title: On the chemical state of Co oxide electrocatalysts during alkaline water splitting.
abstract: Resonant inelastic X-ray scattering and high-resolution X-ray absorption spectroscopy were used to identify the chemical state of a Co electrocatalyst in situ during the oxygen evolution reaction. After anodic electrodeposition onto Au(111) from a Co(2+)-containing electrolyte, the chemical environment of Co can be identified to be almost identical to CoOOH. With increasing potentials, a subtle increase of the Co oxidation state is observed, indicating a non-stoichiometric composition of the working OER catalyst containing a small fraction of Co(4+) sites. In order to confirm this interpretation, we used density functional theory with a Hubbard-U correction approach to compute X-ray absorption spectra of model compounds, which agree well with the experimental spectra. In situ monitoring of catalyst local structure and bonding is essential in the development of structure-activity relationships that can guide the discovery of efficient and earth abundant water splitting catalysts.
authors.affiliation: Joint Center for Artificial Photosynthesis, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA. dfriebel@slac.stanford.edu.
authors.forename: Daniel
authors.initials: D
authors.lastname: Friebel
authors.forename: Michal
authors.initials: M
authors.lastname: Bajdich
authors.forename: Boon Siang
authors.initials: BS
authors.lastname: Yeo
authors.forename: Mary W
authors.initials: MW
authors.lastname: Louie
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Miller
authors.forename: Hernan
authors.initials: H
authors.lastname: Sanchez Casalongue
authors.forename: Felix
authors.initials: F
authors.lastname: Mbuga
authors.forename: Tsu-Chien
authors.initials: TC
authors.lastname: Weng
authors.forename: Dennis
authors.initials: D
authors.lastname: Nordlund
authors.forename: Dimosthenis
authors.initials: D
authors.lastname: Sokaras
authors.forename: Roberto
authors.initials: R
authors.lastname: Alonso-Mori
authors.forename: Alexis T
authors.initials: AT
authors.lastname: Bell
authors.forename: Anders
authors.initials: A
authors.lastname: Nilsson