Facile synthesis of graphene aerogel supported nickel/nickel oxide core−shell nanoparticles: efficient electrocatalysts for oxygen evolution reactions

Abstract

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 Ni2+ 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 CO2 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.