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.