(187b) Biphasic and High Entropy Oxide Electrocatalysts for Enhanced Performance in Acid for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) occurs in a wide range of electrochemical devices crucial for the conversion and storage of renewable energy sources. However, electrocatalysts commonly used for OER in acidic media are typically limited to Ir and its oxide, and other compounds often suffer from poor activity and stability. To address these challenges, this research presents a defect engineering approach to design new classes of solid-state structure by controlling multiple cation incorporation. We designed Y- and Ru-based biphasic oxides which exhibited better activity and stability than its single-phase parent compounds. Variations in ionic radii of the elements introduce lattice strain, while diverse oxidation states add complexity to the charge distribution within the material. TEM micrograph reveals that the oxide is enriched with phase boundaries. The interface between these phases can serve as active sites for catalytic reactions, enhancing overall catalytic performance. This is further confirmed by electrochemical surface area analysis which is higher for biphasic oxide (29.08 mFcm^-2). In addition, we further explored high entropy oxides (HEOs) electrocatalysts. HEOs reduce free energy by increasing configuration entropy (S_config) to make the oxide stable, thus enhancing stability for OER electrocatalysis. We chose cations of similar oxidation state (3⁺) and ionic radius to incorporate at the same crystal site (e.g., A site of pyrochlore) to avoid phase separation at low temperature. We designed (YLns)₂Ru₂O₇(Lns are lanthanide elements) high entropy pyrochlore oxide(S_config =1.71R) which is entropically stable. Our HEO catalyst shows better OER activity than single metal oxide as well as enhanced stability of 1000 h at 10 mA/cm² in three electrode system. We further tested the catalysts in membrane electrode assembly (MEA)-based water electrolyzer, showing promising results. This superior activity and stability showcase promising potential to utilize defect engineering as an efficient method for electrocatalyst design for PEM electrolyzer.