Cobalt-Coordinated Sulfur-Doped Graphitic Carbon Nitride on Reduced Graphene Oxide: An Efficient Metal-(N,S)-C-Class Bifunctional Electrocatalyst for Overall Water Splitting in Alkaline Media

Development of an efficient, scalable, and cost-effective bifunctional electrocatalyst for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) through overall water splitting is urgently needed to satisfy the demand for sustainable energy. In this work, we demonstrate an outstanding electrocatalytic activity of a unique metal-(N,S)-C class of electrocatalyst composed of cobalt-coordinated sulfur-doped graphitic carbon nitride (Co-SCN) and reduced graphene oxide (RGO) toward overall water splitting in alkaline media. Importantly, the optimized Co-SCN/RGO catalyst exhibits remarkable electrocatalytic activities for both the HER and the OER, with low overpotentials of 150 and 250 mV vs RHE, respectively, at a current density of 10 mA cm^-2. The cell potential required for the overall water-splitting electrolyzer was found to be approximately 1.63 V at 10 mA cm^-2 in a medium of 1.0 M KOH. The activity results obtained for this Co-SCN/RGO electrocatalyst are comparable and in many cases superior to most reported nonprecious-metal-based catalysts in alkaline media. Additionally, stability tests conducted at a constant current density confirm the exceptional durability of the present catalyst over a period of 20 h. The rational strategy demonstrated in the present work provides new insights into the development of high-performance bifunctional electrocatalysts for overall water splitting.