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Electrochemical devices for energy: Fuel cells and electrolytic cells
Abstract
This chapter is dedicated to some significant applications of membranes in the field of energy, focusing on fuel cells and electrolytic cells. Both electrochemical devices are part of an international effort at both fundamental and demonstration levels and, in some specific cases, market entry has already begun. Membranes can be considered as separators between cathodes and anodes. As fuel cells are extremely varied, with working temperatures between 80°C and 900°C, and electrolytes from liquid to solid passing by molten salts, they are of particular interest for the research and development of new membranes. The situation is quite similar to the case of electrolysers dedicated to water electrolysis. The principal features of these devices will be outlined, with emphasis on the properties of the state-of-the-art membranes and on the present innovations in this area.
... Since alkaline fuel cells usually operate between 70 °C and 120 °C [49], AEMs should have good stability at working temperature. In order to evaluate the thermal stability of AEMs, thermogravimetric analysis (TGA) was performed. ...
... Since alkaline fuel cells usually operate between 70 • C and 120 • C [49], AEMs should have good stability at working temperature. In order to evaluate the thermal stability of AEMs, thermogravimetric analysis (TGA) was performed. ...
In recent years, there has been considerable interest in anion exchange membrane fuel cells (AEMFCs) as part of fuel cell technology. Anion exchange membranes (AEMs) provide a significant contribution to the development of fuel cells, particularly in terms of performance and efficiency. Polymer composite membranes composed of quaternary ammonium poly(vinyl alcohol) (QPVA) as electrospun nanofiber mats and a combination of QPVA and poly(diallyldimethylammonium chloride) (PDDA) as interfiber voids matrix filler were prepared and characterized. The influence of various QPVA/PDDA mass ratios as matrix fillers on anion exchange membranes and alkaline fuel cells was evaluated. The structural, morphological, mechanical, and thermal properties of AEMs were characterized. To evaluate the AEMs' performances, several measurements comprise swelling properties, ion exchange capacity (IEC), hydroxide conductivity (σ), alkaline stability, and single-cell test in fuel cells. The eQP-PDD0.5 acquired the highest hydroxide conductivity of 43.67 ms cm-1 at 80 °C. The tensile strength of the membranes rose with the incorporation of the filler matrix, with TS ranging from 23.18 to 24.95 Mpa. The peak power density and current density of 24 mW cm-2 and 131 mA cm-2 were achieved with single cells comprising eQP-PDD0.5 membrane at 57 °C.
... First fuel cell was discovered 180 years ago and has become extensively studied since that days because of its more environmentally friendly properties than conventional energy sources such as coil or gas [1]. Such devices allow to convert chemical energy into electrical one without pollutant gasses emission [2]. As a fuel, one can distinguish hydrogen [3], methane [4] or alcohol such as methanol, ethanol, glycol and glycerine. ...
... In the case of ethylene glycol, the oxidation process takes place both for non-annealed AuCu electrode as well as annealed AuCu sample (Fig. 3b). The proposed oxidation mechanism of C 2 H 4 (OH) 2 can be found in the literature [24][25][26][27]. The ethylene glycol can be oxidase to oxalate (COO -) 2 , formate (HCOO -) or carbonate (CO 3 2-). ...
In this work, we present the catalytic and photocatalytic activity of AuCu nanostructures obtained on TiO2 nanotubes toward methanol, ethylene glycol and glycerine oxidation. The electrode material is prepared by anodization of Ti foil, thin AuCu layer sputtering and rapid thermal treatment under argon atmosphere. Scanning electron microscopy images confirmed the presence of ordered tubular architecture of TiO2 as well as nanoparticles formed on the surface of the nanotubes. The electrodes were measured using cyclic voltammetry, linear voltammetry and electrochemical impedance spectroscopy in dark and under illumination. Obtained results show a significant current increase: 20 and 90 times higher current density at + 0.3 V versus Ag/AgCl/0.1 M KCl after glycol and glycerine addition, respectively. Moreover, a higher current toward alcohol oxidation was registered for thermally annealed samples than for non-annealed ones. Reported studies demonstrate deep insight into the electrical properties of AuCu-modified titania materials.
Graphical abstract
... Consequently, heat management of the TIMs has been a concern. The use of thermally conductive fillers in polymer matrix composites presents a valuable solution for enhancing the thermal properties of gaskets or TIMs at high working temperatures and performing as intended [10]. ...
In the study, a thermoplastic polyurethane composite is formulated and proposed as a gasket used in energy storage technology and energy applications. Due to the high preparation cost of thermally conductive composite gaskets, the composite materials were prepared through inexpensive solution casting and monitored in their thermal conductivity, mechanical properties and morphology. The specimens were also tested in a fluid resistance test and a hot water immersion test. The thermal conductivity of the proposed composite gaskets is in the range of 0.1–0.2 Wm–1K–1. An increase in ZnO loading enhances shore A hardness and Young’s modulus whereas it decreases in %elongation at break. However, tensile strength and tear strength remain unaffected. Scanning electron microscope (SEM) images and SEM combined with Energy Dispersive X-ray analysis (EDX) reveal that the prepared composites demonstrate enhanced thermal conductivity, attributed to a higher filler content and minimized distances between conductive particles. With thicknesses ranging from 1.40 to 1.85 mm, their physical appearance, weight loss and thermal conductivity were not significantly changed after fluid immersion and water immersion at 70 °C. Consequently, the composite samples developed in the study are proposed as promising candidates for use in energy storage technologies and related applications.
... Equations [7,8] have been utilized to determine the refractive index (n) and extinction coefficient (k) values, which are employed to assess material's pellucidity and absorption of incident photons. According to Fig. 7(a), maximum values of refractive index for Sr 2 ZnWO 6 and Sr 2 CoWO 6 are 2.9 and 4.9 at energy 3.06 eV and 0.17 eV has been observed. ...
Double perovskite is a potentially useful material for producing green energy and is thought to meet the necessary criteria for addressing energy shortages. That is why studies into these oxides have potential uses in the fields of optoelectronic technologies. In our present work, we have explored the structural, electronic, and optical properties of the double perovskites Sr2XWO6 (X = Co, Zn) using a first-principle study. Band structure and total density of state analysis shows that Sr2ZnWO6 has wider direct energy gap of 2.75 eV for both spin up and spin down configuration. While, Sr2CoWO6 has slightly reduced indirect energy band gap of 2.06 eV for spin up (↑) and 0.71 eV for spin down (↓) configuration. The dielectric function, absorption coefficients, reflectivity, and refractive index are used to analyze optical characteristics. The optical properties reveal that Sr2CoWO6 has shown much larger optical conductivity and electromagnetic radiation absorption in the UV and visible regions and a minimum value of reflectivity and energy loss function, which make it a suitable compound for optoelectronic applications. Our findings can be beneficial for further experimental research aimed at assessing Sr2XWO6 (X = Co, Zn) in spintronics, solar cell and optoelectronic device applications.
... While the AFC-based CHP system showed similar total efficiency as the other technologies, its thermal efficiency was not as good. Since a building skin component will be created in the upcoming study, its sensitivity to CO 2 [113] makes it less than ideal for use in environments exposed to unavoidable contamination. ...
The integration of distributed renewable energy technologies (such as building-integrated photovoltaics (BIPV)) into buildings, especially in space-constrained urban areas, offers sustainable energy and helps offset fossil-fuel-related carbon emissions. However, the intermittent nature of these distributed renewable energy sources can negatively impact the larger power grids. Efficient onsite energy storage solutions capable of providing energy continuously can address this challenge. Traditional large-scale energy storage methods like pumped hydro and compressed air energy have limitations due to geography and the need for significant space to be economically viable. In contrast, electrochemical storage methods like batteries offer more space-efficient options, making them well suited for urban contexts. This literature review aims to explore potential substitutes for batteries in the context of solar energy. This review article presents insights and case studies on the integration of electrochemical energy harvesting and storage into buildings. The seamless integration can provide a space-efficient source of renewable energy for new buildings or existing structures that often have limited physical space for retrofitting. This work offers a comprehensive examination of existing research by reviewing the strengths and drawbacks of various technologies for electrochemical energy harvesting and storage, identifying those with the potential to integrate into building skins, and highlighting areas for future research and development.
... Fuel cells can convert the chemical energy of H 2 -based fuel gases directly to electrical energy via an electrochemical process [109,110]. Sharing the basic operating principle based on redox reactions in an electrode-electrolyte assembly, a vast range of available fuel cell technologies have been developed in terms of constituent materials (alkaline solutions, polymeric membranes, solid ceramic oxides, and molten carbonate electrolytes), operating temperatures (low-temperature fuel cells between 60 and 100 ∘ C and high-temperature fuel cells between 600 and 900 ∘ C), and operating fluids (pure H 2 , methanol, hydrocarbon fuel reformate, etc.). Different fuel cell technologies provide different operating envelopes in terms of operating temperature, current/power density ranges, dynamic response, fuel flexibility, among others [111,112]. ...
