Ligand effects enhancing low-temperature oxygen reduction kinetics in neutral conditions

Abstract

The sluggish oxygen reduction kinetics, resulting from ineffective O2 activation and hydrogenation, has been hindering the performance improvement of self-breathing zinc-air batteries (ZABs), especially in a hostile environment under low temperatures and low proton concentrations. Herein, we report a series of N-, P-doped carbon catalysts with distinct coordination topologies and structural characteristics. The combination of in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS), in-situ Raman and density functional theory (DFT) calculations collaboratively reveals that the P=O ligands effectively regulate the charge density and spin states around carbon sites, and activate O-O bonds through bridge chemisorption (Yeager model), shifting the reaction kinetics to a favorable reaction pathway. As a result，the P, N co-doped carbon materials (CNP-900) displays remarkable half-wave potentials, fast kinetic and minimal degradation over a wide pH and temperature range. Moreover, flexible zinc-air batteries (FZABs) based on CNP-900 exhibit maximum power densities of 104.2 and 47.1 mW cm-2 under alkaline and neutral conditions, respectively, at temperature of -20 oC. These results provide new perspectives on the kinetic enhancement of metal-free oxygen reduction catalysts, and emphasize the significance of O2 adsorption/activation in harsh reaction conditions.