Electrochemical Synthesis of Co₃O_4-xFilms for Their Application as Oxygen Evolution Reaction Electrocatalysts: Role of Oxygen Vacancies

Herein we report the synthesis of efficient Co3O4 electrocatalysts toward the oxygen evolution reaction (OER) in alkaline media. Co3O4 films were obtained by thermal treatment of Co electrodeposited from electrolytic solutions containing glycine at different pH values. Co3O4 films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The grain size of the electrocatalysts decreases to 100 nm and the oxygen vacancies content increases, as the pH of the solution was increased during the synthesis. Linear Sweep voltammetry (LSV) and Chronopotentiometry techniques were employed to evaluate the electrocatalytic activity of the films. Co3O4 electrocatalysts obtained at pH values higher than 7 exhibit a better electrocatalytic performance than the obtained at pH values less than 4, such as a potential to reach 1.5 mAcm−2 of 0.6 V and 0.68 mV, respectively. Co3O4 synthesized under alkaline conditions exhibit the best charge transfer resistance with 4.3 Ω during OER electrolysis. The improvement is associated to the presence of oxygen vacancies that promote the activity and stability of the electrocatalysts toward the OER.