interfacial adhesion was improved due to the dense structure, which leads to a thin thickness of the electrolyte layer.
Development of high performance cathodes with low polarization resistance is critical to the success of solid oxide fuel cell (SOFC) development and commercialization. In this paper, (La0.8Sr0.2)0.9MnO3 (LSM)–Gd0.2Ce0.8O1.9(GDC) composite powder (LSM ~70 wt%, GDC ~30 wt%) was prepared through modification of LSM powder by Gd0.2Ce0.8(NO3)x
solution impregnation, followed by calcination. The electrode polarization resistance of the LSM–GDC cathode prepared from the composite powder was ~0.60 Ω cm2 at 750 °C, which is ~13 times lower than that of pure LSM cathode (~8.19 Ω cm2 at 750 °C) on YSZ electrolyte substrates. The electrode polarization resistance of the LSM–GDC composite cathode at 700 °C under 500 mA/cm2 was ~0.42 Ω cm2, which is close to that of pure LSM cathode at 850 °C. Gd0.2Ce0.8(NO3)x
solution impregnation modification not only inhibits the growth of LSM grains during sintering but also increases the triple-phase-boundary (TPB) area through introducing ionic conducting phase (Gd,Ce)O2-δ, leading to the significant reduction of electrode polarization resistance of LSM cathode.
In this study, the physical properties of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics were measured and their potential for use as a cathode material of intermediate-temperature solid oxide fuel cells (IT-SOFCs) was evaluated. A cubic phase was retained in all of the Sr1−xPrxCo0.95Sn0.05O3−δ ceramics. Analysis of the temperature-dependent conductivity found the SrCo0.95Sn0.05O3−δ and Sr0.9Pr0.1Co0.95Sn0.05O3−δ ceramics exhibiting semiconductor-like behavior below 550 °C and metal-like behavior above the same temperature. The Sr0.8Pr0.2Co0.95Sn0.05O3−δ and Sr0.7Pr0.3Co0.95Sn0.05O3−δ ceramics, however, reported a metal-like conductivity in the whole temperature range. The electrical conductivities of the Sr0.8Pr0.2Co0.95Sn0.05O3−δ ceramic at 500 °C and 700 °C read respectively 1250 S/cm and 680 S/cm, both of which were superior than those in most of the common perovskites. Single cells with a structure of NiO–Sm0.2Ce0.8O2−δ (SDC)/SDC/Sr0.8Pr0.2Co0.95Sn0.05O3−δ-SDC were built and characterized. Addition of SDC in Sr0.8Pr0.2Co0.95Sn0.05O3−δ emerged to be a crucial factor reducing the ohmic resistance (R0) and polarization resistance (RP) of the cell by facilitating a better adhesion to and electrical contact with the electrolyte layer. The R0 and RP of the cell read respectively 0.068 Ω cm2 and 0.0571 Ω cm2 at 700 °C and 0.298 Ω cm2 and 1.310 Ω cm2 at 550 °C. With no microstructure optimization and hermetic sealing of the cells, maximum power density (MPD) and open circuit voltage (OCV) reached respectively 0.872 W/cm2 and 0.77 V at 700 °C and 0.482 W/cm2 and 0.86 V at 550 °C. It is evident that Sr1−xPrxCo0.95Sn0.05O3−δ is a promising cathode material for IT-SOFCs.
In this study, SrCo1−ySbyO3−δ powders were prepared by a modified Pechini method. According to the study results, the cubic Pm3m phase of the SrCo1−ySbyO3−δ ceramics was obtained as 10% of cobalt ions were substituted by antimony ions. Doping of Sb3+ ions appeared both to stabilize the Pm3m phase of the SrCo1−ySbyO3−δ ceramics and to enhance densification and retard grain growth. The coefficient of thermal expansion of the SrCo1−xSbxO3−δ ceramics increased with the content of the antimony ions, ranging from 10.17 to 15.37 ppm/°C at temperatures lower than the inflection point (ranging from 450 °C to 550 °C) and from 22.16 to 29.29 ppm/°C at higher temperatures. For the SrCo0.98Sb0.02O3−δ ceramic, electrical conductivity reached a maximum of 507 S/cm at 450 °C. The ohmic and polarization resistances of the single cell with the pure SrCo0.98Sb0.02O3−δ cathode at 700 °C read respectively 0.298 Ω cm2 and 0.560 Ω cm2. The single cell with the SrCo0.98Sb0.02O3−δ-SDC composite cathode appeared to reduce the impedances with the R0 and RP at 700 °C reading respectively 0.109 Ω cm2 and 0.127 Ω cm2. Without microstructure optimization and measured at 700 °C, the single cells with the pure SrCo0.98Sb0.02O3−δ cathode and the SrCo0.98Sb0.02O3−δ-SDC composite cathode, demonstrated maximum power densities of 0.100 W/cm2 and 0.487 W/cm2. Apparently, SrCo1−ySbyO3−δ is a potential cathode for use in IT-SOFCs.
