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. Fe4+
species were detected in the NiFe hydroxide catalyst during steady-state water oxidation …