Operando Investigation of Structural and Chemical Origin of Co3O4 Stability in Acid under Oxygen Evolution Reaction.

Replacement of an expensive anode electrocatalyst in proton exchange membrane water electrolysis is of great importance. Recently explored Co3O4 shows good activity and stability toward oxygen evolution reaction (OER) in acid; however, the stability is not adequately explained. Lack of such information delays the design of an acid-stable OER electrocatalyst. Here, we investigate the structural origin of cobalt dissolution by various local atomic configurations of Co3O4. Operando Raman studies and voltammetric data reveal that chemical reduction of the CoO2 intermediate accompanied by lattice oxygen loss leads to undercoordinated CoO sites, which then react with water and form an amorphous three-dimensional (3D) porous network of CoO(OH)x, called the hydrous oxide layer (HOL). Growth of HOL mainly depends on the oxygen vacancies and near-surface OI- that impair the crystalline integrity and favor dissolution. These insights provide a fundamental relation between OER activity and stability and offer a specific guideline for the electrocatalyst design.