Composite cathodes based on La0.6Sr0.4Co0.2Fe0.8O3−δ (LSCF) are investigated for lower operating temperature (<750 °C) applications of a solid oxide fuel cell (SOFC). To enhance a charge transfer, a bi-layer SOFC cathode is proposed, which has a LSCF–Ce0.9Gd0.1O1.95 (GDC) composite layer and a pure LSCF layer. The bi-layer cathode SOFC shows a current density of 0.65 A cm−2 at 0.8 V and 660 °C, which is higher than a LSCF–GDC composite single-layer cathode SOFC cell of 0.35 A cm−2. The charge transfer polarizations in the bi-layer cathode SOFC are 0.14 Ω cm2 and 0.35 Ω cm2 at 760 °C and 660 °C, respectively, which are lower than those in the single-layer cathode cell of 0.23 Ω cm2 and 0.66 Ω cm2. The impedances characterized with a fitting model show that the lowered charge transfer polarization in the bi-layer cathode is a dominant factor in reducing the total polarization of SOFC.
In this study, introduction of tin ions in the SrCoO3 − δ oxide is attempted to modify its electrochemical behavior for serving as a cathode of intermediate-temperature solid oxide fuel cells (IT-SOFCs). Doping of tin ions appears to stabilize the cubic Pm-3m phase of the SrCo1 − ySnyO3 − δ ceramics but generates SrSnO3 precipitates and inhibits the grain growth as y value rises to a level greater than 10%. Obtained at 550 °C, the maximum electrical conductivity of SrCo0.95Sn0.05O3 − δ reads 545 S cm− 1. Single cells with a structure of NiO–Sm0.2Ce0.8O2 − δ (SDC)/SDC/SrCo0.95Sn0.05O3 − δ–SDC are built and characterized. Though SrCo0.95Sn0.05O3 − δ is regarded as an MIEC (mixed ionic/electronic conductivity material), adding SDC to SrCo0.95Sn0.05O3 − δ guarantees good adhesion to and fine electrical contact with the electrolyte layer, thereby contributing to the reduction in R0 and RP values. The single cell with the SrCo0.95Sn0.05O3 − δ–SDC composite cathode at 700 °C registers respectively an R0 value of 0.044 Ω cm2 and an RP value of 0.109 Ω cm2. In the absence of microstructure optimization and hermetic sealing of cells, a high power density of 0.847 W cm− 2 is reached. SrCo1 − ySnyO3 − δ thus emerges to be a promising cathode material for IT-SOFCs applications.
In order to identify new cathode compositions for the high temperature solid oxide fuel cell, we have investigated the effect of the trivalent cations Al and Ga at the Mn site of the well-studied cathode composition La0.84Sr0.16MnO3. All the compositions have been prepared by the low temperature citrate–nitrate auto-ignition process and sintered within the temperature range of 1150–1350 °C for 4 h. In order to understand the compatibility of the prepared samples as alternative cathode materials, we compared their electrical conductivity and thermal expansion coefficient with those of La0.84Sr0.16MnO3 and yttria-stabilized zirconia. A 10 mol% Al doped La0.84Sr0.16MnO3 composition exhibited a conductivity of around 122 S cm−1 at 950 °C and a thermal expansion coefficient of 11.04 × 10−6 K with a minimum reactivity towards yttria-stabilized zirconia. Though the conductivity of the new composition is lower than that of La0.84Sr0.16MnO3 (169 S cm−1 at 950 °C), it is still high enough for use as a cathode material.
