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The commercialization of solid oxide fuel cells (SOFCs) can be significantly promoted with the direct utilization of methane, which is the primary component in natural gas and the second most abundant anthropogenic greenhouse gas. However, carbon deposition on most commonly used Ni-based anode is the bottle-necking issue inhibiting long-term stability of direct methane SOFCs. To avoid such a problem, methane is typically reformed (internally or externally) in SOFCs. Considering the cost, system simplification, coking resistance, and material selection, the on-cell catalytic reforming layer (OCRL) is one of the most promising designs for direct methane SOFCs. Reforming catalytic materials are typically consisted of active component, substrate and catalytic promoter, all of which have a significant impact on the catalytic activity, sintering resistance and coking resistance of methane reforming catalysts. This review summarizes the influence of the various components, some common OCRL materials and their applications in direct methane SOFCs, reforming and coking resistance mechanism, as well as the remaining challenges. The effective utilization of OCRL plays a pivotal role in promoting the development of direct methane SOFCs and the commercialization of SOFCs. • Recent progress of on-cell catalytic reforming layer for SOFC is presented. • Influence of composition on the properties of the reforming catalyst is summarized. • Challenges and prospects of on-cell catalytic reforming layer in SOFCs are provided. [ABSTRACT FROM AUTHOR]

It is well known that conventional solid oxide fuel cells (SOFCs) based on oxide ion conducting electrolyte (e.g., yttria-stabilized zirconia, YSZ) and nickel (Ni) - ceramic cermet anodes are susceptible to poisoning by trace amount of hydrogen sulfide (H 2 S) while not significantly impacted by the presence of carbon dioxide (CO 2 ) and moisture (H 2 O) in the fuel stream unless under extreme operating conditions. In comparison, the impacts of H 2 S, CO 2 , and H 2 O on proton-conducting SOFCs remain largely unexplored. This study aims at revealing the poisoning behaviors caused by H 2 S, CO 2 , and H 2 O for proton-conducting SOFCs. Anode-supported proton-conducting SOFCs with BaZe 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3 (BZCYYb) electrolyte and Ni-BZCYYb anode and La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) cathode as well as Ni-BZCYYb/BZCYYb/Ni-BZCYYb anode symmetrical cells were subjected to low ppm-level H 2 S or low percentage-level CO 2 or H 2 O in the hydrogen fuel, and the responses in cell electrochemical behaviors were recorded. The results suggest that, contrary to conventional SOFCs that show sulfur poisoning and CO 2 and H 2 O tolerance, such proton-conducting SOFCs with Ni-BZCYYb cermet anode seem to be poisoned by all three types of "contaminants". Beyond that, the implications of the experimental observations on understanding the fundamental mechanism of anode hydrogen electrochemical oxidation reaction in proton conducting SOFCs are also discussed. [ABSTRACT FROM AUTHOR]

Proton conducting intermediate temperature (400-700°C) solid oxide fuel cells (IT-SOFC) have attracted great interest recently. However, for SOFC operation at intermediate temperature, cathode is often considered to be the main factor limiting the overall cell performance. In this study, Ba0.5Sr0.5Co0.8Fe0.2O3-δ (BSCF), which is one of the most active cathode materials and shows significant hydration effect suggesting possible proton conductivity, was investigated as the cathode for proton conducting IT-SOFC at temperature down to ∼450°C. The stability and compatibility of BSCF cathode with BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb), one of the leading proton conducting electrolyte materials, were studied at intermediate temperature in various atmospheres. In addition, experiments were carried out to understand the electrochemical behaviors of BSCF as a mixed proton, oxide ion and electron conducting cathode using BSCF/BZCYYb/BSCF symmetrical cells in simulated air containing different concentrations of water vapor (H2O) and carbon dioxide (CO2), especially at lower temperature of ∼450°C. The results are analyzed from the underlying oxygen electrode reaction mechanism point of view, and the direction for future research to further improve the cathode for proton conducting IT-SOFC is pointed out. [ABSTRACT FROM AUTHOR]

