Electron redistribution and proton transfer induced by atomically fully exposed Cu-O-Fe clusters coupled with single-atom sites for efficient oxygen electrocatalysis

Single-atom catalysts have garnered significant attention by showing sparkling performance in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) on the air cathode side of energy devices such as metal-air batteries and fuel cells. This work presents a novel catalyst, AC-CuFe-NC, that incorporates Fe-doped CuO atomic clusters (CuOFe) synergistically with single-atom sites. The AC-CuFe-NC demonstrates outstanding ORR performance (half-wave potential of 0.92 V) and an oxygen overpotential gap between ORR and OER as low as 0.61 V, which is among the top reported performances. Combined with in situ ATR-SEIRAS and DFT calculations, it is shown that the synergistic CuOFe atomic clusters are effective in inducing the electronic structure redistribution of the Fe single-atom site, modulating oxygen adsorption energy, and lowering ORR barriers. More importantly, it is revealed that the synergistic adsorption of clusters and single-atom sites establishes hydrogen bonds between the oxygenated intermediates and the electrolyte H2O molecules. The constructed hydrogen bond can provide a pathway for efficient proton transport as supported by kinetic isotope experiments, leading to a substantial enhancement in reaction kinetics. Additionally, the oxygenated intermediates are stabilized, and the Fe-O bond is elongated during the final step of ORR, thereby facilitating the desorption of OH*. The excellent bifunctional electrocatalytic performance of AC-CuFe-NC enable it to show promising application in rechargeable Zn-air batteries. The innovative catalyst structure and synergistic mechanism demonstrated in this study shed light on the development of high-performance catalysts in energy devices.