SOFCs have the potential to meet the critical energy needs of our modern civilization and minimize the adverse environmental impacts from excessive energy consumption. They are highly efficient, clean and can run on a variety of fuel gases. However, wide adoption of SOFCs is currently hindered by cell durability, manufacturing cost, and lack of fundamental understanding on electrochemical performance of the cell. In order to evaluate the durability of SOFCs, a mathematical thermo-mechanical model was developed to provide the distribution of thermal stresses during thermal cycling, and predict the lifetime of a cell. In addition, an ultrasonic spray pyrolysis prototype fabrication setup, which has the ability to tailor the microstructure of the deposited film, was established as an economically practical fabrication method to deposit the electrode of SOFC. Then, the electrochemical performances of deposited cells with tailored microstructures were investigated in order to better understand the impact of fabrication process parameters on cell electrochemical performance using AC electrochemical impedance spectroscopy. Furthermore, a complete electrode polarization model of SOFCs has been developed and utilized to analyze the performance of homogenous and functionally graded anode with different particle size and porosity profiles. The thermo-mechanical model study showed thermal stresses were more concentrated near the free edge. As the porosity and the thickness of anode increased, the lifetime of the cell decreased. The precursor solution concentration and deposition temperature were found to be the most critical parameters that influenced the microstructure. By manipulating deposited microstructures, the Area Specific Resistance (ASR) of the deposited anode improved and the activation energy decreased. The developed thermo-mechanical model is one of the first attempts to understand cyclic failure behavior of multilayer SOFC through theoretical approach. Low polarization and activation energy makes the developed prototype fabrication setup a promising candidate for the fabrication of high performance SOFC electrode with tailored microstructure. The study of developing electrode polarization model experimentally and numerically demonstrated the potential of controlling the electrode microstructure of a SOFC to improve the cell's electrochemical performance. The work contributes to the understanding of cell performance in relation to graded microstructures.
By using the atmospheric plasma spraying (APS) technique for SOFC fabrication, we can avoid the thermal failure between the components of SOFC which made from the traditional sintering method at high temperature. The advantage of porous metal supported SOFC produced by the APS process is that the process is simple and low cost. The purpose of this study was to manufacture a porous Ni/CeO2 anode of intermediate temperature SOFC. By introducing the pore former into the feedstocks, the porous structure of the Ni/CeO2 anode was obtained by plasma spraying method. In this study, the feedstock of the NiO/CeO2/Na2CO3 powder made by the spray granulation is spherical; the powder structure is compact and a hollow hole inside the powder, hence more porosity (29.1%) of the as-sprayed coating was found and the pore distribution is more uniform. The remainder oxygen vacancies are existed in the reduced anode coating. Use of undoped ceria as an anode material appears to be feasible. The NiO/CeO2/Na2CO3 powder formed the higher bonding strength coating with 33.6MPa. The electron conductivity was obtained with around 200S/cm in 700°C. The other properties of the anode were discussed in the paper.
Optimization of the electrode microstructure in a solid oxide fuel cell (SOFC) is an important approach to performance enhancement. In this study, the relationship between the microstructure and electrochemical performance of an anode electrode fabricated by ultrasonic spray pyrolysis was investigated. Nickel–Ce0.9Gd0.1O1.95 (Ni–CGO) anodes were deposited on a dense yttria stabilized zirconia (YSZ) substrate by ultrasonic spray pyrolysis, and the resulting microstructure was analyzed. Scanning electron microscope (SEM) examinations revealed the impact of deposition temperature and precursor solution concentration on anode morphology, particle size and porosity. The electrochemical performance of the anode was measured by electrochemical impedance spectroscopy (EIS) using a Ni–CGO/YSZ/Ni–CGO symmetrical cell. The deposited anode had a particle size and porosity in ranging between 1.5–17μm and 21%–52%, respectively. The estimated volume-specific triple phase boundary (TPB) length increased from 1.37×10−3μmμm−3 to 1.77×10−1μmμm−3as a result of decrease of the particle size and increase of the porosity. The corresponding area specific charge transfer resistance decreased from 5.45ohmcm2 to 0.61ohmcm2 and the activation energy decreased from 1.06eV to 0.86eV as the TPB length increased.
