Electrodeposits of nickel with reduced graphene oxide (Ni/rGO) and their enhanced electroactivity towards hydrogen evolution in water electrolysis

Catalytic performance of nickel cathodes for hydrogen production by water splitting can be improved by carbon nanomaterials, in particular graphene and reduced graphene oxide (rGO). In this work, electrodeposits Ni/rGO were examined in 0.1 M Na2SO4 with emphasis on hydrogen evolution reaction (HER) and effect of anodic oxidation. Ni and Ni/rGO were electrodeposited by galvanic square wave method with sonication. In contrast to smooth deposits of Ni, deposits of Ni/rGO had the cumulus/cauliflower type morphology with developed surface. Their increased surface area was confirmed by measurements of double layer capacitance. HER and anodic polarization currents were for Ni/rGO significantly higher than those for Ni. Voltammetric cycling or potentiostatic polarization to and above potentials of stability of Ni oxides (Ni3O4, Ni2O3 or NiO2) caused a rise in HER for both materials, but especially strongly for Ni/rGO. Enhanced HER on Ni/rGO was explained by greater surface area and the formation of larger amounts of electrocatalytic Ni oxides/hydroxides, as a result of the increased anodic reactivity of rGO-containing Ni. Incorporated rGO might also contribute by increasing electronic conductivity.