Mechanism and Activity of Water Oxidation on Selected Surfaces of Pure and Fe-Doped NiOx

Mixed nickel–iron oxides have recently emerged as promising electrocatalysts for water oxidation because of their low cost and high activity, but the composition and structure of the catalyst’s active phase under working conditions are not yet fully established. We present here density functional theory calculations with on-site Coulomb repulsion of the energetics of the oxygen evolution reaction (OER) on selected surfaces of pure and mixed Ni–Fe oxides that are possible candidates for the catalyst’s active phase. The investigated surfaces are pure β-NiOOH(011̅5) and γ-NiOOH(101), Fe-doped β-NiOOH(011̅5) and γ-NiOOH(101), NiFe 2 O 4 (001), and Fe 3 O 4 (001). We find that Fe-doped β-NiOOH(011̅5) has by far the lowest overpotential (η = 0.26 V), followed by NiFe 2 O 4 (001) (η = 0.42 V). Our results indicate that Fe-doped β-NiOOH and, to a lesser extent, NiFe 2 O 4 could be the phases responsible for the enhanced OER activity of NiO x when it is doped with Fe.