In situ electrochemical transformation of Ni2+ to NiOOH as an effective electrode for water oxidation reaction

Abstract

The poor kinetic background with the four-electron transfer of the oxygen evolution reaction (OER) was eradicated using a nickel-based catalyst, which was identified as an alternative to noble-metal catalysts. Here, we report the simple in situ formation of an earth-abundant nickel oxyhydroxide (NiOOH) electrocatalyst for efficient OER in an alkaline medium. Electroless material preparation, namely, the direct modification of a gas diffusion layer (GDL) with a nickel salt, was studied, and the layered oxyhydroxide phase was found to influence the rate of the OER. Interestingly, complete OER studies were carried out without using any external binders; that is, the catalyst stabilized in an aqueous medium was directly exploited. The resulting in situ electrochemically tuned NiOOH@GDL shows a low overpotential of 294 mV to reach a current density of 20 mA cm⁻², which is superior to most non-noble mono/bimetal oxides that have been studied as OER catalysts so far. The catalyst also shows better kinetics with a low Tafel slope value of 30 mV dec⁻¹ for NiOOH@GDL-B. In addition, the stability of NiOOH@GDL-B was confirmed from a chronoamperometric study that was carried out for 30 h with no significant loss in activity. The electrochemical evolution of the materials was further scrutinized, and a high turnover frequency (TOF) of 1.1 × 10⁻⁴ s⁻¹ was calculated at 300 mV. The consistency of the catalyst was proved with various post-OER characterization analyses, and it appears to be beneficial for developing an efficient electrocatalyst for OER in the near future.