Mechanism of Nickel–Iron Water Oxidation Electrocatalysts

Abstract

Hotly debated these days is whether nickel or iron is the active site in nickel–iron water oxidation electrocatalysts. We have previously argued that iron is a likely candidate for highly active materials because it can reach high-oxidation (high-ox) states at potentials relevant to water splitting. Here, we further assert that nickel is likely not an active site for water oxidation electrocatalysis in these materials. Our 3-fold argument is supported by electrochemical measurements on rigorously planar electrodes produced by pulsed laser ablation in liquids: (1) nickel cannot achieve high-ox states in aqueous environments at relevant potentials; (2) large steady-state concentrations of metal sites preclude them from being active, thereby indicating that even more oxidizing moieties are critically important; and (3) unlike nickel sites, high-ox iron sites documented experimentally are neither rare nor unreasonably reactive.

2021 Pioneers in Energy Research: Vivian Yam

“…The article of Xie and co-workers presents a dual-engineered nanofibrous composite separator with a Janus structure to both physically and chemically block LiPS shuttling in Li–S batteries. Winkler, Gray, and Hunter assert that nickel is likely not an active site for water oxidation electrocatalysis in nickel–iron water oxidation electrocatalysts, suggesting high-oxidation iron species as the likely active intermediates in water oxidation catalysis.…”

Direct Detection of FeVI Water Oxidation Intermediates in an Aqueous Solution

“…Unfortunately, the detection of the higher oxidation state of Fe species [Fe V or Fe VI ] was hindered. This is because, in the high‐rate water oxidation cycle, the high‐valent active center reacts rapidly with H 2 O/OH − and is quickly depleted, resulting in a steady‐state concentration below the detection limit of the spectroscopic equipment [4b, 6] . To overcome this problem, Gray et al [10] .…”

Morphology-Controlled Nickel Oxide and Iron–Nickel Oxide for Electrochemical Oxygen Evolution Reaction

“…Many studies have focused on the excellent OER activity of nickeland nickel−iron-based materials; however, few have experimentally observed the crystal planes of nickel oxide and iron− nickel oxide. 21,22 Herein, we synthesized various morphologies of nickel oxide, namely octahedral ((111) facet exposed), hexagonal ((110) facet exposed), and donut-shaped synthesized via the Kirkendall effect as illustrated in Scheme 1. In addition, a small amount of iron was added to the nanoparticles using two methods: doping and post-deposition.…”