Hydrogen as an energy vector is seen as a fundamental enabler to the energy transition toward a low‐carbon energy future not only from the power perspective but also from a primary energy one. In fact, not only is it conceivable as an electricity storage method (Power‐to‐X‐to‐Power) that can contribute to the safe increase of penetration stochastic renewable electricity to the grid but it also represents a versatile cross‐vector medium enabling the deep decarbonization of non‐electrified hard‐to‐abate sectors (renewable fuels, sector integration, mobility, etc.). In this context, great political and economic interest has risen related to the deployment of hydrogen technologies in the past few years, leading most key players – both industries and institutions – to include hydrogen technologies in national industrial strategies and development programs. In this chapter – after a brief overview of the state of the art of the main hydrogen technologies (declined for each section of the value chain) – an application‐driven analysis of what will be the foreseen role of hydrogen technologies in future integrated energy systems is provided, considering a wide range of applications such as energy storage, grid flexibility services, renewable feedstocks for heavy industries, and fuel cells for both stationary μ‐CHP and automotive applications. Ultimately, a list of worldwide key breakthrough projects of the period 2000–2020 is provided to show the history and development of hydrogen technology toward market maturity.
... Fuel cells (FCs) are highly efficient electrochemical devices converting the chemical energy of the fuel to electrical energy without intermediate stages and gaining usage Environmental Technologies to Treat Rare Earth Elements Pollution as portable power sources (Cassir et al., 2013). FCs are more eco-friendly in comparison with thermal engines and have the significant advantage of unlimited sources of fuel and oxidant (Shao et al., 2016). ...
Rare earth elements (REE) have applications in various modern technologies, e.g., semiconductors, mobile phones, magnets. They are categorized as critical raw materials due to their strategic importance in economies and high risks associated with their supply chain. Therefore, more sustainable practices for efficient extraction and recovery of REE from secondary sources are being developed.
This book, Environmental Technologies to Treat Rare Earth Elements Pollution: Principles and Engineering: presents the fundamentals of the (bio)geochemical cycles of rare earth elements and which imbalances in these cycles result in pollution.overviews physical, chemical and biological technologies for successful treatment of water, air, soils and sediments contaminated with different rare earth elements.explores the recovery of value-added products from waste streams laden with rare earth elements, including nanoparticles and quantum dots.
This book is suited for teaching and research purposes as well as professional reference for those working on rare earth elements. In addition, the information provided in this book is helpful to scientists, researchers and practitioners in related fields, such as those working on metal/metalloid microbe interaction and sustainable green approaches for resource recovery from wastes.
ISBN: 9781789062229 (Paperback)
ISBN: 9781789062236 (eBook)
ISBN: 9781789062243 (ePUB)
... Fuel cells (FCs) are highly efficient electrochemical devices converting the chemical energy of the fuel to electrical energy without intermediate stages and gaining usage Environmental Technologies to Treat Rare Earth Elements Pollution as portable power sources (Cassir et al., 2013). FCs are more eco-friendly in comparison with thermal engines and have the significant advantage of unlimited sources of fuel and oxidant (Shao et al., 2016). ...
Rare earth elements (REE) have applications in various modern technologies, e.g., semiconductors, mobile phones, magnets. They are categorized as critical raw materials due to their strategic importance in economies and high risks associated with their supply chain. Therefore, more sustainable practices for efficient extraction and recovery of REE from secondary sources are being developed.
This book, Environmental Technologies to Treat Rare Earth Elements Pollution: Principles and Engineering:
presents the fundamentals of the (bio)geochemical cycles of rare earth elements and which imbalances in these cycles result in pollution.
overviews physical, chemical and biological technologies for successful treatment of water, air, soils and sediments contaminated with different rare earth elements.
explores the recovery of value-added products from waste streams laden with rare earth elements, including nanoparticles and quantum dots.
This book is suited for teaching and research purposes as well as professional reference for those working on rare earth elements. In addition, the information provided in this book is helpful to scientists, researchers and practitioners in related fields, such as those working on metal/metalloid microbe interaction and sustainable green approaches for resource recovery from wastes.
... The benefits of PEM are high efficiency, high power density, reduced corrosion, high operational [67][68][69]. Nowadays, PEMFCs became one of the valuable chemical engineering technology due to their capability of quick start-up and lowtemperature operation [70][71][72]. Finally, the PEMFCs are also environmental friendly as there is no emission of harmful gases like oxides of sulfur and nitrogen, which are environmentally benign [73][74][75]. ...
Polymer membranes are emerging substrates for industrial applications like power solutions, toxic metal ion removal and drug delivery technologies. Among all types of membranes polymer electrolyte membranes (PEMs) are current interest, due to their physico-chemical interaction with the guest molecules. PEMs are capable to transport or permeate, adsorb and delivery of molecules, ions and other required reagents. This chapter provides basic concepts as well as the progress with regard to PEMs based science and technology of fuel cells and drug delivery.
... In the following section the laboratory practice activities are presented, reporting graphs of real measurements obtained during the testing phase of the remote laboratory facility. The obtained results are in line with the expected behaviour of the components and literature references for solar cells (Duffie and Beckman, 2013) and H2 systems (Cassir et al., 2013). The laboratory practice is developed in seven steps as follows: ...
This paper presents a prominent e-learning tool that is part of deliverable packages of Hy2Green Project (Ref. 2017-1-ES01-KA203-038302). The aim of the project is to develop an online training course that can help to improve new professional profiles in hydrogen technologies, in line with the energy transition model in Europe. As part of this training course and as result of a team collaboration, a remote laboratory based on hydrogen technology has been designed and implemented. Through the online platform, students from every part of the world can access remotely and in real-time, to a real laboratory built from a scaled green-hydrogen production plant. The green-hydrogen production plant has, in addition to hydrogen production and storage subsystems, a fuel cell, through which electricity is generated with the stored hydrogen. The developed remote laboratory offers technological and educational improvements. From the technological point of view, it allows handling a real installation, throughout the entire energy conversion process, being able to carry out laboratory tests, to characterize the different components. This remote laboratory is proposed as a multidisciplinary tool, where students develop their skills in automatic control, system modelling and renewable energy management. On the other side, from the educational point of view, this proposal contributes to democratization of education. That is nowadays equipment related to hydrogen technology is not cheap, so this implies that not all educational centres cannot afford to have a hydrogen laboratory. The remote laboratory presented in this work offers the possibility to carry out laboratory practices to whatever the student and the university are.
... High temperature conditions allow the use of non-noble materials at the electrodes (e.g., Ni) instead of noble materials (e.g., Pt) which are used in low temperature fuel cells [14,15], although operating conditions are more difficult to manage, materials are subject to more stressful thermo-mechanical loads, and dynamic capability is limited [14,16]. In addition, high temperature fuel cells are more robust regarding carbonaceous fuels (especially for CO poisoning [4,13,17]), being able to process hydrocarbon fuels (e.g., CH4, bio/syngas mixtures, natural gas, etc.) thanks to the internal reforming occurring at such temperatures with Ni catalyst presence-provided that a suitable steam-to-carbon ratio is observed [18][19][20]. The sum of such characteristics allows Solid Oxide Fuel Cells (SOFCs) to represent a suitable technological coupling option for Combined Heat and Power (CHP) applications fed by conventional and unconventional fuels (e.g., natural gas, bio-syngas mixtures, etc.) positioning SOFCs as a key component of a low-carbon energy matrix and closing a high efficiency, zero-emission energy cycle with minimal emissions [21][22][23]. ...
Solid Oxide Fuel Cells are a promising technology for Solid Oxide Fuel Cells (SOFC) are a promising technology For high-efficiency electrochemical conversion of a vast range of fuel gas mixtures, thigh operating temperature conditions (650–900 °C) represent a challenge both at system level and at laboratory testing level, in terms of material properties and performance dynamics. In this work a detailed procedural analysis is presented for an innovative all-ceramic compact SOFC test rig and first experimental testing results are reported in terms of polarization curves obtained under parametric variation of operating conditions (H2 content, air ratio λ and temperature) and short-term voltage stability test under load (140 h at 0.3 A/cm²). The electrochemical characterization results confirm the validity of the used all-ceramic cell holder, showing excellent cell performances in terms of polarization. H2 content has the most impact on SOFC performance, followed by temperature and finally air ratio, whose impact in the analyzed range is hardly seen. From the short-term stability test, the test bench setup reliability is demonstrated, showing no significant performance degradation after 140 continuous hours under load, which confirms the high quality and reproducibility of the results.
... In the following section the laboratory practice activities are presented, reporting graphs of real measurements obtained during the testing phase of the remote laboratory facility. The obtained results are in line with the expected behaviour of the components and literature references for solar cells (Duffie and Beckman, 2013) and H2 systems (Cassir et al., 2013). The laboratory practice is developed in seven steps as follows: ...
