Unraveling Oxygen Evolution on Iron-Doped β-Nickel Oxyhydroxide: The Key Role of Highly Active Molecular-like Sites.

The active site for electrocatalytic water oxidation on the highly active iron(Fe)-doped β-nickel oxyhydroxide (β-NiOOH) electrocatalyst is hotly debated. Here we characterize the oxygen evolution reaction (OER) activity of an unexplored facet of this material with first-principles quantum mechanics. We show that molecular-like 4-fold-lattice-oxygen-coordinated metal sites on the (1̅21̅1) surface may very well be the key active sites in the electrocatalysis. The predicted OER overpotential (ηOER) for a Fe-centered pathway is reduced by 0.34 V relative to a Ni-centered one, consistent with experiments. We further predict unprecedented, near-quantitative lower bounds for the ηOER, of 0.48 and 0.14 V for pure and Fe-doped β-NiOOH(1̅21̅1), respectively. Our hybrid density functional theory calculations favor a heretofore unpredicted pathway involving an iron(IV)-oxo species, Fe4+=O. We posit that an iron(IV)-oxo intermediate that stably forms under a low-coordination environment and the favorable discharge of Ni3+ to Ni2+ are key to β-NiOOH's OER activity.