Unraveling eg-band modulation as an alternative strategy to enhance lattice oxygen participation and oxygen electrocatalytic bifunctionality via switching the active site†

Abstract

Lattice oxygen participation is believed to be crucial for enhanced electrocatalytic oxygen evolution reaction activity of perovskite oxides. However, the inherent criterion of an uplifted O 2p-band for lattice oxygen participation makes perovskites prone to elemental leaching and, hence, structural instability. Herein, we report an alternative strategy of e_g-band modulation to enhance the lattice oxygen participation rather than the usual upliftment of the O 2p band. We designed a high-entropy perovskite oxide (HEPO), Ba_0.33Sr_0.66Co_0.165Mn_0.165Ti_0.33Sb_0.33O₃ (BSCMTS), which exhibits enhanced lattice oxygen participation by virtue of modified e_g-band structure despite a downshifted O 2p-band as compared to its Co and Mn only analogs. A switchover of the reaction active center from the lattice oxygen site in the Co-only analog to the Co/Mn metal site in BSCMTS due to the upliftment of e_g-bands of Co/Mn in BSCMTS is believed to be responsible for the enhanced lattice oxygen participation. Moreover, the HEPO also shows one of the best-reported bifunctional oxygen electrocatalytic activities among the pristine perovskite systems and acts as a superior air-cathode electrocatalyst for Zn–air batteries. The study also underscores the importance of the e_g-band structure rather than the usual e_g-electron filling and location of the O 2p and metal d-band center in perovskite oxides for oxygen electrocatalysis.