Transition Metal Complexes with Macrocyclic Ligands Serve as Efficient Electrocatalysts for Aprotic Oxygen Evolution on Li₂O₂

Abstract

Since the oxygen evolution reaction (OER) in aprotic Li ion electrolytes is a crucial reaction in the charging process of nonaqueous aprotic Li–air batteries, there is a strong demand for decreasing the overpotential by developing more efficient OER catalysts. Herein, we investigated the effect of addition of transition metal complexes with macrocyclic ligands, such as porphyrins and phthalocyanines, for OER in aprotic Li ion electrolytes. Electrochemical experiments using a three-electrode system revealed that such complexes functioned as efficient OER catalysts, in which the center metal in the complex played an essential role in the catalytic process. Among the metal complexes studied, cobalt <i>tert</i>-butylphthalocyanine was found to be the best catalyst: the charging potential was lowered from 4.1 V to about 3.4 V at 1 μA/cm² by addition of 1 mM catalys