This paper presents a prominent e-learning tool that is part of deliverable packages of Hy2Green Project (Ref. 2017-1-ES01-KA203-038302). The aim of the project is to develop an online training course that can help to improve new professional profiles in hydrogen technologies, in line with the energy transition model in Europe. As part of this training course and as result of a team collaboration, a remote laboratory based on hydrogen technology has been designed and implemented. Through the online platform, students from every part of the world can access remotely and in real-time, to a real laboratory built from a scaled green-hydrogen production plant. The green-hydrogen production plant has, in addition to hydrogen production and storage subsystems, a fuel cell, through which electricity is generated with the stored hydrogen. The developed remote laboratory offers technological and educational improvements. From the technological point of view, it allows handling a real installation, throughout the entire energy conversion process, being able to carry out laboratory tests, to characterize the different components. This remote laboratory is proposed as a multidisciplinary tool, where students develop their skills in automatic control, system modelling and renewable energy management. On the other side, from the educational point of view, this proposal contributes to democratization of education. That is nowadays equipment related to hydrogen technology is not cheap, so this implies that not all educational centres cannot afford to have a hydrogen laboratory. The remote laboratory presented in this work offers the possibility to carry out laboratory practices to whatever the student and the university are.
... Although direct conversion to electricity could place the basis for an effective clean coal power technology, the research has been largely frustrated by a lack of developmental progress for many years due to issues such as poor coal electrochemical reactivity, ash accumulation, sulfur contamination and materials corrosion [21,22]. However, the relatively rapid improvement in molten carbonate and solid oxide fuel cell technologies over the past two decades has contributed to solve some technical challenges related to design and operational aspects of early types of solid-fed fuel cells [23] and stimulated a significant return of research interest on this topic as highlighted by numerous journal articles ( [21,24e45]), book chapters ( [2,3,46,47]) and review studies ( [29,48e53]) that have been published over the past few years. Recent works carried out by Cooper, Selman and co-workers on carbon particulate reactivity in molten carbonates have been a further stimulus to the new research interest [41,42,54]. ...
Unprecedented interest for clean and sustainable energy innovation has recently stimulated a return of attention on molten alkali carbonate salts not only for traditional use as electrolyte and high temperature reaction media but also as innovative energetic material for advanced applications in hybrid fuel cell systems and high-temperature CO2 gas separation processes. The main focus of this literature review is on examining novel and emerging molten carbonate applications in energy sectors beyond the well-assessed and mature domain of the Molten Carbonate Fuel Cells. In general, a number of advanced processes and highly functional materials are currently under investigation involving molten carbonates in a key role, suggesting a high potential of these salt systems for the future development of sustainable energy technologies. Current research activities can be grouped into three main energy research areas related to generation/conversion/storage of energy, materials and manufacturing processes, hot gas processing and gasification technologies. As already analyzed in Part I of this work, notable features of molten carbonates include their chemical stability, safety and optimal performance under a wide range of moderate (500-600°C) and moderate-to-high temperature (600-800°C) conditions. Thanks to these peculiar aspects, molten carbonate processes can be ideally integrated with solar energy sources for maximum sustainable level of use and with broad development prospects in the storage of solar energy and solar-to-chemical conversion systems. This view is confirmed, for example, by a series of extensive studies that has recently investigated novel solar-to-chemical energy conversion strategies based on a molten carbonate electrolysis process for solar production of fuels and other important chemical products, including iron and cement. In the last part of this work, several directions and opportunities for future research and studies on molten carbonates are suggested.
div class="section abstract"> Inadequately designed flow field layouts in bipolar plates within Proton Exchange Membrane fuel cells (PEMFCs) may lead to ineffective water removal and impede reactant transport. This work examines the conventional flow channel designs like that parallel, pinhole, spiral, maze, leaf-like, modified serpentine with two bypass channels, and modified serpentine with four bypass channels in bipolar plates of fuel cells and implements modifications to certain designs to alleviate pressure drops within the flow channels using computational fluid dynamics (CFD) analysis. These designs are optimized by changing different parameters such as size of the channel and rib width utilizing Taguchi L27 standard orthogonal array. The resultant reduction in pressure drop is anticipated to enhance the overall performance of the fuel cell. The optimal flow field design of bipolar plates (Graphite and Aluminum) are manufactured using CNC milling. Tests evaluating surface roughness, contact angle, and corrosion resistance are conducted to assess and compare the performance of these plates. After thorough testing and evaluation, Aluminum showed inferior results compared to Graphite in two key areas: Corrosion rate and Contact angle. Consequently, anodizing was performed on Aluminum to enhance its contact angle and corrosion resistance. The anodized aluminum demonstrated superior performance among the tested materials.
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Nanofibers are advanced materials widely used in fuel cell applications owing to their superior characteristics of large surface area and porosity. Aligned nanofibers, a next-level development in nanofibers, is a promising approach for implementation in fuel cell applications, considering that they enhance specific properties compared to randomly orientated structures. This review presents the current strategies for fabricating aligned nanofibers and explores various methods to obtain targeted assemblies. These methods include increasing the speed of the rotating collector, applying multiple electric fields, and using engineering-defined collectors, for instance, wiring drums, patterned strips, frame shapes, rotating discs, rotating jets, and guide column arrays. Moreover, the rationality behind why this structure can improve fuel cell performance is elaborated, which includes enhanced conductivity, improved mass transport, structural durability, and reduced water flooding. The prospects and challenges of implementing aligned nanofibers in fuel cells are also included.
Energy underlies the human development and welfare. Today energy depends on combustion of fossil fuels (coal, natural gas, oil) sources. These sources have not only led to severe environmental issues because it emits greenhouse gases, they are rapidly depleted due to their enormous consumption. For several years’ numerous technologies have been developed to address the fossil fuel depletion and greenhouse gases emission from the non-renewable in order to constantly supply energy to the people and industries. However, the challenge of being able to store energy generated and utilize it later is a matter of importance when resolving energy problems persists. New materials, particularly perovskites offer a great advantage to be utilized as a possible host or carriers for energy applications. The impact of defect on the material properties and influence of defects as material for energy application is described. The use of perovskites oxides for effective electrocatalysis in hydrogen evolution reactions, photocataysis, photovoltaic solar cells, electrocatalysis, solid oxide fuel cells, supercapacitors and metal-air batteries, are also included. This review covers the latest progress on perovskite oxides as electrochemical energy materials.
In fuel cell technologies, low-temperature proton exchange membrane fuel cells (LT-PEMFC), high-temperature proton exchange membrane fuel cells (HT- PEMFC), and direct methanol fuel cells (DMFC) are gained significant attention as a promising energy system for practical applications. The developments of cost-effective membrane materials with excellent physicochemical properties are indispensable for replacing the high cost of commercial membranes and achieving the higher performance of fuel cell systems. This review focuses on the developments and modifications of cost-effective poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a cation exchange membrane for LT-PEMFC, HT- PEMFC and DMFC. Notably, this review bridges the understanding of PPO based membranes, current advancements, structure, physicochemical properties and fuel cell performances. Progressive developments and a systematic overview of PPO-based membrane developments are explained in detail in terms of functionalization, blend, composite, acid-base, cross-linking, copolymerization, coated and reinforcement. Moreover, the changes in physicochemical properties and fuel cell performances in the membrane are deeply reviewed. Additionally, the utilization of PPO based membranes in different kinds of redox flow battery systems are reviewed. Overall, this review provides an exclusive vision and perspectives to develop the PPO based advanced, cost-effective, and high-performance membranes for fuel cell technologies and redox flow battery systems.
Lignin is a prospective resource for renewable commodity organic chemicals and fuels. In the scheme of a sustainable biorefinery, lignin valorization is essential for enhancing the economic feasibility of the overall biomass transformation processes. Electrocatalysis and electrochemical processes are expected to play a major role in biomass valorization due to the possibility of using renewable electricity sources for in situ production of ‘green’ H2 and other reagents that are necessary for biomass conversion. Recent advances in the electrocatalytic hydrogenation and hydrogenolysis of lignin derivatives, including oxygenated aromatic compounds, suggest promising pathways for the synthesis of industrially relevant chemicals, such as ketone-alcohol (KA) oil, the mixture of cyclohexanone and cyclohexanol for the production of Nylon polymers. This review presents the prospect of electrocatalytic reduction approaches for a mild synthesis of lignin-based chemicals with emphasis on the potential applications of high current density electrolysis. Feasible electrocatalytic oxidation strategies for lignin depolymerization are also summarized, highlighting the fundamental differences between the electrochemical reductive and oxidative routes. Finally, challenges and opportunities for future development of the electrocatalytic pathways for lignin valorization are discussed.
