Surface amorphized in situ RuO-NiFeOOH/Au islands for electrocatalytic oxygen evolution reaction†

Abstract

Hydrogen production via electrocatalytic water splitting is largely impeded by the anodic oxygen evolution reaction (OER). Herein, we report surface amorphized Ru-NiFeP/Au islands as an effective electrode for the OER in 1 M KOH, reaching a current density of 10 mA cm⁻² at 223 mV overpotential. The iR corrected Tafel slope was calculated to be 32 mV dec⁻¹, while electrochemical impedance spectroscopy (EIS) studies revealed a clearly low charge transfer resistance of 0.3 Ω at 400 mV overpotential. The high electrocatalytic activity was attributed to the amorphous nature, reduced band gap, and synergism of Ru-NiFeP with Au. In situ surface-enhanced Raman scattering (SERS) revealed the role of FeOOH at lower overpotentials for facile OH adsorption. The evolution of NiOOH peaks at higher overpotentials for O₂ evolution coupled with synergistic Ru–O bonds to promote the OER was studied with DFT analysis. Bader charge analysis showed that the charge transfer from Fe to O is 0.17 units greater than that from Ni to O for *OH intermediate generation at the active site, and this corroborates the results from in situ SERS studies, where FeOOH is the active site at lower overpotentials. The bond order characteristics become more pronounced when the FeOOH/NiOOH surfaces are accessible. DFT analysis revealed a low free energy change (0.12 eV) for the rate-determining step at the RuO/NiFe-OOH surface.