Iron Is the Active Site in Nickel/Iron Water Oxidation Electrocatalysts

Abstract

Efficient catalysis of the oxygen-evolution half-reaction (OER) is a pivotal requirement for the development of practical solar-driven water splitting devices. Heterogeneous OER electrocatalysts containing first-row transition metal oxides and hydroxides have attracted considerable recent interest, owing in part to the high abundance and low cost of starting materials. Among the best performing OER electrocatalysts are mixed Fe/Ni layered double hydroxides (LDH). A review of the available experimental data leads to the conclusion that iron is the active site for [NiFe]-LDH-catalyzed alkaline water oxidation.

Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts

“…[10] Hunter et al reported evidence of Fe 6+ under anodic bias in non-aqueous electrolytes. [14] Co(Fe)O x H y is structurally and electrochemically similar to Ni(Fe)O x H y . [12,13] These,a nd other, results have been used to argue that Fe is the active site in Ni(Fe)O x H y for the OER.…”

Operando X‐Ray Absorption Spectroscopy Shows Iron Oxidation Is Concurrent with Oxygen Evolution in Cobalt–Iron (Oxy)hydroxide Electrocatalysts

“…DFT calculations have also pointed to the presence of higher Fe oxidation states (>3+) in Ni(Fe)O x H y during the OER that facilitate catalysis . These, and other, results have been used to argue that Fe is the active site in Ni(Fe)O x H y for the OER …”

Electromodified NiFe Alloys as Electrocatalysts for Water Oxidation: Mechanistic Implications of Time‐Resolved UV/Vis Tracking of Oxidation State Changes

“…Many sources have reported on Fe 3+ and some claim evidence for Fe 4+ by XAS and Mössbauer spectroscopy, but only for the mixed NiFe oxyhydroxide and clearly not in the Fe‐only catalyst. Also Hunter et al . concluded that Fe in higher oxidation states is the active site in NiFe layered double hydroxide OER catalysts.…”