Atomic layer deposition (ALD) offers the opportunity to design and engineer surface structures at the atomic scale, targeting improved performance of not only fuel cells but also electrochemical sensors, electrolyzers, and pumps. Two types of high-temperature fuel cells, operating between 600 and 1000 °C, are developed: molten carbonate fuel cells (MCFCs) and solid oxide fuel cells (SOFCs). ALD is becoming an important tool in the new generation of fuel cells, including SOFCs and, probably in the near future, MCFCs, and other related techniques. MCFC cathode suffers corrosion and dissolution in molten carbonates. Corrosion of stainless steel bipolar plates is another important issue with regard to durability and performance of MCFCs. One of the most promising techniques to improve the dissolution and corrosion resistance of cathode and bipolar plates is through protective coatings of metal oxides.
In a changing world, the paradigm of energy and environment is also evolving and the importance of hydrogen and fuel cells is progressively increasing. This evolution is slow but sure because fuel cells play already an important role in a transition phase, where fossil fuels are still predominant, and also for the future where renewable energies will meet sufficient efficiency for replacing old energetic sources. The aim of this chapter is to give a rapid and up&;#x02010;to&;#x02010;date vision on fuel cells and on their potentialities. We will first introduce some general aspects, principles, variety and main features of fuel cells. We will also depict specific challenges, in particular on materials, for each family of fuel cells. We will insist, in particular, on new concepts and ideas to improve or fully transform the present systems. We will finally say a few words on the growing worldwide market in the field of transport and stationary applications.
The efficacy of added freestanding and silica-supported metal (Pt, Pd, Ag, and Au) nanoparticles in mitigating polymer electrolyte membrane (PEM) degradation in an operating fuelcell was investigated. The metal nanoparticles to be added were chosen based on their ability to scavenge free radicals, as confirmed through ex situ measurements using a model free radical 1,1-diphenyl-2-picrylhydrazyl as a test species. Composite membranes were prepared by adding 3 wt% of the freestanding or supported metal nanoparticles to Nafion®. Membraneelectrodeassemblies prepared using these membranes were subjected to accelerated degradation tests to determine the fluoride emission rate (FER), a key measure of the macroscopic rate of PEMdegradation in an operating fuelcell. The results were as follows: the addition of Ag, Pt, Pd and Au freestanding nanoparticles lowered FER by 35%, 60%, 80% and 90%, respectively, when compared with the recast Nafion® membrane (control). In the case of silica-supported nanoparticles, more modest reductions were achieved: 40% and 60% in the case of Au on SiO2 and Pd on SiO2, respectively. Ag or Pt on SiO2 resulted in similar FER values as the control. These results suggest that the addition of selected metal nanoparticles with radical scavenging abilities is a promising approach to mitigate PEMdegradation in an operating fuelcell.
The La10−x(SiO4)6O3−1.5x
(9.33 ≤ 10−x
≤ 9.73) apatite series has been prepared and hexagonal single phases were obtained in a narrow compositional range (9.33 ≤ 10−x
≤ 9.60). The room temperature crystal structure of La9.55(SiO4)6O2.32 has been determined from joint Rietveld refinement of neutron and laboratory X-ray powder diffraction data: a
= 9.7257(1)
Å, c
= 7.1864(1)
Å, V
= 588.68(1)
Å3, Z
= 1, RwpN
= 3.2%, RwpX
= 7.7%, RFN
= 1.8%, RFX
= 1.9%. An interstitial site for the extra-oxygen has been determined in the position very recently predicted in a theoretical study using atomistic simulations. The high temperature crystal structures have been obtained from neutron powder diffraction, NPD, collected at 773 and 1173 K showing the thermal evolution of this interstitial site. Previously reported neutron data for La9.60(GeO4)6O2.40 have also been re-analysed establishing the existence, and thermal evolution, of this interstitial site. The electrical results suggest that the samples are oxide ion conductors. The plots of the imaginary parts of the impedance, Z″, and the electric modulus, M″, vs. log(frequency), possess maxima for both curves separated by two decades in frequency. Bulk conductivities have been obtained from the fitting of the complex impedance spectra with the appropriate equivalent circuit. Bulk activation energies have been determined from two Arrhenius plots, one representing the bulk conductivities and the other representing the frequencies of the modulus peak maxima, fmax(M″). A comparative discussion of the two series, La10−x(TO4)6O3−1.5x
(T = Si, Ge), is given.
Synthesis by means of a modified Pechini method of pure and alkaline-doped (Na, K and Rb) La2Mo2O9
(LAMOX) is presented. The electrical conductivity of LAMOX prepared by this method is completely analogous to that of the solid state prepared material. Doping with K and Rb hinders the α
→
β phase transition found in the pure and Na-doped material around 580 °C. Electrical measurements as a function of pO2 shows that LAMOX has a mainly ionic conductivity down to 10−18 atm. The electrical conductivity of the doped samples is close to that of the pure molybdate for temperatures higher than about 600 °C, while for K- and Rb-doped samples the conductivity is higher for lower temperatures, as a consequence of the absence of the phase transition. Finally, a non-Arrhenius behaviour is observed for all the investigated samples and correlated, at a first approximation, to the structural peculiarities of the LAMOX family.
The slow dissolution of the lithiated nickel oxide cathode represents one of the main causes of performance degradation in molten carbonate fuel cells (MCFC). Two main approaches were studied in ENEA laboratories to overcome this problem: protecting the nickel cathode covering it by a thin layer of a material with a low solubility in molten carbonate and stabilizing the nickel cathode doping it with iron and magnesium.Among several materials, due to its low solubility and good conductivity, lithium cobaltite was chosen to cover the nickel cathode and slow down its dissolution. A nickel electrode covered with a thin layer of lithium cobaltite doped with magnesium, was fabricated by complex sol–gel process. To simplify electrode preparation, no thermal treatments were made after covering to produce lithium cobaltite, and during the cell start-up LiMg0.05Co0.95O2 was obtained in situ.To stabilize the nickel cathode, metal oxides Fe2O3 and MgO were chosen as dopant additives to be mixed with NiO powder in a tape-casting process (Mg0.05Fe0.01Ni0.94O).On the prepared materials TGA analysis, morphological analysis by scanning electron microscopy (SEM–EDS) and electrical conductivity measurements were carried out.A conventional nickel cathode, the nickel cathode covered by lithium cobaltite precursors and the nickel cathode stabilized by iron and magnesium oxides were each tested in a 100cm2 fuel cell.Polarization curves and internal resistance (iR) measurements were acquired during the cell lifetime (1000h) and the effect of gas composition variation on the cell performance was studied.From a comparison with the conventional nickel cathode it can be observed that the new materials have similar performance and show a good potential stability during the cell operating time. From the post-test analysis both the nickel cathode covered by lithium cobaltite and the nickel cathode doped with iron and magnesium seem to succeed in reducing nickel dissolution.
The author of this unique handbook on fluorinated ionomers is also the inventor of the first commercial product known as Nafion? (DuPont). The book covers partially fluorinated and perfluorinated polymers containing sufficient ionic groups to dominate the transport properties of the polymer. The emphasis of this book is on the practical aspects of working with fluorinated ionomers. It is intended to help the scientist and engineer in the preparation, fabrication, use, and study of these products as well as in the development of new applications and compositions. Extensive coverage has been given to perfluorinated ionomers because of the practical importance of this group of polymers. Commercial products such as Nafion?, Aciplex? (Asahi Chemical) and Flemion? (Asahi Glass) are fluorinated ionomers have been discussed in detail. Whether you need information about use of fluorinated ionomers in fuel cells, batteries, chlor-alkali cells, sensors, fabrication techniques, or commercial products you will find it in this valuable handbook. © 2008 William Andrew Inc. Published by Elsevier Inc. All rights reserved.
PRIMEA® membrane electrode power assemblies have been available from W. L. Gore & Associates, Inc. (Gore) since 1995, when Gore introduced the 5000 series based on the GORE-SELECT® composite membranes. In order to provide the highest power density power assembly, a second generation PRIMEA® membrane electrode power assembly (series 5510) was introduced in 1997. Both series 5000 and 5510 power assemblies were designed for hydrogen/air applications. A third generation of PRIMEA® membrane electrode power assemblies is now available for operations with reformate fuel streams. All Gore MEAs have been made available with complementary components such as integral gasketing and gas diffusion media, to maximize product performance and durability. In this publication, we explore the selection of MEA characteristics required in common applications. Performance data will be provided on a range of PRIMEA® power assemblies under conditions which should be relevant to selection and design criteria typically encountered in fuel cell stack and system development. In addition, examples of successful field demonstrations of PRIMEA® power assemblies will be shown in various applications, demonstrating the scope for system differentiation utilizing one family of MEA products. This paper is divided into four sections; the first three exploring specific requirements of portable, stationary, and transportation applications, and the fourth section discusses general product issues, such as quality assurance and manufacturing requirements, as well as ancillary components and associated technical support.
