Nanocrystalline Co0.85Se Anchored on Graphene Nanosheets as a Highly Efficient and Stable Electrocatalyst for Hydrogen Evolution Reaction

For the first time, a porous and conductive Co 0.85 Se/graphene network (CSGN), constructed by Co 0.85 Se 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 Co 0.85 Se, 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 Co 0.85 Se. CSGN has a very low Tafel slope of 34.4 mV/dec, which is much lower than that of unhybridized Co 0.85 Se (41.8 mV/dec) and is the lowest ever reported for Co 0.85 Se-based electrocatalysts. CSGN delivers a current density of 55 mA/cm 2 at 250 mV overpotential, much larger than that of Co 0.85 Se (33 mA/cm 2 ). 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.