Immobilization of Molecular Copper complex and Carboxylate-terminated Co-catalyst on Metal Oxide Electrode for Enhanced Electrocatalytic Oxygen Reduction

Positioning basic/acid groups near molecular catalyst has been become a popular strategy to modulate proton-coupled electron transfer (PCET) reactions in energy conversion and storage. However, the detailed understanding of the real role played by basic/acid groups remains lacking. Here, we report the immobilization of a novel copper (II) dipicolylamine, CuL, catalyst bearing a phosphonic anchor on metal oxide electrode to investigate the activity of oxygen reduction reaction (ORR) in aqueous solution. The catalytic current of ORR by CuL catalyst was significantly enhanced by 3 times as a carboxylate-terminated ligand was integrated onto metal oxide surfaces acting as a co-catalyst. Extensive experimental and theoretical studies reveal that hydrogen bond formed between proximal carboxylate of co-catalyst and Cu-OOH intermediate generated via protonation of Cu-O2 adduct by bulk buffer solution aids O-O bond cleavage, thereby promoting the four-electron four-proton reduction of dioxygen into water reaching a Faradaic efficiency of 97.6%. Our finding is in stark contrast to the typical assignment on the role of basic groups near catalyst that features proton shuttling to facilitate protonation of metal-O2 intermediate forming metal-OOH intermediate. This work offers a new strategy to enhance simultaneously the activity and selectivity of surface-supported non-precious metal electrocatalysts that are important toward realizing alternative energy conversion schemes.