The LSGM(La0.8Sr0.2Ga0.8Mg0.2O3) electrolyte based intermediate temperature solid oxide fuel cells (ITSOFCs) supported by porous nickel substrates with different permeabilities are prepared by plasma spray technology for performance studies. The cell having a porous nickel substrate with a permeability of 3.4 Darcy, an LSCM(La0.75Sr0.25Cr0.5Mn0.5O3) interlayer on the nickel substrate, a nano-structured LDC(Ce0.55La0.45O2)/Ni anode functional layer, an LDC interlayer, an LSGM/LSCF(La0.58Sr0.4Co0.2Fe0.8O3) cathode interlayer and an LSCF cathode current collector layer shows remarkable electric output power densities such as 1270mWcm−2 (800°C), 978mWcm−2 (750°C) and 702mWcm−2 (700°C) at 0.6V cell voltage under 335mlmin−1 H2 and 670mlmin−1 air flow rates. SEM, TEM, EDX, AC impedance, voltage and power data with related analyses are presented here to support this high performance. The durability test of the cell with the best power performance shows a degradation rate of about 3%kh−1 at the test conditions of 400mAcm−2 constant current density and 700°C. Results demonstrate the success of APS technology for fabricating high performance metal-supported and LSGM based ITSOFCs.
YSZ/Ni is the conventionally most used material for making the anode of a solid oxide fuel cell. Agglomerated nanostructured YSZ/NiO powders and plasma spray are applied to produce nanostructured YSZ/NiO coatings on porous support substrates. After reduction in an ambient atmosphere of 7% hydrogen and 93% argon at about 800 °C for 4hours, a novel SOFC anode with nanostructured characteristics such as nano YSZ particles, nano Ni particles, nano pores and nano pore channels is produced. This new YSZ/Ni anode provides larger triple phase boundaries for hydrogen oxidation reactions. X-ray diffraction patterns of these YSZ/NiO coatings after 1h of heat treatment at temperatures from 700 to 1100 °C are obtained and Scherrer analysis is conducted to study the effect of temperature on grain size. The results obtained from SEM, TEM, XRD and EDX measurements and analyses are presented in this investigation.
Porous NiO-Ce0.8Sm0.2O1.9 (NiO-SDC) ceramics with homogeneous pore distribution were prepared using polystyrene (PS) spheres as pore templates. NiO-SDC powders were synthesized by a glycine-nitrate method, ultrasonically mixed with PS spheres in ethanol, dried and then pressed into green pellets. The pellets were sintered to yield porous NiO-SDC ceramics. The effects of the sintering temperature on the microstructure and mechanical strength of the ceramics were investigated. NiO-SDC ceramics sintered at 1200 and 1350°C have interconnected pore structures and high compression strength. When single cells were fabricated using porous NiO-SDC ceramics as anode-supported layers, the peak power density of the cells at 600°C was 333 and 353 mW·cm−2 for ceramics sintered at 1200 and 1350°C, respectively. The results indicated that these porous ceramic materials are promising for anode substrates for solid oxide fuel cells.
A gas-tight yttria-stabilized zirconia (YSZ) electrolyte film was fabricated on porous NiO–YSZ anode substrates by a modified slurry coating, i.e., a pressure-assisted slurry-casting technique. The SEM results showed that the YSZ film was fully dense with a thickness of 26μm. Combined with a screen-printed La0.7Sr0.3MnO3 (LSM)–YSZ cathode, a single fuel cell was tested in a temperature range from 650 to 850∘C with humidified hydrogen as fuel and ambient air as oxidant. The open circuit voltage (OCV) of over 1.0V was observed, which suggested that the fuel leakage across YSZ film was negligible. The maximum power density at 650, 700, 750, 800 and 850∘C were 208, 513, 837, 1116 and 1234mW/cm2, respectively. The results of impedance measurements revealed that the activation energy for the total ohmic resistance of the cell and for the total electrode polarization was 66.1 and 101.7kJ/mol, respectively. The cell performance was essentially governed by the electrode polarization. A short-term stability testing of the cell for 5h showed that the fuel cell was quite stable in the testing procedure.
Dense and thin electrolyte films are desirable for solid oxide fuel cells (SOFCs) because of their low gas leakage and low ohmic resistances. This work aims at the preparation of thin dense Gd-doped ceria (CGO) electrolyte films using a cost-effective deposition method in ambient atmosphere–electrostatic spray deposition (ESD). The deposition parameters such as deposition temperature, concentration and flow rate of precursor solution were changed systematically to examine their effects on film morphology and hence electrochemical performance. While the film morphology was examined by a scanning electron microscope, the electrochemical performance was revealed by measuring open circuit voltages (OCVs) of NiO-CGO/CGO/Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF) cells in 500–700 °C with humidified hydrogen as fuel and air as oxidant. The results show that a CGO film of 25 μm thick obtained at a deposition temperature of 400 °C, a precursor solution flow rate of 6 ml h–1 and a precursor concentration of 0.3 M was dense with very few isolated pores and the OCV of the associated cell was 0.915 V at 500 °C. This implies that the CGO film has negligible gas leakage and ESD is a promising method for preparing thin dense electrolyte films for SOFCs.
