Sponge Assembled by Graphene Nanocages with Double Active Sites to Accelerate Alkaline HER Kinetics.

Elaborate design of novel hybrid structures for hydrogen-evolution electrocatalysts is a crucial strategy for synergistically accelerating the reaction kinetics of water splitting. Herein, we prepare a three-dimensional (3D) sponge assembled by graphene nanocages (SGNCs) in which Ni nanoparticles and Ni single atoms coexist via a facile one-pot self-templating and self-catalytic strategy. Driven by simultaneous atomization and agglomeration under higher temperature, dual active sites of single atoms and nanoparticles are formed on graphene nanocages. Benefiting from the unique 3D porous structure and dual active sites, the SGNCs exhibit excellent hydrogen evolution reaction (HER) performance, which affords the current density of 10 mA cm at a low overpotential of 27 mV. Theoretical calculations reveal that the interaction between single atoms and nanoparticles promotes HER kinetics. The controlled engineering strategy of non-noble metal-based hybrid materials provides prospects for innovative electrocatalyst development.