Optimized Ni(ii)-doping in Co(iii)-based layered double hydroxides towards electrochemical oxygen evolution catalysis†

Abstract

An OER catalyst showing both high activity and stability in promoting oxygen evolution is important for its practical application in electrochemical water-splitting. Here, we report the screening of such a catalyst by optimizing the Ni(II)-doping in Co(III)-based layered double hydroxides (LDHs). Such LDH samples tailored with Ni(II)-doping are prepared by an oxidative intercalation reaction where brucite-like Ni(II)_xCo(II)_1−x(OH)₂ (0 ≤ x ≤ 0.50) is reacted with Br₂ in acetonitrile. These samples exhibit a volcano-like trend in OER activity related to the fraction of the dopant. At the optimized doping level (x = 0.20), the activity of the catalyst exceeds that of Ni(II)–Fe(III) LDHs at overpotentials higher than 375 mV. In situ Raman spectroscopy and Fourier-transformed alternating current voltammetry reveal that Ni cations can promote the formation of Co(IV)-oxo intermediates, thereby accelerating the kinetics of the OER. The volcano-like activity trend manifests the underlying synergistic communication between Ni and Co cations.