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), called the hydrous oxide layer (HOL). Growth of HOL mainly depends on the oxygen vacancies and near-surface O^I- 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.