Nickel-Induced Activation of Iron Foam for the Oxygen-Evolution Reaction: A Multimodal Study of Structure and Dynamics.

Iron/nickel (hydr)oxides are widely recognized as efficient catalysts for the oxygen-evolution reaction (OER) in alkaline media. In this study, the effect of Ni on Fe foam toward OER activity is investigated. Treatment with nickel(II) nitrate induces the emergence of oxidation and reduction peaks, whose intensity and position are modulated by the nickel concentration on the iron foam surface. Remarkably, the OER onset potential exhibits a 240 mV reduction in overpotential upon the incorporation of nickel ions. In-situ Raman spectroscopy reveals the formation of γ-NiO(OH) during OER. Although substantial Fe ions are incorporated into the nickel (hydr)oxide matrix, reduced OER activity and a negative potential shift in the Ni(II)/(III) peak suggest Fe leaching during OER. Based on our findings, we propose a structure featuring multiple active sites, including nickel-doped iron hydroxide, iron oxide, nickel hydroxide, and mixed nickel/iron hydroxides with varying stoichiometries. This work highlights nickel-induced activation of iron foam to enhance OER performance, offering valuable insights for designing advanced, cost-effective, and durable electrocatalysts for applications such as water splitting and renewable energy storage systems.