The protonic conductivity of polybenzimidazole (PBI) in various electrolytes was systemically studied. It was shown that blank PBI is a protonic insulator. Its conductivity measured in acid electrolyte is ∼10-10 to 10-9 S- cm-1. The same conductivity was obtained for measurements taken on PBI used in a PEM fuel cell configuration. After doping in H2SO4, HCl, HNO3, HClO4 or H3PO4 it exhibited high protonic conductivity. The conductivity depends on the type of doping acid agent and its concentration. The highest conductivity obtained (i.e. 0.0601 S · cm-1 for PBI doped with 16 mol/L H2SO4) was as good as that of Nafion® 117. The conductivity changes in the order H2SO4 > H3PO4 > HClO4 > HNO3 > HCl for high concentrations (11-16 mol/L) of the doping acid. It was shown that the high conductivities of PBI films were obtained after doping them with H2O4, H3PO4 or HClO4. These high values make them suitable candidates for fuel cell applications. From these results, it was shown that the conductivity of blank PBI in acid media must be measured before the film is doped with acid.
The ceria-based dual-phase composites have been recently developed as functional electrolytes successful for intermediate and low temperature solid oxide fuel cell applications. These composite materials showed many unique advantages over the conventional single-phase electrolytes, such as superionic conduction in two-phase interfaces, dual proton and oxygen ion conduction resulting in extremely high ion conductivity and high current outputs in fuel cell and other applications, e.g. electrolysis. Interfacial superionic conduction is a characteristic for high conducting dual-phase composites. The composite approach can combine or integrate multi-ion functions, typically, dual H+ and O2- conduction together to enhance the material conductivity and device performance. Dual or hybrid H+ and O2-conduction is based on a consideration that both proton (H+) and oxygen ion (O2-) are the fuel cell source ions. Proton conduction is important for LTSOFCs since it can be activated easier than oxygen ions in the low temperature (LT, 300- 600°C) region. The superionic conduction, dual phase proton and oxygen ion transport make significant conduction and electrical contributions for electrochemical devices. This paper makes a review on these recent studies.
W. R. Grove, professor of experimental philosophy in the London Institution, shared his views on a particular experiment in a letter to R. Phillips in the London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science. The experiment involved a galvanometer being permanently deflected when connected with two strips of platina covered by tubes containing oxygen and hydrogen. He said that he considered surrounding the platina foil with spongy platina precipitated in the usual way by muriate of ammonia. This was suggested to him by the known action of spongy platina on mixed gas, which would expose a considerable surface of metal and liquid to the action of the gases by its capillary action. He caused a series of fifty pairs to be constructed where ox denoted a tube filled with oxygen, hy denoted a tube filled with hydrogen, and the dark line in the axis of the tube platinized platina foil, which was one-fourth of an inch in width in the battery constructed by him for the experiment.
The hydrogen oxidation reaction in (62 + 38) mole percent (Li + K)CO3 has been studied at Au, Ag, Cu, Pt, Ir, Pd, Ni, Co, and Fe electrodes by using cyclic voltammetry, ac impedance, potential step, and chronocoulometric methods. Impedance data were analyzed by computer fitting with an equivalent circuit, taking hydrogen adsorption into account. The chronocoulometric method was employed to determine the stoichiometric number ν using a new technique described in this paper, and the value obtained was ν = 2. The apparent transfer coefficient, α, and exchange current density were also determined from an Allen-Hickling plot, and found to be α = 0.1 - 0.25 for Au, Ir, and Ag, and α = 0.5 for Ni and Pt. The concentrations and diffusion coefficients of the reactant and the product species, including the diffusion process of hydrogen dissolved in the Ni lattice, were estimated from the Wilke-Chang equation. Based on these results, a detailed reaction mechanism is proposed in this paper.
The thermal, mechanical and electrochemical characterisation of sitlfonated polyetherketone, including fuel cell tests in hydrogen/ oxygen and hydrogen/air are described. In thermogravimetric analysis, PEEK-S membranes lose water up to 150°C and degradation of the sulfonic acid groups takes place at ca. 240°C. Thermomechanical analysis of a PEEK-S membrane of 60 μm thickness and equivalent weight 625 g/mole shows that the membrane undergoes a shrinkage of 1.5 % up to 140°C. Reversible elongation of 0.6 % occurs thereafter up to 180°C. The conductivity, measured by impedance spectroscopy, on non-reinforced and on woven-polymer reinforced PEEK-S, is reported as a function of temperature and of relative humidity (RH), and compared with that of Nafwn®-117. At 100°C and 100% RH the conductivity of PEEK-S is 2 5.10-2 Scm-1 (depending on thermal history), increasing to 0.11 Scm-1 at 150°C. Polarisation characteristics of a non-reinforced PEEK-S membrane of 18 ®m thickness at temperatures up to 110°C under conditions of hydrogen/air and hydrogen/oxygen are compared. The results of fuel cell (H2-O2) tests on composite, reinforced membranes are reported.
Cerium and manganese ions are very effective reversible scavengers of •OH in an operating PFSA-based PEM fuel cell. The use of these ions in very small quantities can reduce the fluoride release rate by up to three orders of magnitude relative to an unmitigated sample and thereby afford extremely durable membranes. A chemically rational mechanism that accounts for the remarkable effectiveness of these chemical mitigants is presented.
Les avantages environnementaux des piles à combustible (rendements électrique et énergétique élevés, très faibles émissions de gaz nocifs, faible nuisance sonore, production localisée...) sont des atouts qui deviennent importants pour notre société. Cependant, ils ne sont pas suffisants si les coûts d’investissement sont trop élevés ; c’est sur ce critère que les efforts les plus importants restent à faire pour que cette technologie soit utilisée.
Depuis leur invention en 1839, les piles à combustible ont subi un développement cyclique, le cycle précédent datant des années 1970. Les perspectives d’un développement commercial n’ont jamais été aussi bonnes, par suite des efforts de plusieurs grands groupes industriels et de constructeurs automobiles. Les filières gagnantes seront probablement celles utilisant un électrolyte solide : les PEMFC et les SOFC. Ces deux technologies ont maintenant atteint le niveau de prototype et un début de commercialisation est possible avant 2005. Elles ont toutes les deux une bonne compacité, de bonnes perspectives de réduction de coût et des durées de vie suffisantes (40 000 heures).
"http://www.techniques-ingenieur.fr/base-documentaire/energies-th4/accumulateurs-d-energie-42243210/piles-a-combustible-d3340/
The La 2W 2- xMo xO 9 series
has been synthesized by the ceramic method. An alternative synthesis
using microwave radiation is also reported. La 2W
2O 9 has two polymorphs and the low-temperature
phase ( α) transforms to the high-temperature form ( β) at
1077°C. The influence of the W/Mo substitution in this phase
transition has been investigated by DTA. The β structure for
x≥0.7 compositions can be prepared as single phase at any cooling
rate. The β phase for 0.3≤ x≤0.7 compounds can be prepared as
single phase by quenching, whereas a mixture of α and β
phases is obtained by slow cooling. The W/Mo ratio in both coexisting
phases is different with the β-phase having a higher Mo content.
The x=0.1 and 0.2 compounds have been prepared as mixtures of phases.
The room temperature structure of β-La 2W
1.7Mo 0.3O 9 has been analyzed by the
Rietveld method in P2 13 space group. The final R-factors
were RWP=9.0% and RF=5.6% with a structure similar
to that of β-La 2Mo 2O 9. Finally,
the thermal expansion of both types of structures has been determined
from a thermodiffractometric study. The thermal expansion coefficients
were 2.9×10 -6 and 9.7×10 -6°C
-1 for α-La 2W 2O 9
and β-La 2W 1.2Mo 0.8O
9, respectively.
The main factor governing the oxygen ionic conductivity in apatite-type
La 10-xSi 6-yAl
yO
27-3x/2-y/2 (
x=0-0.33; y=0.5-1.5) is the concentration of mobile interstitials
determined by the total oxygen content. The ion transference numbers,
measured by modified faradaic efficiency technique, vary in the range
0.9949-0.9997 in air and increase on reducing oxygen partial pressure
due to decreasing p-type electronic conduction. The activation energies
for ionic and hole transport are (56-67)±3 kJ/mol and
(57-100)±8 kJ/mol, respectively. Increasing oxygen content leads
to higher hole conduction in oxidizing atmospheres and promotes minor
oxygen losses from the lattice when the oxygen pressure decreases,
although the overall level of ionic conductivity is almost constant in
the p(O 2) range from 50 kPa down to 10 -16 Pa.
Under reducing conditions at temperatures above 1100 K, silicon oxide
volatilization from the surface layers of apatite ceramics results in a
moderate decrease of the conductivity with time. This suggests that the
operation of electrochemical cells with silicate-based solid
electrolytes should be limited to the intermediate-temperature range,
such as 800-1000 K, where the ionic transport in most-conductive apatite
phases containing 26.50-26.75 oxygen atoms per unit formula is higher
than that in stabilized zirconia. The average thermal expansion
coefficients of apatite ceramics, calculated from dilatometric data in
air, are (8.7-10.8)×10 -6 K -1 at 300-1300
K.
