Nickel foam (NF) can be directly utilized as an electrochemical electrode because of its conductive, rigid and porous structure. Herein, a novel robust binder-free Fe–Ni hydroxide-loaded NF electrode is prepared by simple corrosion of NF in a home-made piranha solution with an Fe³⁺ precursor. The roughened NF surface observed after the sample treatment indicates the formation of active species associated with amorphous Fe-hydroxide and/or FeNi-hydroxide particles. The piranha solution-corroded NF electrode generates more hydroxide groups compared to the water-corroded NF electrode, and exhibits remarkable electrochemical oxygen evolution reaction activity in alkaline medium with a low overpotential of 245 mV at 10 mA cm⁻². It also maintains low working potential below 267 mV at 10 mA cm⁻² over 500 h operation without any sign of degradation, indicating excellent long-term stability, which can be attributed to the robust binder-free electrode and the cooperative synergistic interaction between Fe-hydroxides and Ni-hydroxides in the FeNi hybrid composite of individually incompetent OER components, generated over the NF. The role of Fe doped in Ni(OH)₂ is theoretically studied by DFT calculations, and it is found that the adsorption free energies of OH* and OOH* are significantly reduced by the addition of Fe into Ni(OH)₂, accelerating the OER compared to bare Ni(OH)₂. Furthermore, when the active electrode is equipped with a solar cell, a high current density of 23–24 mA cm⁻² is observed for 10 h under AM 1.5G 1 sun irradiation, suggesting high possibility for the production of green hydrogen from renewable solar energy.