Electrochemical deposition of amorphous cobalt oxides for oxygen evolution catalysis

The oxygen evolution reaction (OER) is crucial in water splitting for hydrogen production. However, its high over-potential and sluggish kinetics cause an additional energy loss and hinder its practical application. The cobalt spinel oxide Co₃O₄ exhibits a high catalytic activity for the OER in alkaline solutions. However, the activity requires further enhancement to meet the industrial demand for hydrogen production. This paper presents an electrochemical deposition method to obtain cobalt oxides with a controllable crystallinity on carbon paper (CP). Usually, cobalt oxides grown on CP have a Co₃O₄ spinel oxide structure. The self-supported Co₃O₄/CP exhibited a considerable catalytic activity for the OER. When a VS₂ layer grown on the CP beforehand by a hydrothermal method was used as substrate, the deposited cobalt oxides were in an amorphous state, denoted as CoO /VS₂/CP, which exhibited a higher OER activity and better stability than those of Co₃O₄/CP. The enhancement in the catalytic activity was attributed to the mixture formation of different types of cobalt species, including Co₃O₄, CoO, Co(OH)₂, and metallic Co, because of the reduction by VS₂. We also clarify the significance of the crystallinity of cobalt oxides in the improvement in the OER activity. This process can also be applied to the direct formation of other types of self-supported oxide electrodes for OER catalysis.