Low Surface Energy Plane Exposed Co₃O₄ Nanocubes Supported on Nitrogen-Doped Graphene as an Electrocatalyst for Efficient Water Oxidation

Abstract

Herein, we report a simple and scalable synthesis of Co₃O₄ nanocubes possessing exposed low surface energy planes supported on nitrogen-doped graphene (Co₃O₄-NC/NGr) by a hydrothermal method as an efficient electrocatalyst for water oxidation. Three different types of morphologies of Co₃O₄ (i.e., nanocubes, blunt edge nanocubes and spherical particles) have been synthesized by systematically varying the reaction time. Subsequently, their catalytic activity toward oxygen evolution reaction (OER) has been screened in alkaline medium. Among the three different morphologies, the intermediate architecture (i.e., the blunt edged nanocubes designated as Co₃O₄-NC/NGr-12h) has shown the highest OER activity. The catalyst displayed an overpotential (η) of ∼280 mV at 10 mA/cm² in 1 M KOH solution, which is lower than that of the other prepared samples such as Co₃O₄-NC/NGr-3h (∼348 mV), Co₃O₄-NC/NGr-9h (∼356 mV), Co₃O₄-NC/NGr-24h (∼320 mV), Co₃O₄-NC/Gr-12h (∼300 mV) and Co₃O₄ (∼310 mV). Along with that, the electrochemical stability of the catalyst is also found to be remarkably good. The role of the low index planes of Co₃O₄ nanocubes (Co₃O₄-NC) and the importance of the doped nitrogen in the carbon framework for the uniform dispersion and direct coupling with Co₃O₄-NC have been examined. The controlled interplay of the exposed crystal planes of Co₃O₄ and its dispersion and synergistic interaction with the nitrogen-doped graphene are found to be the decisive factors in bringing in the modulated OER activity of the system