Unraveling\nOxygen Evolution on Iron-Doped β‑Nickel\nOxyhydroxide: The Key Role of Highly Active Molecular-like Sites

Abstract

The active site for electrocatalytic\nwater oxidation on the highly\nactive iron­(Fe)-doped β-nickel oxyhydroxide (β-NiOOH)\nelectrocatalyst is hotly debated. Here we characterize the oxygen\nevolution reaction (OER) activity of an unexplored facet of this material\nwith first-principles quantum mechanics. We show that molecular-like\n4-fold-lattice-oxygen-coordinated metal sites on the (1̅21̅1)\nsurface may very well be the key active sites in the electrocatalysis.\nThe predicted OER overpotential (η_OER) for a Fe-centered\npathway is reduced by 0.34 V relative to a Ni-centered one, consistent\nwith experiments. We further predict unprecedented, near-quantitative\nlower bounds for the η_OER, of 0.48 and 0.14 V for\npure and Fe-doped β-NiOOH(1̅21̅1), respectively.\nOur hybrid density functional theory calculations favor a heretofore\nunpredicted pathway involving an iron­(IV)-oxo species, Fe⁴⁺=O. We posit that an iron­(IV)-oxo intermediate that stably forms\nunder a low-coordination environment and the favorable discharge of\nNi³⁺ to Ni²⁺ are key to β-NiOOH’s\nOER activity.