The specific conductance of molten carbonate fuel cell electrolyte
layers was examined. Two types of tiles, one prepared by electrophoretic
deposition and one hot-pressed, both 45% LiAlO2 by weight and 55%
lithium pottassium carbonate, with the former being 51% porous with
pores averaging 0.25 microns, were tested. A four probe ac impedance
technique was employed to measure the conductance by inputting an ac
signal and assaying the impedance, which varied 2% over a 1-50 kHz
range. The measurements were performed from room temperature to 800 C.
Sample resistance below the melting point of the carbonate, 496 C, was
5000 ohms, and reduced to 0.1 ohm when the carbonate melted. Trials with
an oxidant gas and a fuel gas revealed that the specific conductance is
independent of the atmosphere.
The effect of the side-chain length (short side chain and long side chain, SSC and LSC, respectively) of perfluorosulfonic acid (PFSA) ionomers on the properties of nanofibers obtained by electrospinning ionomer dispersions in high dielectric constant liquids has been investigated with a view to obtaining electrospun webs as components of fuel cell membranes. Ranges of experimental conditions for electrospinning LSC and SSC PFSAs have been explored, with a scoping of solvents, carrier polymer and PFSA ionomer concentrations, and carrier polymer molecular weight. Under optimal conditions, the electrospun mats derived from SSC and from LSC PFSA show distinct fiber dimensions that arise from the different chain lengths of the respective ionomers. Enhanced interchain interactions in SSC PFSA with low equivalent weight compared to LSC PFSA result in a considerably lower average fiber diameter and a markedly narrower fiber size distribution. The proton conductivity of nanofiber mats of SSC and LSC PFSA with equivalent weights of 830 and 900 g mol−1, respectively, are 102 and 58 mS cm−1 at 80°C and 95% relative humidity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013
In the past years, a major interest has been devoted to decrease the working temperature of solid oxide fuel cells (SOFCs) down to about 700 °C.Apatite materials (La10−xSrxSi6O27−x/2) are attractive candidates for solid electrolytes, with a high ionic conductivity at 700 °C, a chemical and a dimensional stability for a pO2 ranging from 10−25 to 0.2 atm. A perovskite oxide (La0.75Sr0.25Mn0.8Co0.2O3−δ) has been used as a cathode material.Symmetrical cathode/electrolyte/cathode cells were fabricated by stacking layers obtained by tape casting of apatite and perovskite powders and co-sintering at 1400 °C for 2 h in air.Impedance spectroscopy measurements were performed on these cells in order to determine the electrode resistance. It has been shown that the latter decreases with the porosity content of the cathode and with the use of a composite material (apatite/perovskite) instead of a simple perovskite.
Ceria-based composites are developed and considered as potential electrolytes for intermediate solid oxide fuel cell applications (ITSOFC). After giving a survey of the most relevant results in the literature, the structural, thermal and morphological properties of composite materials based on gadolinia-doped ceria (GDC) and alkali carbonates (Li2CO3–K2CO3 or Li2CO3–Na2CO3) are carefully examined. Thermal analyses demonstrate the stability of the composite with very low weight losses of both water and CO2 during thermal cycling and after 168 h ageing. High-temperature and room-temperature X-ray diffraction allowed determining the precise structure of the composite and its regular and reversible evolution with the temperature. The microstructure and morphology of electrolyte pellets, as observed by scanning electron microscopy (SEM), show two-well separated phases: nanocrystals of GDC and a well-distributed carbonate phase. Finally, electrical conductivity determined by impedance spectroscopy is presented as a function of time to highlight the stability of such composites over 1500 h.
We report that the addition of the alkaline-earth carbonates CaCO3, SrCO3 and BaCO3, to an alkali carbonate mixture effectively reduced the solubility of nickel oxide in a molten carbonate. In addition, we discuss the molten carbonate fuel cell (MCFC) performance with a ternary system of (Li0.52Na0.48)2−2xAExCO3 (AE = Ca, Sr and Ba). Although the solubility of nickel oxide in the molten carbonate was reduced with an increase in the amount of additives, large amount of additives bring a low cell performance. We have made progress in the optimization of the carbonate composition through investigations as to durability by small-sized cell testing under a pressurized condition. The addition of SrCO3 was deemed inadequate by the failure of cell voltage within a 1000-h operating period. From the single cell operation results of periods up to 5000 h, we concluded that the addition of 9 mol% CaCO3 and 9 mol% BaCO3 to 52 mol% Li2CO3–Na2CO3 preserved the cell performance. This electrolyte composition is expected to yield an efficiently performing and durable MCFC.
The energy efficiency of alkaline water electrolysis improved by using the polyvinylidene fluoride-grafted 2-methacrylic acid 3-(bis-carboxymethylamino)-2-hydroxyl-propyl ester bipolar membrane (PVDF-g-G-I BM) as diaphragms with an ultrasonic field (USF) has been explored in this study. The PVDF-g-G-I BM was prepared by the plasma-induced polymerization method. The method utilized the porous PVDF membrane as substrates, and G-I monomer was grafted onto both sides of the PVDF membrane after plasma treatment. The performance of the PVDF-g-G-I BM was demonstrated by measuring the cell voltage for the cell operated with or without an USF. According to steady-state E–I curves, the order of the cell voltage for alkaline water electrolysis was the DuPont commercial membrane > Water > PVDF-g-G-I BM under the same working condition. The PVDF-g-G-I BM was found to function well as a diaphragm in alkaline water electrolysis. In comparison with Water without an USF, the H2 production efficiency by using the PVDF-g-G-I BM was improved 5–16/4% and an energy saving of ca. 15–20% (13–18%)/8–12% (6–10%) can be reached in alkaline water electrolysis at 0.5 M (1.0 M) NaOH for the cell operated with/without an USF, respectively.
The electrolyte substrate (matrix) of a molten carbonate fuel cell (MCFC) provides both ionic conduction and gas sealing. During the starting-up and operating of MCFC stacks at 923 K, the matrix can experience mechanical stresses that can cause cracking. In particular, the pure α-LiAlO2 that is generally used for the MCFC possesses poor mechanical strength. In this study, we employed Al and Li2CO3 particles as reinforcement materials to increase the mechanical strength of the α-LiAlO2 matrix for its stable long-term operation. The mechanical strength of the matrix increased dramatically after adding Al particles into the pure matrix. Moreover, we operated a single cell for 2000 h after adding Li2CO3 particles into the Al-reinforced matrix to prevent a Li-ion shortage caused by a lithiated Al reaction in the matrix.
The stability of La2Mo2O9−δ oxide-ion conductor was studied under Ar–H2 and controlled oxygen partial pressure (pO2) atmospheres within the range 608 ≤ T ≤ 1000 °C, by thermogravimetry (TG), X-ray Diffraction (XRD), Temperature Controlled X-ray Diffraction (TCXRD) and Scanning Electron Microscopy (SEM).At 608 °C under Ar–H2 flowing atmosphere, La2Mo2O9 phase was found to be unstable and reduction leads to an amorphous phase with composition close to La2Mo2O6.88. The stability of this amorphous phase under Ar–H2 was analyzed by TCXRD and found to be stable below 900 °C. Isothermal TG under controlled pO2 at 1000 °C indicated that La2Mo2O9−δ is not stable below 10−7 Pa and decomposition took place without the formation of La7Mo7O30 or amorphization.
The electrochemical performances of fuel cells using nano-ceria-salt composites electrolyte (NANOCOFC) have been investigated at different temperatures in molten carbonate fuel cell (MCFC) environment. The maximum output power density increased with the temperature, and reached 140 mW/cm2 at 650 °C. After operating for 200 h, the open circuit voltage (OCV) can keep the same value and the output power density only deceased 0.08%. It demonstrated that the NANOCOFC possessed the perfect stability of electrochemical performance in the MCFC environment. However, it was found that the output power density of the fuel cell in MCFC environment was much lower than that of fuel cell in SOFC environment. It was implied that the carbonate transfer would hinder the conduction of both proton and oxygen ion, which result in the poor output power density of fuel cells.
Ba1−xLaxSc1−yZryO3−δ with perovskite-related structure was synthesized by dopes of La and Zr to Ba-site and Sc-site of Ba2Sc2O5, respectively. The lattice parameters were refined by the Rietveld analysis with space group Pm3m. The total electrical conductivities of Ba1−xLaxSc1−yZryO3−δ measured by DC four-probe method were found to be about 10− 2 S·cm− 1 at 1000 °C in air and contributed by oxide ion, proton, and hole. The oxide ion transport number of Ba1−xLaxSc1−yZryO3−δ determined by ion blocking method increased with decreasing temperature.
