Synergistic Effect between Fe&lt;sup&gt;4+&lt;/sup&gt; and Co&lt;sup&gt;4+&lt;/sup&gt; on Oxygen Evolution Reaction Catalysis for CaFe&lt;sub&gt;1−&lt;/sub&gt;&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;Co&lt;i&gt;&lt;sub&gt;x&lt;/sub&gt;&lt;/i&gt;O&lt;sub&gt;3&lt;/sub&gt;

Ikuya Yamada,Amane Morimura,Asuka Ochi,Seiji Oda,Wencong Wang,Kaoru Toda,Masaya Oshita,Yuta Kato,Yuta Kizawa,Atsushi Tanaka,Hajime Yamamoto,Hidekazu Ikeno,Shunsuke Yagi,Manami Goto,Fumito Toda,Yuichi Okazaki

doi:10.2320/matertrans.mt-mg2022021

Abstract

Chemical substitution is an effective way to improve electrocatalytic properties in transition metal oxides. We investigate the synergistic effect between Fe4+ and Co4+ ions on the catalytic activity for oxygen evolution reaction (OER) in the Fe-Co-mixed perovskite oxide CaFe1–xCoxO3. The OER activity of CaFe1–xCoxO3 is substantially increased by small amounts of Co (Fe) doping into CaFeO3 (CaCoO3), leading to the superiority compared to the pure Fe and Co perovskite oxides. The x dependences of the OER overpotential and specific activity for CaFe1–xCoxO3 (0.05 ≦ x ≦ 0.95) are expressed by constant offset from the weighted average between CaFeO3 and CaCoO3, which can be interpreted to be the synergistic effect between Fe4+ and Co4+ ions on OER activity. The absence of the optimum x for the highest activity for CaFe1–xCoxO3 contrasts with the volcano-like plots reported in various mixed-metal oxides. First-principle calculations using the special quasirandom structure models on CaFe1–xCoxO3 (x = 0.03–0.5) demonstrate that about half the amount of Fe4+ is electronically activated to possess smaller charge-transfer energies, corroborating the enhancement of catalytic activity in CaFe1–xCoxO3. These findings provide new insight into the synergistic effects in complex transition metal oxide catalysts.

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