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

: Loos, S.; Zaharieva, I.; Chernev, P.; Lißner, A.; Dau, H.


ChemSusChem. Chemistry & sustainability, energy & materials 12 (2019), No.9, pp.1966-1976
ISSN: 1864-5631
ISSN: 1864-564X
Journal Article
Fraunhofer IFAM, Institutsteil Pulvermetallurgie und Verbundwerkstoffe Dresden ()

Facile electromodification of metallic NiFe alloys leads to a series of NiFe oxyhydroxide surface films with excellent electrocatalytic performance in alkaline water oxidation. During cyclic voltammetry and after sudden potential jumps between noncatalytic and catalytic potentials, Ni oxidation/reduction was tracked with millisecond time resolution by a UV/Vis reflectance signal. Optimal catalysis at intermediate Ni/Fe ratios is explained by two opposing trends for increasing Fe content: a) pronounced slowdown of the Ni 2+ /Ni 3+ oxidation step and b) increased reactivity of the most oxidized catalyst state detectable at catalytic potentials. This state may involve an equilibrium between Ni 4+ ions and Ni 2+ ions with neighboring ligand holes, possibly in the form of bound peroxides.