Selenium-Driven Interfacial Engineering of NiMo-Based Electrocatalyst for Efficient Coupled Water Splitting and Urea Oxidation

This study reports the synthesis of a highly efficient and durable bifunctional electrocatalyst, selenium-functionalized NiMo–OH nanosheets (NiMoSe/NF), directly grown on nickel foam (NF) through a two-step hydrothermal process. The resulting rough and interconnected nanosheet morphology significantly enhances electrocatalytic activity toward both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in 1.0 M KOH. The NiMoSe/NF electrode delivers low overpotentials of 240 mV for OER and 269 mV for HER at 100 mA cm–2, with measurement conducted in a three-electrode system to distinguish individual half reactions. When assembled into a two-electrode electrolyzer configuration with NiMoSe/NF serving as both the anode and cathode, overall water splitting and urea electrolysis are achieved at cell voltages of 1.58 and 1.46 V, respectively, at 20 mA cm–2. Separate performance analyses were conducted for OER, HER, and UOR to elucidate individual mechanistic contributions. Furthermore, the electrocatalyst demonstrates excellent long-term stability, maintaining consistent performance over 48 h of continuous operation. Postelectrolysis structural characterization confirms phase retention and surface integrity, addressing common concerns about the stability of selenides in oxidative environments. Mechanistic investigations using electrochemical impedance spectroscopy, temperature-dependent kinetics, and pH-dependent activity reveal that selenium incorporation modulates interfacial charge transfer, enhances proton-coupled electron transfer, and reduces activation energy barriers, contributing to improved catalytic performance under both reductive and oxidative conditions. These findings underscore the importance of electronic and structural tuning in boosting catalytic activity and offer a cost-effective, mechanism-driven strategy for designing robust electrocatalysts for sustainable hydrogen production and urea-rich wastewater treatment.