High performance binder-free Fe–Ni hydroxides on nickel foam prepared in piranha solution for the oxygen evolution reaction

Abstract

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.