Activity of pure and transition metal-modified CoOOH for the oxygen evolution reaction in an alkaline medium†
A new electrode structure enabling low overpotentials for the oxidation of water, based on three-dimensional arrays of CoOOH nanowires, is presented. The electrocatalytic activities of pure and M-modified cobalt oxyhydroxides (M = Ni or Mn) nanowires have been investigated in detail for the oxygen evolution reaction (OER) in an alkaline environment. The pure, Ni-, and Mn-modified nanowires, with preferentially exposed low-index surfaces, were fabricated directly on stainless steel mesh current collectors using an inexpensive and scalable chemical synthesis procedure. The unique electrode structure ensures excellent substrate–catalyst electrical contact and increases the surface area accessible to the electrolyte. The OER activity of CoOOH nanowires is shown to be significantly improved through incorporation of Ni. Specifically, optimal OER activity is obtained for CoOOH nanowires with 9.7% surface Ni content, which corresponds to four-times greater current density compared to pure CoOOH. In contrast, Mn modification of the CoOOH nanowires did not improve the OER activity. Tafel analysis suggests Ni incorporation leads to change in the OER rate-determining step based on an observed decrease in the Tafel slope. Electrochemical impedance spectroscopy reveals that Ni incorporation improves the ability of the catalysts to stabilize surface intermediates, whereas Mn incorporation impedes intermediate stabilization. This study provides new insights regarding the influence of transition metal impurities on the OER activity of CoOOH and provides a clear strategy for the optimization of CoOOH-based OER catalysts in alkaline electrolytes.