Strategies for Mitigation of Intermediate CO2 Poisoning to Promote Electrocatalytic Efficiency during Urea Oxidation Reaction

Abstract

Urea electrolysis plays a key role in various urea waste valorization processes. In this regard, the complex six-electron transfer process, urea oxidation reaction, is the key to achieving maximum efficiency. In this study, we developed multilayered α-Ni(OH)₂ sheets through a sonochemical approach. We used Fe³⁺ to dope the α-Ni(OH)₂ sheets in three different compositions. The synthesized catalysts were analyzed by using XRD, SEM, EDX, FTIR, and XPS. Using EDX and XPS, successful doping of iron was confirmed. The electrocatalytic activities were characterized by CV, LSV, EIS, and CA techniques. Through CV analysis, it was identified that Fe³⁺ did not directly participate in the electrochemical reaction; rather, due to high Lewis acidity, it was modulating the electronic environment of Ni²⁺ ions. Iron doping induced a reduction in the onset potential and synergistically increased the catalytic current by promoting a higher number of active sites for urea adsorption. Tafel analysis concluded that the improved reaction kinetics was due to iron incorporation. Using Nyquist and Bode plots, it was identified that iron doping promoted CO₂ production as RDS. Therefore, catalyst poisoning due to prolonged adsorption of CO₂ was diminished, and subsequently, catalyst stability was increased. Overall, while Fe³⁺ doping has proved to be a significant method to enhance catalytic activity, careful optimization of concentration is required to build a state-of-the-art catalytic architecture for urea waste valorization.