Bimetallic Synergy in Oxygen Reduction: How Tailored Metal-Metal Interactions Amplify Cooperative Catalysis

Bimetallic cooperative catalysis, inspired by cytochrome c oxidase and multicopper oxidase, plays a crucial role in the development of four-electron oxygen reduction catalysts. The distance between metals is a crucial factor affecting the cooperative effect, but its precise influence on bimetallic cooperativity in selective oxygen reduction catalysis still awaits an in-depth understanding. Herein, we employ a series of dicopper complexes with varying linkers to systematically adjust the Cu···Cu distance for electrocatalytic oxygen reduction. Structure-activity relationship analyses reveal that catalysts with a shorter dicopper center exhibited significantly higher four-electron selectivity (approaching 100% for BPMPDCu and BPMANCu) than that with a longer distance (below 80% for 6-HPACu) in an aqueous solution (pH 7.0). Notably, the catalytic activity of BPMPDCu is 11 times and 237 times faster than those of 6-HPACu and BPMANCu, respectively, which does not correlate directly with their Cu···Cu distances. Further investigations into low-valent LCu^I₂ intermediates, supported by DFT calculations, indicate that the oxygen binding process is the rate-determining step under electrocatalytic conditions and is sensitive to the Cu^I···Cu^I distance. The closest BPMANCu characterized by strong Cu^I-Cu^I interactions and the more distant 6-HPACu with its separated dicopper sites both hinder effective O₂ binding. In contrast, BPMPDCu^I₂ maintains an optimal Cu···Cu distance that facilitates O₂ binding and ensures robust bimetallic cooperativity throughout the catalytic cycle. This work underscores the significance of metal-metal distance regulation in bimetallic cooperatively selective oxygen reduction and provides valuable insights for the rational design of high-performance oxygen reduction catalysts.