Mixed Spinel Ni–Co Oxides: An Efficient Bifunctional Oxygen Electrocatalyst for Sustainable Energy Application
Sreya Roy Chowdhury, Apurba Ray, Sourabh S. Chougule, Jiho Min, A. Anto Jeffery, Keonwoo Ko, Yunjin Kim, Sachindranath Das, Namgee Jung
Abstract
Ni–Co oxides with varying Ni:Co ratios have been synthesized following a facile sol–gel procedure. The influence of variation in composition on the electrocatalytic activity of Ni–Co oxides (Ni:Co = 1:1, 1:2, 1:3, and 1:4) for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is explored in high-pH media. The lattice structure, size, morphology, and surface composition of the synthesized nanocatalysts have been carefully verified by using X-ray diffraction and various microscopic and spectroscopic techniques. Among the synthesized catalysts, the Ni–Co oxide with Ni:Co = 1:3 exhibits the best electrochemical performance with onset potentials of 0.86 and 1.51 V for ORR and OER, respectively. Furthermore, it demonstrates a small potential difference (0.82 V) between the potential corresponding to 10 mA cm–2 current density for OER and the half-wave potential for ORR. The catalyst exhibits admirable catalytic capability, almost comparable to that of the benchmark Pt/C catalyst and rivalling that of the IrO2/C catalyst for OER. This work shed light on the development of a highly active non-precious metal-based energy conversion catalyst and the effect of variation of compositional ratios on the electro-catalytic performance, which will further help rationally design efficient electrocatalysts for sustainable energy applications.