• The origin, structure, and properties of Sr 2 Fe 1.5 Mo 0.5 O 6 were presented. • The optimization and application of Sr 2 Fe 1.5 Mo 0.5 O 6 -based oxides for SOCs were summarized. • Some challenges and prospects of Sr 2 Fe 1.5 Mo 0.5 O 6 -based oxides were put forward. The development of solid oxide electrochemical cells (SOCs) coincides with the policy of emission peak and carbon neutrality, and possesses significant commercial prospects in the future energy market. Developing perovskite oxides with mixed oxygen ionic and electronic conductivity is an effective approach to alleviate the issues caused by lowering the operating temperature and the utilization of hydrocarbon fuel. Recently, Sr 2 Fe 1.5 Mo 0.5 O 6-δ with double perovskite structure exhibits high conductivity, excellent redox stability and catalytic activity in both air and hydrogen environments, and presents broad application prospects in SOCs. Surface modification and element doping further enhance the electro-catalytic activity of the Sr 2 Fe 1.5 Mo 0.5 O 6-δ electrode, enabling a broader application prospect in SOCs. This review summarizes the structures, properties, applications, shortcomings, and optimizations of the Sr 2 Fe 1.5 Mo 0.5 O 6-δ -based oxides in detail. The research and development of the Sr 2 Fe 1.5 Mo 0.5 O 6-δ -based oxides have specific guidance and assistance for the progress of intermediate temperature SOCs. [ABSTRACT FROM AUTHOR]

Coking is a major issue with the traditional Ni-based anodes when directly oxidizing CH 4 in solid oxide fuel cells (SOFCs). Dry reforming to convert CH 4 –CO 2 into CO–H 2 syngas before entering Ni-based anode may potentially be an effective and economical method to address the coking problem. Consequently, an on-cell reforming layer outside the Ni-based anode is expected to offer a unique solution for direct CH 4 –CO 2 SOFCs without coking. In this study, Ni-GDC anode-supported cells with and without a Sr 2 Co 0.4 Fe 1.2 Mo 0.4 O 6-δ (SCFM) layer outside the anode support have been fabricated and evaluated using either H 2 or CH 4 –CO 2 as fuel. Both types of cells show excellent electrochemical performance when H 2 is used as fuel, and the SCFM layer has negligible impact on the cell performance. When CH 4 –CO 2 is used as fuel, however, the electrochemical performance and durability of the cells with the SCFM layer are much better than those without the SCFM layer outside the Ni-GDC anode, indicating that the SCFM layer can efficiently perform dry reforming. This unique on-cell dry reforming design enables direct CH 4 –CO 2 solid oxide fuel cells and offers a very promising route for energy storage and conversion. • Sr 2 Co 0.4 Fe 1.2 Mo 0.4 O 6-δ catalytic reforming layer was added outside the anode support. • The reforming layer showed negligible effect on the cell performance fed with H 2. • Cell performance and durability are improved with reforming layer when fed with CH 4 –CO 2. [ABSTRACT FROM AUTHOR]

Lowing the operating temperature can greatly promote the commercialization of solid oxide fuel cells (SOFCs), however it also results in a significant increase in cell impedance, which is the bottleneck for the development of intermediate temperature SOFCs (IT-SOFCs). Major hurdles in developing conventional single-phase cathode materials for IT-SOFCs are poor electrochemical performance or durability. The investigation of new cathode materials or the optimization of the existing cathodes is imminent for the development of IT-SOFCs. Among them, core-shell structured cathode can combine the advantages of multiple components, and has been demonstrated with excellent oxygen reduction reaction (ORR) catalytic activity and long-term stability. This review summarizes the recent research progress on core-shell structured cathode for enhanced electrochemical performance, long-term stability, CO 2 tolerance and Cr tolerance. Furthermore, the future directions are discussed from a perspective of materials design, preparation and characterization. Core-shell structured cathodes are expected to play an increasingly critical role in the commercialization of IT-SOFCs. • The recent development of core-shell structured cathode were presented. • The CO 2 -tolerance and Cr-tolerance effects were summarized firstly. • Propose some outlooks for characterization, optimization and materials selection. [ABSTRACT FROM AUTHOR]