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• Nickel oxide/nickel carbide/graphene composite was synthesized via one-step thermal treatment. • The graphene increases the conductivity and the distribution of nickel species. • The nickel carbide acts as the active sites for hydrogen evolution reaction (HER). • The NiO improves H 2 O dissociation and HER in the basic solution. • The composite exhibits synergistic electrocatalytic and photocatalytic HER activity. To resolve the energy crisis and environment pollution, it is urgent to explore highly efficient and inexpensive catalysts for hydrogen evolution reaction (HER). In this work, we fabricate nickel oxide/nickel carbide/graphene (labeled as NNG) composite via one-step thermal treatment of NiCl 2 /graphene oxide (GO) as the precursor at relatively low temperature. GO plays a role of the carbon source to form nickel carbide and increases the distribution of the nickel species. The formed nickel carbide acts as the active sites for hydrogen atoms adsorption (H ads). The NiO contacted with the nickel carbide promotes the Volmer reaction: H 2 O+e → H ads +O H -. The two different adsorption sites (nickel carbide for H ads , NiO for OH−) jointly lead to the HER synergistic effect in basic solution. The obtained composites exhibit much higher dye-sensitized photocatalytic and electrocatalytic HER activities than nickel carbide, NiO and RGO alone. The highest apparent quantum yield (AQY) of dye-sensitized hydrogen evolution for NNG12 at 420 nm reaches 39.4%. And the electrocatalytic HER overpotential is -0.28 V at the current density of 10 mA cm-2 in 1.0 mol L-1 KOH. To the best of our knowledge, it is the first time to report nickel oxide/nickel carbide as an efficient HER catalyst in alkaline media. This work paves a way for facile and green fabrication of the efficient HER cocatalysts. [ABSTRACT FROM AUTHOR]