Multifunctional role of Thiourea in engineering electrodeposited NiFe catalysts for efficient and durable oxygen evolution reaction

Electrodeposition is a cost-effective method to fabricate water splitting catalysts, but achieving uniform nanostructure and durable electrodeposits remains challenging. In this study, Ni-Fe oxyhydroxide catalyst were electrodeposited on Ni foam via two-step metal dissolution electrodeposition (MDE) process in an ethylene glycol-water electrolyte with varying thiourea concentration (0∼0.15 M). The effect of thiourea on nucleation behavior, deposit morphology, composition, and oxygen evolution reaction (OER) performance was investigated using electrochemcial measurements and structural characterization. Thiourea profoundly affected the electrodeposition process. It shifted the nucleation mode from instantaneous to progressive, resulting in more uniformly distributed nanostructures. As a leveling agent, thiourea inhibited excessive deposition in high field regions, and as complex agent, it selectively promoted Ni²⁺ deposition, while suppressing Fe²⁺ incorporation. The optimum thiourea concentration (0.05 M) produced a catalyst with an OER overpotential of 286 mV at 100 mA/cm² and a charge transfer resistance of 1.03 Ω, dramatically improved from 360 mV at 100 mA/cm² and 21.6 Ω without thiourea. The addition of thiourea also increased the electrochemical active surface area and decreased the Tafel slope, indicating improved kinetics. In addition, the 0.05 M thiourea modified catalyst showed excellent durability, with no degradation in performance after 100 h at 100 mA/cm². Thiourea is critical additive that enables controlled nucleation, selective metal deposition dramatically improves the nanostructure, activity, and durability of Ni-Fe OER catalyst, offering promising strategy for high-efficient water electrolysis.