Highly active hydrogen evolution catalysis on oxygen-deficient double-perovskite oxide PrBaCo2O6-delta

Efficient hydrogen evolution on water splitting is a crucial issue to achieve a sustainable society based on renewable energy. Highly active and cost-effective catalysts for oxygen/hydrogen evolution reactions (OERs/HERs) are desired to suppress the intrinsically significant overpotential of these reactions. Perovskite-related transition-metal oxides have been widely investigated as promising candidates for electrochemical catalysts, whereas their complex composition and structure inhibit the elucidation of essential factors for activating HER. Herein, we report a systematic study on predominant factors affecting HER catalysis for Co-containing perovskite-related oxides. The A-site-ordered double perovskite oxide PrBaCo2O6-delta exhibits HER activity with a volcano-type plot associated with oxygen deficiency content, and shows the highest activity at a moderate value of delta = 0.2, in addition to the significant superiority to the simple ABO(3)-type perovskite, ACoO(3) (A = La, La0.5Ca0.5, Ca). Based on the Tafel slope, electric conductivity, and charge-transfer resistance analyses, we have found that complementary factors dominate the HER catalysis; Co-O covalency and water dissociation site, which are respectively induced by high Co valence and oxygen deficiency. This finding provides new insight into the rational design of transition-metal oxide catalysts for HER.