A Regenerable, Electrodeposited, Iron-Group Electrocatalyst for the Oxygen Evolution Reaction

Abstract

Fe-Ni-based oxides and oxyhydroxides have been recognized as interesting oxygen evolution reaction (OER) electrocatalysts, and thus could be alternatives to replace rare and expensive metal oxides (e.g., IrO2 and RuO2) for water electrolysis in the generation of hydrogen to store energy from intermittent sources, such as solar and wind. However, these materials may suffer from deactivation during the OER due to changes in the active phases. In this study, a methodology to regenerate the OER activity of aged, electrodeposited Fe-Ni-Co electrocatalysts in an alkaline electrolyte is presented.The Fe-Ni-Co thin films were electrodeposited over a range of current density from a boric acid electrolyte onto rotating cylinder electrodes (RCE). The resulting deposits had different Fe and Ni compositions, containing a small amount of Co, and were used to characterize the OER in 1 M KOH. Linear sweep voltammetry was used to generate a surface oxide and measure the OER kinetics. The electroactive surface areas were accessed using an electrochemical ferricyanide/ferrocyanide redox reaction. The OER kinetics were found to be a function of deposit composition, with the lowest Tafel slope and overpotential (at 10 mA/cm2) observed at a metal weight percentage ratio, Fe/(Ni+Co), of 1.2. The electrocatalyst became less active upon chronopotentiometric aging at 10 mA/cm2 for 30 hours. Notably, when the aged catalyst was reduced by applying a cathodic current density, the electrocatalytic activity recovered. The spectra of Fe, Ni, Co L-edge and O K-edge from X-ray absorption near edge spectroscopy (XANES) suggested that the aging and recovery are due to the redistribution of the electron density between O, and Fe and Ni. Co was found to be predominately in the metallic state.