Nickel-iron alloy films electrodeposited from metal salt-l-serine deep eutectic solvent for alkaline oxygen evolution reaction

Abstract

Active and stable electrocatalysts for oxygen evolution reaction (OER) is crutial in the widespread application of hydrogen production from water electrolyzers. Here, deep eutectic solvents formed from metal chlorides and l-serine are utilized as the electrolyte to deposit metal films (Ni, Fe, and Ni-Fe alloys) under potentiostatic conditions onto nickel foam (NF) substrate. The deposited films are characterized, and the Ni-Fe alloy films constituting of nanometer-sized crystalline regions. Electron interaction between Ni and Fe is observed. In 1 M KOH, Ni-Fe/NF requires only 219 mV overpotential to achieve a current density of 10 mA cm⁻², and can stably catalyze OER in alkaline solutions. Compared to the Ni/NF and Fe/NF, the high OER activity of Ni-Fe/NF is not originated from improved number of active sites, but from the enhanced intrinsic activity, evidenced by the improved OER kinetics caused by the electron interaction. The acidity of the Ni site increases due to the introduction of Fe, and lattice oxygen mechanism is involved in the OER process on Ni-Fe/NF. After long-term OER, metal oxides and (oxy)hydroxides are formed at the surface.