Fe-Incorporated MoO3 Nanorods as Efficient Anodic Electrocatalysts for Urea-Assisted Alkaline and Seawater Oxidation Reactions: Unraveling OER and UOR Interfacial Kinetics via Electrochemical Impedance Spectroscopy and Distribution of Relaxation Time

Abstract Oxygen evolution reaction (OER), characterized by sluggish kinetics and high energy demand, remains a major bottleneck for large-scale hydrogen production, particularly under the challenging conditions of seawater electrolysis. Herein, Fe-incorporated MoO3 nanorods are successfully synthesized via a facile one-pot hydrothermal route, where the Fe content is systematically optimized to enhance electrocatalytic activity. Among the prepared catalysts, FeM15 exhibits superior performance toward both the OER and the urea oxidation reaction (UOR) in alkaline and natural seawater electrolytes. FeM15 achieves low OER overpotentials of 264 and 306 mV at 10 mA cm–2 in 1 M KOH and seawater electrolytes, respectively, along with excellent long-term stability. Replacing OER with UOR significantly reduces the anodic energy requirement, lowering the operating potential by 148 mV in alkaline electrolyte and 184 mV in alkaline seawater. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analyses reveal that OER is governed by sluggish multistep interfacial processes, whereas UOR proceeds through accelerated charge-transfer kinetics with lower polarization resistance and relaxation time. Despite the complex ionic environment of seawater, urea-assisted electrolysis effectively mitigates kinetic limitations and substantially enhances anodic reaction efficiency. These findings highlight FeM15 as a promising and durable electrocatalyst for energy-efficient hydrogen production in both alkaline and seawater electrolysis systems.