Design of bifunctional air electrodes based on the reaction fields between oxygen reduction reaction and oxygen evolution reaction

Large overpotential is one of the critical issues of bifunctional air electrodes for metal–air secondary batteries and alkaline regenerative fuel cells. To overcome this problem, construction of gas diffusion electrodes providing plenty amount of reaction fields for oxygen reduction and evolution are necessary. In this work, we investigate the reaction fields in the gas diffusion electrodes by comparing the oxygen diffusion resistances in the gas diffusion electrodes with different electrolyte solutions and catalyst layer thicknesses to improve the overpotential of the gas diffusion electrode. It is suggested that the reaction fields for oxygen reduction and oxygen evolution concentrate on the air side and the electrolyte sides of the catalyst layer, respectively. Based on this assignment, we fabricate a gas diffusion electrode where the oxygen reduction and evolution catalysts are, respectively arranged to the air and electrolyte sides of the catalyst layer. This electrode showed both lower overpotential and higher cyclability than those loaded the same catalysts with the opposed and mixed configuration. This result verifies the assignment of the reaction fields and shows the impact of the catalyst arrangement on the activity and the durability of the bifunctional electrodes.