Stepwise Electrochemical Construction of FeOOH/Ni(OH)₂ on Ni Foam for Enhanced Electrocatalytic Oxygen Evolution

As the oxygen evolution reaction (OER) is the bottleneck of electrocatalytic water splitting, it is highly imperative to develop OER catalysts with excellent activity and stability. Herein, we demonstrate a stepwise electrochemical construction of crystalline α-FeOOH/β-Ni(OH)₂ composite structure supported on nickel foam (FeOOH/Ni(OH)₂/NF) through cathodic electrodeposition of β-Ni(OH)₂ nanosheets followed by electrophoretic deposition of α-FeOOH nanoparticles. Taking advantange of the synergistic effect of Ni and Fe as well as the formed interface, this composite structure is highly active for the OER process in alkaline media (1 M KOH), providing a very low overpotential of 207 mV versus the reversible hydrogen electrode (RHE) at a geometric catalytic current density of 40 mA cm^-2 and a Tafel slope of 70 mV dec^-1, which is superior to most reported (oxy)hydroxide-based OER electrocatalysts. In combination with density functional theory (DFT) calculations, it is verified that the synergistic interface effect between the real active sites NiOOH and FeOOH can facilitate the OER process. We believe this stepwise electrochemical technique for constructing Ni-Fe (oxy)hydroxide composites can provide new insights into the design and synthesis of highly efficient electrocatalysts for energy conversion applications.