N- and S- co-doped graphene sheet-encapsulated Co9S8 nanomaterials as excellent electrocatalysts for the oxygen evolution reaction

The development of highly efficient and earth-abundant electrocatalysts to replace the rare and expensive noble metal catalysts is currently an important goal of renewable energy research. We report advanced and highly efficient electrocatalysis of oxygen evolution reaction using the cobalt sulfide (Co9S8) nanoparticles embedded in nitrogen, sulfur co-doped graphene (Co9S8/NSG) hybrid materials, which are obtained by coating Co-based metal-organic frameworks. The frameworks are grown in situ on graphene oxide using a facile pyrolysis method, with polydiaminothiazole, which serves as both a nitrogen and a sulfur source in the system. The prominent synergistic effect of the S, N-co-doped graphene helps to enhance the conductivity of the hybrid, and the Co9S8 provides abundant catalytic active sites as well as mesoporous structure. As a result, the Co9S8/NSG hybrid materials exhibit outstanding performance in the oxygen evolution reaction and superior stability in alkaline electrolytes. For example, the hybrid materials have a small overpotential of 0.26 V with a Tafel slope of 55 mV dec−1 at a current density of 10 mA cm−2 and they show long-term stability in 1 M KOH. This work provides a general and promising method for the design and synthesis of inexpensive and efficient OER electrocatalysts.