La0.8 Sr0.2FeO3-δ is a new kind of cathode material for intermediate SOFC, but its electrochemical activity is relative poor for the lanthanum gallate based solid oxide fuel cell. In this paper, a novel composite cathode of La0.8Sr0.2FeO3-δ/La0.9Sr0.1 Ga0.8Mg0.2O3-δ was prepared on the LSGM electrolyte substrate by screen-printing method. The results of cathodic polarization measurements show that the overpotential decreases significantly when the composite cathode is used instead of the La0.8Sr0.2 FeO3-δ single layer cathode. The cathodic overpotential of the composite La0.8Sr0.2FeO3-δ/La0.9Sr0.1Ga0.8Mg0.2O3-δ cathode is 150 mV at the current density of 0.2 A·cm−2 at 800 °C, while the cathodic overpotential of the La0.8Sr0.2 FeO3-δ single layer cathode is higher than 260 mV at the same condition. The electrochemical impedance spectroscopy was employed to investigate the polarization resistance of the cathode. The polarization resistance of the composite cathode is 1.20 ω·cm2 in open circuit condition, while the value of the single La0.8 Sr0.2FeO3-δ cathode is 1.235 ω·cm2.
The neodymium-deficient nickelate Nd1.95NiO4+δ, mixed conducting K2NiF4-type oxide, was evaluated as cathode for solid oxide fuel cells. The electrochemical properties were investigated on planar Ni–YSZ anode-supported SOFC based on co-tape casted and co-fired HTceramix® cells. Using a layer of strontium doped lanthanum cobaltite as current collector, a current density of 1.31Acm−2 (at 0.70V) was obtained at 800°C using hydrogen fuel with small single cells, after optimizing the cathode sintering temperature. Impedance spectroscopy measurements were performed; the different resistive contributions and the values of the corresponding equivalent capacities are discussed.
Intermediate temperature solid oxide fuel cells (ITSOFCs) supported by a porous Ni-substrate and based on Sr and Mg doped lanthanum gallate (LSGM) electrolyte, lanthanum strontium cobalt ferrite (LSCF) cathode and nanostructured yttria stabilized zirconia–nickel (YSZ/Ni) cermet anode have been fabricated successfully by atmospheric plasma spraying (APS). From ac impedance analysis, the sprayed YSZ/Ni cermet anode with a novel nanostructure and advantageous triple phase boundaries after hydrogen reduction has a low resistance. It shows a good electrocatalytic activity for hydrogen oxidation reactions. The sprayed LSGM electrolyte with ∼60μm in thickness and ∼0.054Scm−1 conductivity at 800°C shows a good gas tightness and gives an open circuit voltage (OCV) larger than 1V. The sprayed LSCF cathode with ∼30μm in thickness and ∼30% porosity has a minimum resistance after being heated at 1000°C for 2h. This cathode keeps right phase structure and good porous network microstructure for conducting electrons and negative oxygen ions. The APS sprayed cell after being heated at 1000°C for 2h has a minimum inherent resistance and achieves output power densities of ∼440mWcm−2 at 800°C, ∼275mWcm−2 at 750°C and ∼170mWcm−2 at 700°C. Results from SEM, XRD, ac impedance analysis and I–V–P measurements are presented here.
The electrical properties of Mn-doped YSZ (yttria stabilized zirconia) were investigated. The polarization cell was employed to determine the electronic conductivity of Mn 4 mol% doped YSZ (8 mol% Y2O3). The observed conductivities were 2.6×10−4 S cm−1 in air (p-tyee) and 1×10−4Scm−1 at the oxygen pressure of 10−14 Pa (n-type). The hole conductivity was hig her than that of Mn-free YSZ by about one order of magnitude. The transference number of oxide ion was higher than 0.99 in the oxygen potential range from 10−15 to 105 Pa. The ionic conductivity showed oxygen-pressure dependence, which was explained by oxygen-vacancy formation due to the valence change of Mn ion in the YSZ lattice. The electrochemical impedance was studied with Pt electrode on Mn-doped surface of YSZ. It was suggested that the mixed valence state of the Mn ion affected the response of the electrode.
