Ni/NiO Heterostructures Encapsulated in Oxygen Doped Graphene as Multifunctional Electrocatalysts for HER, UOR and HMF Oxidation Reaction

Nickel (Ni)/nickel oxide heterostructures have been demonstrated to be promising candidates to replace catalysts based on conventional noble metals for electrochemical water splitting. Here we report a universal, controlled scalable arc-discharge method to produce Ni/NiO nanoparticles encapsulated in graphene as multifunctional catalysts for the hydrogen evolution reaction (HER), urea oxidation reaction (UOR) and 5-hydroxymethylfurfural (HMF) oxidation reaction. We find that the catalytic activity of Ni/NiO@graphene can be altered dramatically by the electronic structure of the graphene layer which can be tuned by introducing oxygen dopants through a post-annealing process. Due to the synergistic effect of Ni nanoparticles, Ni/NiO heterostructures and the oxygen-doped graphene layer, the as-prepared catalysts show superior catalytic activity for the HER and UOR. The overall electrochemical water splitting in alkaline electrolyte with urea only requires 1.46 V. Moreover, the as-fabricated composites can catalyze the HMF oxidation reaction efficiently. This work provides a viable strategy to solve the energy challenge.