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 BPMPDCu2 and BPMANCu2) than that with a longer distance (below 80% for 6-HPACu2) in an aqueous solution (pH 7.0). Notably, the catalytic activity of BPMPDCu2 is 11 times and 237 times faster than those of 6-HPACu2 and BPMANCu2, respectively, which does not correlate directly with their Cu···Cu distances. Further investigations into low-valent LCuI2 intermediates, supported by DFT calculations, indicate that the oxygen binding process is the rate-determining step under electrocatalytic conditions and is sensitive to the CuI···CuI distance. The closest BPMANCuI2 characterized by strong CuI-CuI interactions and the more distant 6-HPACuI2 with its separated dicopper sites both hinder effective O2 binding. In contrast, BPMPDCuI2 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.