Mixed metal oxides as efficient electrocatalysts for water oxidation

Abstract

Water splitting is a promising reaction for storing sustainable but intermittent energies. The critical bottleneck for it is oxygen evolution reaction (OER) requiring insufficiently low overpotentials, η. Metal oxides are the group of high performance catalysts for water oxidation, so far. We report a facile synthesis of the mixed metal oxide composite (NiO/Mn-doped NiCo2O4) and an easy dip-coating method to create electrocatalysts on nickel foam as electrode substrates cause significant efficiency for OER. The mixed metal oxides catalyst was characterized by using electrochemical methods, high-resolution transmission electron microscopy (HR-TEM), field emission-scanning electron microscopy (FE-SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), inductively coupled plasma (ICP) and fourier-transform infrared spectroscopy (FTIR). Electrocatalysts were shown a Tafel slope of 34 mV dec−1 with overpotential η = 482 mV (for 100 mA cm−2) and at least 20 h durable OER activity. The electrochemical data demonstrate the synergistic effect of the coupling between the three metal-centres of Ni, Co, and Mn to decline the overpotential value. The current of (OER) is related to the electrolyte pH, displaying a non-proton-concerted mechanism in an approach to identifying rate-determining steps for OER. This could be concluded by the direct neighbour lattice O•– coupling to form an O–O bond. The simple and rapid fabrication method and the promising stability and high performance of the herein developed electrodes render them quite promising for technological water splitting systems.