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 hindered the performance improvement of self-breathing zinc–air batteries (ZABs), especially in harsh environments with 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 spectroscopy and density functional theory (DFT) calculations collaboratively reveals that the PO 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) display 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 a temperature of −20 °C. 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 environments.