Synergistic Interactions Between Co Nanoparticles and Unsaturated Co-N2 Sites for Efficient Electrocatalysis

Abstract

Transition metal-nitrogen-doped carbon (M-N-C) single-atom catalysts exhibit high activity and stability for the oxygen reduction reaction (ORR). Their electronic structure, crucial for ORR intermediates' adsorption/desorption, can be tuned by altering the coordination environment or integrating small metal nanoparticles. However, synthesizing unsaturated M-NX (x <4) complexes with well-dispersed nanoparticles is challenging due to reactivity and aggregation issues. In this study, a novel plasma-assisted in situ thermal reduction strategy is presented to eliminate unstable surface groups for incorporating highly active Co nanoparticles (NPs) and unsaturated coordinated Co-N2 sites. The unsaturated coordination structure of Co-N2 regulates the electron cloud density around the Co center, decreasing the energy barrier of the rate-determining step of 4e− ORR process; while the Co NPs can accelerate the mass transfer during ORR through enhancing O2 adsorption to promote the desorption of *OH and also facilitate the charge transfer. Thus, the remarkable ORR electrocatalytic activity and durability is achieved simultaneously, leading to excellent performance in an aqueous Zn–air battery. The work opens new directions and possibilities for the design and synthesis of efficient and highly selective electrocatalysts for ORR and other redox reactions.