Facile Synthesis of Graphene Aerogel Supported Nickel/Nickel Oxide Core–Shell Nanoparticles: Efficient Electrocatalysts for Oxygen Evolution Reactions

Graphene aerogels decorated with nickel/nickel oxide core–shell nanoparticles are synthesized via a one-pot hydrothermal reaction followed by thermal reduction. Nickel loading is varied from 1.5 to 40 wt % in a highly controlled fashion by simply tuning Ni 2+ to graphene oxide ratio in the hydrothermal reaction mixture. In fact, graphene aerogel loaded with 40 wt % Ni has a BET surface area of 560 m 2 g –1 due to the preservation of the porous structure with the aid of supercritical CO 2 drying. The thermal reduction applied for the growth of nanoparticles induces deoxygenation of graphene aerogel structure simultaneously. Valence band spectroscopy results reveal an increase in metallicity with a gradual increase in the nickel loading, which has a direct impact on the final electrocatalytic performance. For the evaluation of the electrocatalytic activity of Ni/NiO loaded aerogels toward oxygen evolution reaction, cyclic voltammetry (coupled with a rotating disk electrode) is utilized. In fact, 40 wt % Ni loaded graphene aerogel requires a low overpotential of 320 mV for the supply of 10 mA cm –2 (with a Tafel slope of 61 mV dec –1 and a TOF of 0.11 s –1 ), which outperforms most of the Ni-based electrocatalysts reported in the literature.