Novel OER/ORR Electrocatalysts Based on High-Entropy Perovskites with 3d/4d/5d Dopants

In this study, the feasibility of a new group of alkali-free high-entropy ABO3-δ perovskite cathodes, in which the B-site is occupied by a mixture of 3d and 4d/5d elements, is examined. Six different materials with a general formula of La(Cu0.2Ni0.2X10.2X20.2Y10.2)O3-δ (where X1, X2 = mixture of two Co, Ga, Fe, and Y1 = one of Nb/Ta): La(Cu0.2Ni0.2Co0.2Ga0.2Nb0.2)O3-δ, La(Cu0.2Ni0.2Co0.2Ga0.2Ta0.2)O3-δ, La(Cu0.2Ni0.2Fe0.2Ga0.2-Nb0.2)O3-δ, La(Cu0.2Ni0.2Fe0.2Ga0.2-Ta0.2)O3-δ, La(Cu0.2Ni0.2Co0.2Fe0.2Nb0.2)O3-δ, La(Cu0.2Ni0.2Co0.2Fe0.2Ta0.2)O3-δ were synthesized, with five of them possessing a single-phase, Pnma perovskite structure. While in the case of the basic properties, such as electrical conductivity or thermomechanical behavior, the studied oxides show a number of similarities, the differences between them become more apparent when low-temperature Oxygen Evolution Reaction (OER) and high-temperature Oxygen Reduction Reaction performance is evaluated. The overall best performance is achieved by La(Cu0.2Ni0.2Co0.2Fe0.2Nb0.2)O3-δ and La(Cu0.2Ni0.2Co0.2Fe0.2Ta0.2)O3-δ compositions, with the former offering slightly faster OER kinetics, and the latter exhibiting superior polarization resistance as an SOFC cathode. Overall, the materials exhibit a strong correlation between composition and properties, with potential for further development into non-equimolar compositions of superior performance.