Engineering the electronic structure of perovskite oxide surface with ionic liquid for enhanced oxygen reduction reaction

Perovskite oxides have been intensively studied for electrochemical catalysis, due to their tunable composition, low cost, and strong structure-activity relationship. Here we report a novel and facile strategy to enhance the ORR activity and stability of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) perovskite oxide through engineering the surface electronic structure with ionic liquid (IL). BSCF-IL shows a boosted intrinsic activity similar to 2.7 times that of BSCF, with a positively shifted half-wave potential by 40 mV and significantly improved stability. The enhancement is attributed to the strong electronic interaction between BSCF and IL, which triggers the surface amorphization and selective elemental preservation, promoting the exposure of active sites. Synchrotron-based X-ray absorp-tion spectroscopy and density functional theory calculations reveal the charge transfer from BSCF to IL and the oxidation of surface Co and Fe, leading to the optimized eg filling, lifted O-2p band center and improved metal 3d-O 2p hybridization, contributing to higher ORR catalysis.