Nanocrystalline CoSe Anchored on Graphene Nanosheets as a Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction.

For the first time, a porous and conductive CoSe/graphene network (CSGN), constructed by CoSe nanocrystals being tightly connected with each other and homogeneously anchored on few-layered graphene nanosheets, has been synthesized by a facile one-pot solvothermal method. Compared to unhybridized CoSe, CSGN exhibits much faster kinetics and better electrocatalytic behavior for hydrogen evolution reaction (HER). The HER mechanism of CSGN is improved to Volmer-Tafel combination, instead of Volmer-Heyrovsky combination, for CoSe. CSGN has a very low Tafel slope of 34.4 mV/dec, which is much lower than that of unhybridized CoSe (41.8 mV/dec) and is the lowest ever reported for CoSe-based electrocatalysts. CSGN delivers a current density of 55 mA/cm at 250 mV overpotential, much larger than that of CoSe (33 mA/cm). Furthermore, CSGN shows superior electrocatalytic stability even after 1500 cycles. The excellent HER performance of CSGN is attributed to the unique porous and conductive network, which can not only guarantee interconnected conductive paths in the whole electrode but also provide abundant catalytic active sites, thereby facilitating charge transportation between the electrocatalyst and electrolyte. This work provides insight into rational design and low-cost synthesis of nonprecious transition-metal chalcogenide-based electrocatalysts with high efficiency and excellent stability for HER.