In order to clarify the extent of oxygen nonstoichiometry and defect equilibrium in the oxide solid solution La1-xSrxCoO3-δ (x = 0, 0.1, 0.2, 0.3, 0.5, and 0.7), thermogravimetric measurements were made in the range 10-5 ≤ P(O2) atm ≤ 1 and 300 ≤ T °C ≤ 1000, where the solid solution was stable as a single-phase perovskite-type oxide. The nonstoichiometry, δ, increases with decreasing P(O2), increasing Sr content, x, and increasing temperature, T. At temperatures below 800°C, δ of LaCoO3-δ could not be detected. For La0.3Sr0.7CoO3-δ, a large δ was observed at temperatures as low as 300°C. The observed δ for each La1-xSrxCoO3-δ ranges between 0 and values slightly in excess of x 2. Using the Gibbs-Helmholtz equation, the partial molar enthalpy and entropy of oxygen, (hO - hO°) and (sO - sO°) respectively, were calculated as a function of x and δ. The value of (hO - hO°) decreases linearly with increasing δ. The δ dependence of (sO - sO°) is determined by the configurational entropy of V··O and OxO on the oxygen sublattice, while no noticeable contribution was detected from the configurational entropy due to electronic states. This is consistent with the metallic character of the electronic conduction in La1-xSrxCoO3-δ.
The cathodic polarization of the electrodes sputtered on yttria stabilized zirconia electrolyte was studied at 800°C in air. The system showed high electrode activity for oxygen reduction. The study of the electrode resistance as functions of and temperature revealed that the rate‐determining steps for oxygen reduction were as follows: the charge transfer process for , the dissociation of oxygen molecules on the surface for and , and the oxygen diffusion on the electrode surface for . The marked electrode activity of was explained by the large effective reaction surface area, which is caused by the high oxide ion diffusivity and the high dissociation ability of oxygen molecules. In , the ability of the dissociation of oxygen molecules was considered to be lower than that in . The low activity of Cr‐perovskite electrode was explained by the low diffusivity of oxygen ions.
Solid oxide fuel cells produce electricity at very high efficiency and have very low to negligible emissions, making them an attractive option for power generation for electric utilities. However, conventional SOFC`s are operated at 1000{degrees}C or more in order to attain reasonable power density. The high operating temperature of SOFC`s leads to complex materials problems which have been difficult to solve in a cost-effective manner. Accordingly, there is much interest in reducing the operating temperature of SOFC`s while still maintaining the power densities achieved at high temperatures. There are several approaches to reduced temperature operation including alternative solid electrolytes having higher ionic conductivity than yttria stabilized zirconia, thin solid electrolyte membranes, and improved electrode materials. Given the proven reliability of zirconia-based electrolytes (YSZ) in long-term SOFC tests, the use of stabilized zirconia electrolytes in reduced temperature fuel cells is a logical choice. In order to avoid compromising power density at intermediate temperatures, the thickness of the YSZ electrolyte must be reduced from that in conventional cells (100 to 200 {mu}m) to approximately 4 to 10 {mu}m. There are a number of approaches for depositing thin ceramic films onto porous supports including chemical vapor deposition/electrochemical vapor deposition, sol-gel deposition, sputter deposition, etc. In this paper we describe an inexpensive approach involving the use of colloidal dispersions of polycrystalline electrolyte for depositing 4 to 10 {mu}m electrolyte films onto porous electrode supports in a single deposition step. This technique leads to highly dense, conductive, electrolyte films which exhibit near theoretical open circuit voltages in H{sub 2}/air fuel cells. These electrolyte films exhibit bulk ionic conductivity, and may see application in reduced temperature SOFC`s, gas separation membranes, and fast response sensors.
