Deep eutectic solvent-induced controllable synthesis of bifunctional Ni–Fe–P catalysts for electrochemical water splitting

Developing electrocatalysts with excellent activity, high stability, and low cost is vital for large-scale hydrogen production through electrochemical water splitting. Herein, a bifunctional Ni–Fe–P catalyst in situ grown on Fe foam (Ni–Fe–P/FF) is developed by a simple one-step solvothermal process in the deep eutectic solvent (DES) of ethylene glycol and choline chloride (named Ethaline). The unique solvent environment of Ethaline assisted with the regulating effect of the introduced Fe(III) ions shows an essential role in governing the preparation process. The developed Ni–Fe–P/FF acts as the efficient bifunctional electrocatalyst for water splitting in 1.0 M KOH, requiring overpotentials of 82 mV (229 mV) and 263 mV (370 mV) to deliver 10 mA cm⁻² (100 mA cm⁻²) for oxygen and hydrogen evolution reactions, respectively. Furthermore, the self-supported catalyst-assembled electrolyzer also exhibits good catalytic performance with a low voltage of 1.83 V to drive 100 mA cm⁻² and good stability over 100 h. This work offers a facile approach to fabricating high-performance bifunctional Ni–Fe–P electrocatalysts to catalyze water splitting.