title: Operando Analysis of NiFe and Fe Oxyhydroxide Electrocatalysts for Water Oxidation: Detection of Fe⁴⁺ by Mössbauer Spectroscopy.
abstract: Nickel-iron oxides/hydroxides are among the most active electrocatalysts for the oxygen evolution reaction. In an effort to gain insight into the role of Fe in these catalysts, we have performed operando Mössbauer spectroscopic studies of a 3:1 Ni:Fe layered hydroxide and a hydrous Fe oxide electrocatalyst. The catalysts were prepared by a hydrothermal precipitation method that enabled catalyst growth directly on carbon paper electrodes. Fe(4+) species were detected in the NiFe hydroxide catalyst during steady-state water oxidation, accounting for up to 21% of the total Fe. In contrast, no Fe(4+) was detected in the Fe oxide catalyst. The observed Fe(4+) species are not kinetically competent to serve as the active site in water oxidation; however, their presence has important implications for the role of Fe in NiFe oxide electrocatalysts.
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Jamie Y C
authors.initials: JY
authors.lastname: Chen
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Lianna
authors.initials: L
authors.lastname: Dang
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Hanfeng
authors.initials: H
authors.lastname: Liang
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: Wenli
authors.initials: W
authors.lastname: Bi
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: James B
authors.initials: JB
authors.lastname: Gerken
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Song
authors.initials: S
authors.lastname: Jin
authors.affiliation: Advanced Photon Source, Argonne National Laboratory , 9700 South Cass Avenue, Lemont, Illinois 60439, United States.
authors.forename: E Ercan
authors.initials: EE
authors.lastname: Alp
authors.affiliation: Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
authors.forename: Shannon S
authors.initials: SS
authors.lastname: Stahl