Activity of Water Oxidation on Pure and (Fe, Ni, and Cu)-Substituted Co₃O₄

Co-based oxides have recently emerged as suitable electrocatalysts for the water oxidation reaction due to their low cost and high activity. Here, we present a comparative study of the electrochemical behavior of pure and metal-ion-substituted cobalt oxides, Co 3 O 4 (110) and M x Co 3– x O 4 (110), (M = Fe, Ni, Cu; x = 25% and 50%) in order to elucidate the effect of the cation distribution in the surface of the crystal lattice. We have used density functional theory calculations with on-site Coulomb repulsion of the energetics of the oxygen evolution reaction (OER) on these surfaces, and substantial work has been targeted to understand the relation between structure, mechanism, and activity. The activity of the substituted spinels increases relative to that of pure Co 3 O 4, with a considerable decrease in overpotential values. This agrees well with the experimental findings. We find the activity of the Co-based oxides toward the OER is in the following order where we have considered that O 2 evolution occurs at the substituent site: Fe x Co 3– x O 4 ( x = 50%) (0.77 V) > pure Co 3 O 4 (0.76 V) > Fe x Co 3– x O 4 ( x = 25%) (0.69 V) > Ni x Co 3– x O 4 ( x = 50%) (0.61 V) > Cu x Co 3– x O 4 ( x = 50%) (0.56 V) > Ni x Co 3– x O 4 ( x = 25%) (0.53 V) > Cu x Co 3– x O 4 ( x = 25%) (0.41 V). Our results indicate that 25% Cu-substituted Co 3 O 4 has by far the lowest overpotential value of 0.41 V.