The incorporation of praseodymium in the apatite-type lattice of La9.83−xPrxSi4.5Fe1.5O26±δ (x=0–6) decreases the unit cell volume, suppresses Fe4+ formation according to Mössbauer spectroscopy, and increases p- and n-type electronic contributions to total conductivity, studied by the impedance spectroscopy and modified faradaic efficiency (FE) and electromotive force (EMF) methods at 973–1223 K. The additions of praseodymia have no essential effect on the ionic transport, with an activation energy of 99–109 kJ/mol, under oxidizing conditions. Contrary to the Al-containing analogue, La9.83Si4.5Al1.5O26, exhibiting p(O2)-independent conductivity at oxygen pressures from 10−20 to 0.5 atm, the ionic conductivity of La9.83−xPrxSi4.5Fe1.5O26±δ decreases on reducing p(O2) below 10−14–10−12 atm. The observed behavior suggests a presence of hyperstoichiometric oxygen, critical for the level of ionic conduction and compensated by the formation of Fe4+ or Pr4+. The ion transference numbers in air vary in the range 0.979–0.994 for La9.83−xPrxSi4.5Fe1.5O26+δ, whilst for La9.83Si4.5Al1.5O26 the p-type electronic contribution to the total conductivity is lower than 0.5%. The average thermal expansion coefficients (TECs) of silicate-based solid electrolytes are (8.8–9.4)×10−6 K−1 at 300–1200 K and (14.2–15.8)×10−6 K−1 at 1200–1350 K.
The oxygen reduction reaction on smooth gold electrodes on Li/K (53: 47 at.%) carbonate melt has been examined in the temperature range 700–800°C. As in previous work on the Na/K melt [2], two chemically produced species (O22− O2−) are reduced in parallel steps. The waves for the reduction of these species are close together in this melt, as distinct from those in the Na/K eutectic [2]. Exchange currents are somewhat higher than in the Na/K melt. Again, neutralization of the O2− ion by CO2 in rather slow, and may be rate-determining in porous electrodes.
Early attempts to generate electrical energy electrochemically are briefly discussed. The author in 1932 chose the hydrogen-oxygen cell to work on, as this appeared to give most promise of practical results. The approach throughout was from an engineering point of view. The various stages through which the work passed are described, leading finally to the development and construction, in the United States, of a fully automatic power source that provides the auxiliary power for the command and service modules in the Apollo space project. A brief description is given of other types of hydrogen- oxygen cell, for example the ion-exchange membrane type used in the Gemini flights. Great efforts are now being made all over the world to adapt the fuel cell for use with conventional hydrocarbon fuels and air; the many difficulties that must be overcome before a unit suitable for ordinary commercial use can be achieved will be enumerated. The experience built up in the field of fuel cells is now being applied to the development of lightweight electrochemical storage systems, the need for which is becoming of paramount importance, especially for the propulsion of city traffic.
The degradation of cathode materials due to the so-called ‘NiO dissolution’ problem, is one of the most critical issues restricting the long-term operation of molten carbonate fuel cells (MCFCs). To overcome this problem, a modified NiO powder is prepared by the annealing of a pre-mixed powder consisting of Ni powder and Co3O4 nano-particles (n-Co3O4) at 650°C. Annealing above 300°C plays an important role in converting the physically bound mixed oxide system to a chemically bound system and, therefore, the separation of n-Co3O4 from Ni is prevented. This modification leads to the formation of a Ni0.9Co0.1O solid solution, and the lithiated Ni0.9Co0.1O has a core–shell structure that consists of different Li contents. Whereas the core phase has a low concentration of lithium, the outer layer is a highly lithiated phase. Since the highly lithiated outer phase, acting as a barrier, minimizes the dissolution of NiO, the modified cathode demonstrates good electrochemical properties and chemical stability under actual operating conditions. This study can provide an effective way to mass produce MCFC cathode materials.
The past 10 years have witnessed a tremendous acceleration in research devoted to non-fluorinated polymer membranes, both as competitive alternatives to commercial perfluorosulfonic acid membranes operating in the same temperature range and with the objective of extending the range of operation of polymer fuel cells toward those more generally occupied by phosphoric acid fuel cells. Important requirements are adequate membrane mechanical strength at levels of functionalization (generally sulfonation) and hydration allowing high proton conductivity, and stability in the aggressive environment of a working fuel cell, in particular thermohydrolytic and chemical stability. This review provides an overview of progress made in the development of proton-conducting hydrocarbon and heterocyclic-based polymers for proton exchange and direct methanol fuel cells and describes the various approaches made to polymer modification/synthesis and salient properties of the materials formed, including those relating to proton transport and proton conductivity, e.g., water diffusion and electro-osmotic drag. The microstructure, deduced from small angle X-ray and neutron diffraction measurements of representative non-fluorinated polymers is compared with that of perfluorosulfonic acid membranes. Different degradation mechanisms and aging processes that can result in chemical and morphological alteration are considered, and recent characterization of membrane-electrode assemblies (MEAs) in direct methanol and hydrogen-air (oxygen) fuel cells completes this review of the state of the art. While several types of non-fluorinated polymer membrane have demonstrated lifetimes of 500-4000 h, only a limited number of systems exist that hold promise for long-term operation above 100oC.1
The hybrid direct carbonfuelcell (HDCFC) with solid oxide and molten carbonate binary electrolyte merges solid oxidefuelcell (SOFC) and molten carbonatefuelcell technologies to achieve direct conversion of solid carbon to electric power. The purpose of this study is to investigate in detail the electrochemistry of the oxidation of solid carbon in the carbon/carbonate slurry in the HDCFC. A planar test cell has been fabricated employing conventional SOFC materials and a eutectic carbonate mixture of lithium carbonate and potassium carbonate. The HDCFC with a model fuel, carbon black XC-72R, shows very high open circuit voltages (OCVs), approximately 1.5 V at 550–700 °C, especially after a high temperature operation at 900 °C, where carbonate decomposes to O2− and CO2. The carbon/carbonate slurry increases the active reaction zone from a two-dimensional Ni/YSZ anode to a three-dimensional slurry and significantly enhances the carbonoxidation. The high OCV is probably due to the low activity of CO2 in the slurry, which results from the recombination of CO2 and O2−. Gaseous products were analysed using an online gas chromatograph, and CO2 and CO were detected, with their selectivity found to be dependent on temperature. Solid carbon is electrochemically oxidised to CO2 and the final distribution of the products is dominated by the equilibrium of the Boudouard reaction (C + CO2 2CO).
Poly(arylene ether sulfone)s have been functionalised with alkyl side chains carrying phosphonic acid and bis(phosphonic acid) in order to investigate their properties as membrane materials. The phosphonated and bisphosphonated polymers were synthesised via lithiation of poly(arylene ether sulfone)s, followed by reactions with triethyl 3-phosphonopropionate and tetraisopropyl vinylidenediphosphonate, respectively. Flexible and mechanically tough acidic membranes were cast from solution after hydrolysis of the estergroups. The significantly higher acidity and acid concentrations of the membranes containing the tetraprotic bis(phosphonic acid) led to higher conductivities in comparison to the membranes containing the diprotic phosphonic acid. Membranes containing 1.7 mmol of bis(phosphonic acid)/g dry polymer absorbed 28 wt% water when immersed at room temperature, and a conductivity of 25 mS/cm was measured at 120 °C. Moreover, the bisphosphonated membranes did not decompose at temperatures of up to 240 °C under air. The study also showed that high degrees of hydrolysis of the bisphosphonate units were crucial in order to reach the high proton conductivity and thermal stability necessary for fuelcell applications.
The substitutional range and cell parameter evolution of fast oxide-ion conductors La2−xRxMo2−yWyO9
(R = Nd, Gd) are investigated. In the whole series, the cubic β-La2Mo2O9 structural type is stabilized at room temperature. The effects on reducibility of both single and double substitutions are presented. Lanthanum substitution by rare earth appeared to be responsible for an increase in the reducibility and a strong but reversible amorphization under dilute hydrogen. On the contrary, the favourable role of tungsten on the compound stability under reducing conditions is evidenced: it depletes oxygen loss while making the La2Mo2O9 structural type less affected by it.
Al can be doped into the oxide ion conductor La9.33(SiO4)6O2 according to the formula La9.33 + x/3(SiO4)6 − x(AlO4)xO2 where 0 ≤ x ≤ 2; a conductivity enhancement of 1–2 orders of magnitude is observed for intermediate x values and illustrates the important role that La vacancies have in optimising the conductivity.
Lithiated NiO cathode dissolution has been a major problem for the development of molten carbonate fuel cells (MCFCs). Many studies have been contributed to find new alternative cathodes; here, lithium cobalt oxide, LiCoO2, was coated onto the commonly used NiO cathode by the electroplating method and the resulting cathode showed much reduced solubility compared with that of the common nickel oxide cathode. Thin film lithium cobalt oxide was prepared by the oxidation of Co metal deposited on a nickel plate in molten (Li,K)2CO3 at 650°C under a CO2–O2
(2 ∶ 1 vol%) atmosphere. When this coated nickel plate was oxidized, the open circuit potential (OCP) decayed gradually, indicating two well-defined potential plateaux; the oxide films produced at each potential plateau were identified by X-ray diffraction methods. The surface product at the first plateau was CoO. LiCoO2 was formed at the second OCP plateau [around −0.47 V vs. CO2–O2
(2 ∶ 1 vol%) reference electrode]. By the same method, LiCoO2 was coated onto a porous nickel cathode in order to produce a MCFC.
