Silver/Nickel Oxide (Ag/NiO) Nanocomposites Produced Via a Citrate Sol-Gel Route as Electrocatalyst for the Oxygen Evolution Reaction (OER) in Alkaline Medium

A series of Ag/NiO nanocomposite electrocatalysts, with a general molecular formula of Ag x Ni 1 − x O, was synthesised employing the citrate sol-gel route and tested for the oxygen evolution reaction (OER) in 0.1 M KOH solution. Crystal structure, morphology and stoichiometry of the catalysts were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The face-centred cubic (fcc) crystalline structure of NiO was revealed as being dominant, having an average crystallite size of 9.6 nm. SEM revealed a non-uniform, cotton-like surface for NiO showing aggregation of particles. Crystallinity of the different synthesised compounds decreased as the Ag content increased. The maximum OER activity was observed for pristine NiO, without any Ag additive, requiring an overpotential of only 263 mV to obtain a current density of 10 mA cm −2 at 25 °C. The addition of Ag inhibited the OER electrocatalytic activity, which might be due to Ag oxidation being observed at 1.431 V. Graphical Abstract ᅟ