Low surface energy plane exposed Co3O4 nanocubes supported on nitrogen-doped graphene as an electrocatalyst for efficient water oxidation.

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/cm(2) 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.