Oxygen Reduction Reaction Activity of Mesostructured Cobalt-Based Metal Oxides Studied with the Cavity-Microelectrode Technique

Abstract Cobalt oxides are known as abundant and stable catalysts for the oxygen reduction reaction (ORR) in an alkaline environment. Here, the ORR activity of Co3O4 and mixed metal oxides NiCo2O4 and CuCo2O4 was studied. Synthesis by using the nanocasting procedure resulted in a mesostructured spinel phase with uniform morphology and high surface area. However, the evaluation of the specific activity of this material class is often hampered by limitations in determining the real surface area. The cavity-microelectrode technique did not require the addition of any additives to the catalytic material. Thus, measuring the double layer capacitance was used to assess the surface area. This approach showed comparable and reliable values for all samples and different cavity depths. Furthermore, the in situ derived surface area enabled the determination of the specific ORR activity, which is more accurate than utilizing the geometric and nitrogen absorption derived surface area. Although the activity of Co3O4 was rather low, the presence of Ni2+ and Cu2+ in the mixed metal oxides led to a substantial activity enhancement, possibly by providing additional active sites