Improved Activity of PdO Supported over Co₃O₄ in the Electrocatalytic Oxygen Evolution Reaction in a Wide pH Range

Abstract

Palladium­(II) oxide supported over Co3O4 was studied as an electrocatalyst for oxygen evolution reaction (OER) in acid, neutral, and alkaline solutions. Co3O4 has limited stability to an alkaline solution, while PdO stability goes from alkaline to slightly acidic pH. The combination of both materials was envisioned to improve the OER activity and stability in a wide range of electrolyte pH. Co3O4 and PdO@Co3O4 were synthesized by a solvothermal method using urea. PdO was deposited as small spheres on the surface of Co3O4 (8.9 wt % of Pd) and caused changes in the Co3O4 spinel structure as compared to the pure oxide, such as structural defects, change in morphology, decrease of the crystallite size, and increase of the surface area and Co3+/Co2+ ratio, and allowed the oxidation of Co4+ from Co3+. Furthermore, PdO@Co3O4 showed higher electrical conductivity, which contributed to the lower overpotential achieved at a current density of 10 mA cm–2 (η10) in all pH solutions. In pH 14, η10 for PdO@Co3O4 was 389, 46 mV lower than Co3O4. The superior OER activity after PdO@Co3O4 can be due to the lower charge-transfer resistance provided by the noble metal and by the higher electron-transfer kinetics shown by the lower Tafel slopes.