title: Identification of highly active Fe sites in (Ni,Fe)OOH for electrocatalytic water splitting.
abstract: Highly active catalysts for the oxygen evolution reaction (OER) are required for the development of photoelectrochemical devices that generate hydrogen efficiently from water using solar energy. Here, we identify the origin of a 500-fold OER activity enhancement that can be achieved with mixed (Ni,Fe)oxyhydroxides (Ni(1-x)Fe(x)OOH) over their pure Ni and Fe parent compounds, resulting in one of the most active currently known OER catalysts in alkaline electrolyte. Operando X-ray absorption spectroscopy (XAS) using high energy resolution fluorescence detection (HERFD) reveals that Fe(3+) in Ni(1-x)Fe(x)OOH occupies octahedral sites with unusually short Fe-O bond distances, induced by edge-sharing with surrounding [NiO6] octahedra. Using computational methods, we establish that this structural motif results in near optimal adsorption energies of OER intermediates and low overpotentials at Fe sites. By contrast, Ni sites in Ni(1-x)Fe(x)OOH are not active sites for the oxidation of water.
authors.affiliation: Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Mail Stop 976, Berkeley, California 94720, United States.
authors.forename: Daniel
authors.initials: D
authors.lastname: Friebel
authors.forename: Mary W
authors.initials: MW
authors.lastname: Louie
authors.forename: Michal
authors.initials: M
authors.lastname: Bajdich
authors.forename: Kai E
authors.initials: KE
authors.lastname: Sanwald
authors.forename: Yun
authors.initials: Y
authors.lastname: Cai
authors.forename: Anna M
authors.initials: AM
authors.lastname: Wise
authors.forename: Mu-Jeng
authors.initials: MJ
authors.lastname: Cheng
authors.forename: Dimosthenis
authors.initials: D
authors.lastname: Sokaras
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: Roberto
authors.initials: R
authors.lastname: Alonso-Mori
authors.forename: Ryan C
authors.initials: RC
authors.lastname: Davis
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
authors.forename: Jens K
authors.initials: JK
authors.lastname: Nørskov
authors.forename: Anders
authors.initials: A
authors.lastname: Nilsson
authors.forename: Alexis T
authors.initials: AT
authors.lastname: Bell