A new family of fast O2− conductors, which exhibit
anionic conductivity comparable to that of stabilised zirconia, is presented.
The parent compound of this new family, hereafter called LAMOX, is lanthanum
molybdate La2Mo2O9. Various substitutions
have been attempted: on the lanthanum site (La2 − xAx)Mo2O9 with A = Sr, Ba, K, or Bi; on the molybdenum site La2(Mo2 − xBx)O9 with B = Re, S, W, Cr
and V; and on the oxygen site with fluorine. Most of these substitutions suppress
the phase transition which occurs in La2Mo2O9
around 580°C from a low temperature α form to a high temperature (more
conducting)
β form, and stabilise the β form at room temperature.
Several members of the LAMOX series are studied through X-ray and neutron
diffraction, and conductivity measurements. Large O2− thermal
factors and local static disorder agree well with the anionic nature of the
conductivity. Partly vacant sites with short inter-site distances suggest
a most probable conduction path with tridimensional character.
Ionic conductivities have been investigated for lanthanoid silicates of the Ln10(SiO4)6O3 solid solution series and related compounds. The activation energy and conductivity at 500 °C were estimated to be 69 kJ mol–1 and 1.8 × 10–4 S cm–1 for La10(SiO4)6O3 and 71 kJ mol–1 and 1.5 × 10–4 S cm–1 for Nd10(SiO4)6O3. The a and c lattice constants of the hexagonal phase decreased with decreasing radius of the Ln3+ ion for Ln10(SiO4)6O3(Ln = La, Nd, Sm, Gd and Dy). The activation energy increased and the conductivity decreased when Ln3+ ions with smaller ionic radii were used. The sole carrier in these materials is the O2– ion.
The crystal structure of the new fast oxide-ion conductor La2Mo2O9 (ionic conductivity of 0.06 S cm-1 at 800 °C) has been studied. This compound presents a reversible phase transformation around 580 °C from a low-temperature form α-La2Mo2O9 to a high-temperature form β-La2Mo2O9. The high-temperature form β-La2Mo2O9 has a cubic structure (at 617 °C, space group P213; a = 7.2014(5) Å; Z = 2; RBragg = 5.8%, Rp = 10.9%, Rwp = 6.5%, χ2 = 7.7) which derives from that of β-SnWO4. Partial site occupation by oxygen atoms, strongly anisotropic thermal factors, and short-range order with a distance characteristic of O−O pairs have been evidenced. An original concept is proposed for the origin of oxide−ion conduction in this compound, which could be applied to the design of new oxide−ion conductors. The low-temperature form α-La2Mo2O9 exhibits a slight monoclinic distortion and a large superstructure relative to β-La2Mo2O9 (2 × 3 × 4), most probably due to the localization of oxygen atoms. The large cell (8800 Å3) did not allow us to determine the crystal structure of α-La2Mo2O9.
The particular properties of molten carbonates, oxyanionic salts, allow their application in the promising technological field of fuel cells. A general description of this class of molten salts is presented, outlining the importance of the oxoacidity concept and potential-acidity diagrams to understand the main features of this electrochemical device, dedicated to energy and heat generation. The main characteristics of the molten carbonate fuel cell (MCFC) are reviewed from the single cell, including the matrix electrolyte and the electrode mechanisms, to the stack, with a special attention to the bipolar plates. The factors limiting MCFC lifetime are discussed in order to analyze the potential improvements of the materials presently used. An overview of the principal demonstration prototypes all over the world is given. Finally, some conditions for the introduction of MCFC in the commercial energy market are briefly mentioned.
Single crystal of hexagonal apatite type Nd9·33(SiO4)6O2 which is an oxide ionic conductor was prepared by the FZ method and an anisotropy of its conductivity was investigated. The conductivity of a parallel component to a c-axis (2·1×10−8 Scm−1 at 30°C) was higher about one order of magnitude, compared with that of perpendicular component.
Protonic ceramic membrane fuel cells (PCMFCs) based on proton-conducting electrolytes have attracted much attention because of many advantages, such as low activation energy and high energy efficiency. A stable, easily sintered perovskite oxide BaCe0.5Zr0.3Y0.16Zn0.04O3−δ (BCZYZ) as electrolyte for proton-conducting solid oxide fuel cells (SOFCs) with Sm0.5Sr0.5CoO3−δ (SSC) composite cathode is investigated. By fabricating thin membrane BCZYZ electrolyte (∼20μm) synthesized by a modified Pechini method on NiO–BCZYZ anode support, PCMFCs are assembled and tested by selecting SSC perovskite cathode with high mixed ionic and electronic conductivities. An open-circuit potential of 1.015V, a maximal power density of 528mWcm−2, and a low polarization resistance of the electrodes of 0.15Ωcm2 is achieved at 700°C. The results indicate that BCZYZ proton-conducting electrolyte with SSC cathode is a promising material system for SOFCs.
A research and development program is under way at the Idaho National Laboratory (INL) to assess the technological and scale-up issues associated with the implementation of solid-oxide electrolysis cell technology for efficient high-temperature hydrogen production from steam. This work is supported by the US Department of Energy, Office of Nuclear Energy, under the Nuclear Hydrogen Initiative. This paper will provide an overview of large-scale system modeling results and economic analyses that have been completed to date. System analysis results have been obtained using the commercial code UniSim, augmented with a custom high-temperature electrolyzer module. Economic analysis results were based on the DOE H2A analysis methodology. The process flow diagrams for the system simulations include an advanced nuclear reactor as a source of high-temperature process heat, a power cycle and a coupled steam electrolysis loop. Several reactor types and power cycles have been considered, over a range of reactor outlet temperatures. Pure steam electrolysis for hydrogen production as well as coelectrolysis for syngas production from steam/carbon dioxide mixtures have both been considered. In addition, the feasibility of coupling the high-temperature electrolysis process to biomass and coal-based synthetic fuels production has been considered. These simulations demonstrate that the addition of supplementary nuclear hydrogen to synthetic fuels production from any carbon source minimizes emissions of carbon dioxide during the production process.
Very thin diaphragms (0.2 mm) having high mechanical and chemical stability, against corrosion and dissolution in 40 wt% KOH at temperatures up to 160°C, were developed to exhibit low surface resistances (0.2 ωcm2) and high gas-separation properties. These diaphragms are made of a highly porous cermet made of nickel and oxide ceramic particles which is supported by a woven nickel-net. The corrosion of the metal-screen is safely prevented during electrolyzer operation by a steady flow of H2-saturated electrolyte across the diaphragm. The stability of the oxide ceramics is obtained from thermodynamic stability and low solubility in caustic potash. It is possible to produce integrated electrode-diaphragm sandwiches from these diaphragms by applying high porous nickel-layers on their faces by relatively simple sinter-techniques.
An R & D programme based on the development and parametric testing of water electrolysis cells for hydrogen production has been directed towards the development of electrolytic systems based on the use of inorganic ion exchange membranes.Attention was focused on the use of polyantimonic acid-teflon bound membranes which can be produced in thin sheets of 250 μm thickness. By attaching on both sides of the membrane catalytically active electrodes an electrolysis unit cell is obtained.At 10 kAm−2 and 85 C, cell voltages of 1.8 V have been measured in a reproducible way using these heterogeneous inorganic ion exchange membranes.A technological demonstration set-up has been initiated involving the construction of a 1 kW filter press type electrolyzer.
A composite of samarium doped ceria (SDC) and a binary carbonate eutectic (52mol% Li2CO3/48mol% Na2CO3) is investigated with respect to its morphology, conductivity and fuel cell performances. The morphology study shows the composition could prevent SDC particles from agglomeration. The conductivity is measured under air, argon and hydrogen, respectively. A sharp increase in conductivity occurs under all the atmospheres, which relates to the superionic phase transition in the interface phases between SDC and carbonates. Single cells with the composite electrolyte are fabricated by a uniaxial die-press method using NiO/electrolyte as anode and lithiated NiO/electrolyte as cathode. The cell shows a maximum power density of 590mWcm−2 at 600°C, using hydrogen as the fuel and air as the oxidant. Unlike that of cells based on pure oxygen ionic conductor or pure protonic conductor, the open circuit voltage of the SDC–carbonate based fuel cell decreases with an increase in water content of either anodic or cathodic inlet gas, indicating the electrolyte is a co-ionic (H+/O2−) conductor. The results also exhibit that oxygen ionic conductivity contributes to the major part of the whole conductivity under fuel cell circumstances.