The amorphous citrate process has been used to produce Mn2O3, Mn3O4, LaMnO3, SrMnO3 and strontium-substituted LaMnO3. The citrate-nitrate gels were dehydrated at 70 C to yield solid precursor materials. The decomposition/oxidation of the precursors have been studied using thermogravimetry and evolved gas analysis. The products of decomposition have been characterized by X-ray diffraction analysis, scanning electron microscopy and, in the case of the strontium-substituted LaMnO3, by analytical electron microscopy. The surface area and residual carbon content of the strontium-substituted LaMnO3 have been determined as a function of the decomposition/oxidation temperature. Both the process yield and compositional homogeneity of the strontium-substituted LaMnO3 have been shown to increase as the decomposition temperature increases. The residual carbon content has been shown to decrease as decomposition temperature increases. However, the surface areas of the powders decrease significantly as decomposition temperature increases. Consequently, it is evident that there is a conflict in the experimental conditions required for optimum yield, homogeneity and residual carbon content compared to those required for maximum surface area.
Reduced temperature operation of SOFC at ECN
- Van Berkel
- F P F Christie
- G M Heuveln
- F H Huijsmans
van Berkel, F. P. F., Christie, G. M., van Heuveln, F. H. and Huijsmans, J. P. P., Reduced temperature operation of SOFC at ECN. In Proceedings of the 4th International Symposium on Solid Oxide Fuel Cells, ed. M. Dokiya. The Electrochemical Society, Pennington, NJ, 1995, pp. 1062–1071.
The importance of Mn-oxide for chemical reaction between La0.85Sr0.15MnO3 and YSZ
- C Clausen
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- J Bilde-Sorensen
- A Horsewell
Clausen, C., Bagger, C., Bilde-Sorensen, J. and Horsewell, A., The importance of Mn-oxide for chemical reaction between La 0.85 Sr 0.15 MnO 3 and YSZ. In Proceedings of the 14th Risø International Symposium on Materials Science, ed. F. W. Poulsen, J. J. Bentzen, T. Jacobsen, E. Skou and M. J. L. Østergard. 1993, pp. 237–243.
Contribution à l'Etude de La1-xSrxMnO3 comme matériau d'électrode à oxygène à haute température
- A Hammouche
Hammouche, A., Contribution a` l'Etude de La 1Àx Sr x MnO 3 comme mate´riau d'e´lectrode a`oxygène a` haute tempe´rature. PhD thesis, Institut Polytechnique National de Grenoble (F), 1989.
Performance of reduced temperature SOFC-stacks Solid Oxide Fuel Cell Symposium
- N Q Minh
- K Montgomery
Minh, N. Q. and Montgomery, K., Performance of reduced temperature SOFC-stacks. In Proceedings of the 5th International. Solid Oxide Fuel Cell Symposium, ed. U. Stimming, S. C. Singhal, H. Tagawa and W. Lehnert. The Electrochemical Society, Pen-nington, NJ, 1997, pp. 153–160;
Performance and characterisation of anode-supported cells co-cast with thin 8YSZ
- R Ihringer
- S Rambert
- J Van Herle
Ihringer, R., Rambert, S. and Van herle, J., Performance and characterisation of anode-supported cells co-cast with thin 8YSZ. In Proceedings of the 4th European Solid Oxide Fuel Cell Forum, ed. A. J. McEvoy. Forum Sekretariat U, Bossel, Switzerland, 2000, pp. 241–251.
Ther-modynamic analysis on relation between nonstoichiometry of LaMnO 3 perovskites and their reactivity with zirconia
- H Yokokawa
- N Sakai
- T Kawada
- M Dokiya
Yokokawa, H., Sakai, N., Kawada, T. and Dokiya, M., Ther-modynamic analysis on relation between nonstoichiometry of LaMnO 3 perovskites and their reactivity with zirconia. Denki Kagaku, 1989, 57, 829–837.
Nonstoichiometry of perovskite type oxides LaSrCoO 3
- J Mizusaki
- Y Mima
- S Yamuchi
- K Fueki
- H Tagawa
Mizusaki, J., Mima, Y., Yamuchi, S., Fueki, K. and Tagawa, H., Nonstoichiometry of perovskite type oxides LaSrCoO 3. J. Solid State Chem., 1989, 80, 102–110.
Performance and characterisation of anode-supported cells co-cast with thin 8YSZ
- Ihringer
Thermodynamic analysis on relation between nonstoichiometry of LaMnO3 perovskites and their reactivity with zirconia
- Yokokawa
Production of Sr–LaMnO3 perovskite powder by amorphous citrate process
- Baythoun
Reduced temperature operation of SOFC at ECN
- van Berkel