Decoding Natural Strategy: Oxygen-Evolution Reaction on the Surface of Nickel Oxyhydroxide at Extremely Low Overpotential.

Although nickel (hydr)oxides in the absence of other metal ions are conventionally deemed inefficient catalysts for the oxygen-evolution reaction (OER) under alkaline conditions, this study reveals that nickel oxyhydroxide displays an OER activity at the associated peak for Ni(II) to Ni(III) oxidation postcharge accumulation. This occurs with only 90-120 mV overpotentials (at a low current density) and a Tafel slope of 297 mV/decade in a 0.10 M KOH solution. In the initial seconds, the Faraday efficiency lingers at a relatively low 20%, which can be attributed to charge storage. Nonetheless, as the duration extends to reach the 200 s mark, the efficiency notably escalates, exceeding 80%. Additionally, a mechanism for the OER in this low-overpotential zone is proposed, grounded in our investigation of the Ni(II) to Ni(III) peak and the OER region through in situ Raman spectroscopy. Taking into account the quantity of oxygen generated and the concentrations of redox-active Ni ions in the region of the redox peak, a turnover frequency of at a potential of 4.3 × 10 -4 s -1 at 1.37 V was calculated. The documented reduction in overpotential during the OER may be ascribed to the complex interplay between the process of the OER and charge accumulation. The convergence of these reciprocally influencing factors facilitates a notably low overpotential in the OER. Our findings bear substantial implications for developing highly efficient and stable electrocatalysts for the OER in water-splitting applications.