Rechargeable metal–air batteries and water splitting are highly competitive options for a sustainable energy future, but their commercialization is hindered by the absence of cost-effective, highly efficient and stable catalysts for the oxygen evolution reaction. Here we report the rational design and synthesis of a double perovskite PrBa0.5Sr0.5Co1.5Fe0.5O5+δ nanofiber as a highly efficient and robust catalyst for the oxygen evolution reaction. Co-doping of strontium and iron into PrBaCo2O5+δ is found to be very effective in enhancing intrinsic activity (normalized by the geometrical surface area, ∼4.7 times), as validated by electrochemical measurements and first-principles calculations. Further, the nanofiber morphology enhances its mass activity remarkably (by ∼20 times) as the diameter is reduced to ∼20 nm, attributed to the increased surface area and an unexpected intrinsic activity enhancement due possibly to a favourable eg electron filling associated with partial surface reduction, as unravelled from chemical titration and electron energy-loss spectroscopy. The design of efficient and stable oxygen evolution catalysts has implications for water splitting and metal-air battery technology. Here, the authors fabricate double perovskite nanofibers and demonstrate the favourable effects of co-doping and nanostructuring on oxygen evolution performance.

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A tailored double perovskite nanofiber catalyst enables ultrafast oxygen evolution

Cobalt based layered perovskites as cathode material for intermediate temperature Solid Oxide Fuel Cells: A brief review

This review paper focuses on the phenomenon of thermochemical expansion of two specific categories of conducting ceramics: Proton Conducting Ceramics (PCC) and Mixed Ionic-Electronic Conductors (MIEC) The theory of thermal expansion of ceramics is underlined from microscopic to macroscopic points of view while the chemical expansion is explained based on crystallography and defect chemistry Modelling methods are used to predict the thermochemical expansion of PCCs and MIECs with two examples: hydration of barium zirconate (BaZr1−xYxO3−δ) and oxidation/reduction of La1−xSrxCo02Fe08O3−δ While it is unusual for a review paper, we conducted experiments to evaluate the influence of the heating rate in determining expansion coefficients experimentally This was motivated by the discrepancy of some values in literature The conclusions are that the heating rate has little to no effect on the obtained values Models for the expansion coefficients of a composite material are presented and include the effect of porosity A set of data comprising thermal and chemical expansion coefficients has been gathered from the literature and presented here divided into two groups: protonic electrolytes and mixed ionic-electronic conductors Finally, the methods of mitigation of the thermal mismatch problem are discussed

https://www.mdpi.com/2073-4352/8/9/365/pdf

Thermal and Chemical Expansion in Proton Ceramic Electrolytes and Compatible Electrodes

Bismuth has been doped into mixed ionic–electronic conducting La1.75Sr0.25NiO4+δ (LSN) with the 2D K2NiF4-type structure to evaluate its influence on various properties of the host material, which include its potential use as a SOFC cathode. X-ray powder diffraction indicates that LSN retains its tetragonal structure after doping with 5 mol% bismuth to form La1.65Bi0.1Sr0.25NiO4+δ (LSN–Bi). Bismuth doping profoundly lowers (by ∼150 °C) the sintering temperature of LSN. Both LSN and LSN–Bi show excellent compatibility with electrolytes yttria-stabilized zirconia (YSZ) and samaria-doped ceria (SDC) in terms of thermal expansion and chemical reactivity (<900 °C). The electrical conductivity of both materials is metallic like and reaches values of 99.3 S cm−1 and 100.3 S cm−1 at 550 °C for LSN and LSN–Bi, respectively. The data from electrical conductivity relaxation (ECR) measurements demonstrate that the substitution of lanthanum by bismuth enhances the chemical diffusion coefficient (Dchem) and surface exchange coefficient (kchem) by factors of 2–3. The faster kinetics of oxygen transport exhibited by LSN–Bi relative to parent LSN is reflected by a lower polarization resistance of the former when the electrode performance of both materials is compared in symmetric cells. The corresponding values at 700 °C are 4.2 Ω cm2 and 0.61 Ω cm2 for LSN and LSN–Bi, respectively. High peak power densities are achieved (328 mW cm−2 and 131 mW cm−2 at 700 and 600 °C, respectively), when LSN–Bi is incorporated as the cathode in a fuel cell operated with humidified hydrogen as the fuel and air as the cathode gas. The material is considered a promising candidate for further study.

Dongsheng Yin

Papers

Synthesis and characterization of PrBa0.5Sr0.5Co2−xNixO5+δ (x=0.1, 0.2 and 0.3) cathodes for intermediate temperature SOFCs