Molybdenum sulfide clusters-nitrogen-doped graphene hybrid hydrogel film as an efficient three-dimensional hydrogen evolution electrocatalyst

Nobel metal-free electrocatalysts for hydrogen evolution reaction (HER) with high activity and low cost are essential for hydrogen production. However, the design and fabrication of such catalysts are still highly challenging thus far. In this work, we fabricate a three-dimensional (3D) hybrid electrocatalyst by decorating N-doped graphene hydrogel film (NG) with molecular clusters (MoS_x). This material has successfully combined the desired merits for electrocatalysis, such as highly active MoS_x sites for HER, excellent mechanical properties for strong catalyst durability, highly hydrated framework for sufficient active site exposure as well as 3D conductive networks for fast charge transport. The 3D electrode shows a remarkable catalytic activity toward HER (140.6mV at 10mAcm^-2), which outperforms most graphene and/or MoS_x-based electrocatalysts reported in the literature. Also, the catalyst electrode demonstrates favorable reaction kinetics (Tafel slope, 105mV dec^-1) and strong durability (seldom performance degradation after 12h or 1000 cycles). Further mechanism study reveals that Volmer reaction is the dominant process on the 3D electrode and the dual active sites are highly probable during electrocatalytic process, that is, pyridinic/pyrrolic structures of N-doped graphene and defects/edges of MoS_x are both active centers.