Some aspects of hydrogen oxidation in solid oxide fuel cell: A brief historical overview

Environmentally friendly and resource-efficient ways to generate, convert, store and transport electricity are important areas of scientific and technological development. Fuel cells are direct converters of chemical energy into electricity with low emissions of harmful components. One of the most promising types of fuel cells is the solid oxide fuel cell (SOFC). The electrical power generated by the SOFC is mainly limited by the ohmic resistance of the electrolyte and the polarization of the electrodes. The ohmic resistance can be reduced by reducing the thickness of the electrolyte. To reduce the polarization resistance, other approaches are needed, namely a detailed study of the mechanisms of electrode reactions and the determination of the nature of rate-determining stages. Until now, fuel oxidation at the anode of the SOFC, as opposed to oxygen reduction at the cathode, has not been well understood. Even for conventional nickel-ceramic anodes, there is no clear understanding of the nature of the rate-determining steps of hydrogen oxidation. This review provides a brief historical background on the development of SOFCs, some insights into the oxygen reduction mechanisms, and a more detailed review of the kinetics of hydrogen oxidation at SOFC anodes.https://doi.org/10.15826/elmattech.2023.2.01

Structural stability and features of electrical and electrochemical behavior under reducing conditions of Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ material for the symmetrical SOFCs

In this study, a performance of the complex oxide composition of Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ was investigated from the viewpoint of its use as a fuel or symmetrical electrode for the electrochemical devices with a LaGaO3-based solid electrolyte. The results show that the above-mentioned oxide can be obtained as a single-phase composition using solid-phase synthesis with a final annealing temperature of 1150 °C. It has been shown that the oxide retains satisfactory stability at 800 °C in an atmosphere of 5 % H2 + Ar, only a minor amount, presumably of Co-Fe alloy, has been detected. The electrical conductivity of the oxide in wet hydrogen exhibits a linear semiconductor-type behavior with a conductivity value of 7 S · cm–1 at 800 °C. The polarization resistance of the Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ electrode in wet hydrogen atmosphere reaches approximately 1.09 Ω · cm2 at 800 °C, which is a relatively high value for the electrodes of electrochemical devices. A significant reduction in resistance down to 0.43 Ω · cm2 is observed for the electrode activated with impregnated ceria. It has been demonstrated that the observed decrease in resistance is due to the expansion of the area of the electrochemical reaction without changing its mechanism. The long-term tests with a duration of about 220 h at 800 °C in a wet hydrogen atmosphere demonstrate satisfactory stability of the electrochemical activity of the Pr0.4Sr0.6Co0.2Fe0.7Nb0.1O3–δ electrode, which can be considered as a promising electrode for intermediate temperature electrochemical devices, including those of symmetrical design.https://doi.org/10.15826/elmattech.2024.3.03

Recent advances in heteroatom substitution Sr2Fe1.5Mo0.5O6–δ oxide as a more promising electrode material for symmetrical solid-state electrochemical devices: A review

In recent years, the interest in solid state electrochemical devices has significantly increased due to the various cases of their use in the energy field. The first case is the solid oxide fuel cells with both oxygen-ion and proton-conducting membranes. The second case is the electrolysis cells for hydrogen production. As a rule, in both cases, electrochemical cells consist of an ion-conducting membrane and two different electrodes. The present review is focused on structural, physicochemical, and electrochemical properties of a complex oxide based on strontium ferrite with partial replacement of iron by molybdenum. This complex oxide has a number of unique characteristics: in particular, it is able to function effectively as an electrode in oxidizing and strongly reducing atmospheres, which makes it a promising material for electrochemical devices based on solid electrolytes with symmetrical electrodes. Doping with elements in A-, B- and O-sublattices and surface modification increases electro-catalytic activity of Sr2Fe1.5Mo0.5O6−δ porous oxide material, which increases competitiveness of the electrode material for application in solid oxide electrochemical devices. Mechanisms for improving electro-catalytic activity are outlined stepwise by doping of different sublattices of double perovskite, by level of doping, and by different types of dopants. In conclusion, the data on material conductivity, power densities of both symmetric and fuel cells are systematized, and the remaining problems and prospects for future developments and upgrades of Sr2Fe1.5Mo0.5O6−δ oxide electrode material are described. keywords: Sr2Fe1.5Mo0.5O6−δ, IT-SOFCs, anode materials, cation doping, conductivity, anion doping, polarization resistance, symmetrical electrode DOI: https://doi.org/10.15726/elmattech.2022.1.00

Introductory editorial for Electrochemical Materials and Technologies

DOI: https://doi.org/10.15726/elmattech.2022.1.00

Structural and electrical properties of Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors with the pyrochlore structure

This work studies a series of synthesized Bi$_{1.6}$Mg$_{0.8-x}$Cu$_x$Nb$_{1.6}$O$_{7-\delta}$ ($x$ = 0.2, 0.4) semiconductors and their Lidoped compositions. A detailed structure investigation combining high-resolution neutron-, synchrotron-, and X-ray diffraction methods, as well as DFT calculations, revealed the preferential location of Cu and Li atoms at the Bi sites and Mg atoms at the Nb ones. According to high-temperature X-ray diffraction data, a structural modification caused by the activation of oxygen transport occurs at 200°C. The linear thermal expansion coefficient was found to be 3.6–4.6⋅10$^{−6}$ K$^{−1}$ (50–400°C). Magnetic susceptibility measurements allowed us to determine weak antiferromagnetic exchange interactions. The direct band gap was predicted using the DFTHSE03 hybrid functional calculation, and the optical direct band gap was estimated at 2.3–2.4 eV. Impedance spectroscopy and a dc four-probe technique were also employed to examine the samples$^,$ electrical properties. The high mixed electronic-ionic conductivity of the pyrochlores was detected, while the vacancies created by Lidoping in Bi$_{1.5-y}$Li$_y$Mg$_{0,375}$Cu$_{0,375}$Nb$_{1.5}$O$_{7-\delta}$ have been found not to affect the conductivity. Besides, the pyrochlores are chemically compatible with the La$_{0.7}$Sr$_{0.3}$MnO$_3$ perovskite (up to 800°C). These make us believe that the studied Mg–Cu- and Mg–Cu–Li-doped bismuth niobate semiconductors can become the basis for composite electrodes to boost their oxygen conductivity

Design of materials for solid oxide fuel cells, permselective membranes, and catalysts for biofuel transformation into syngas and hydrogen based on fundamental studies of their real structure, transport properties, and surface reactivity

Advances in design of materials for solid oxide fuel cells, oxygen and hydrogen separation membranes, and catalysts for biofuel conversion into syngas and hydrogen are reviewed. Application of new efficient techniques of material synthesis and characterization of their atomic-scale structure, transport properties, and reactivity allowed to develop new types of efficient cathodes and anodes for solid oxide fuel cells, asymmetric supported oxygen, and hydrogen separation membranes with high permeability and structured catalysts with nanocompositeactive components demonstrating high performance and stability to coking in steam/autothermal reforming of biofuels.FCTpublishe