Ni(OH)2/CeO2 heterointerface catalysts for energy-efficient urea electrooxidation

Abstract

The electrochemical urea oxidation reaction (UOR) is an important half-reaction involved in urea electrolyzers and direct urea fuel cells. However, its practical implementation is hindered by sluggish kinetics and catalyst passivation. Herein, we report a facile hydrothermal synthesis of a Ni(OH)₂/CeO₂ hybrid electrocatalyst (molar ratio 2 : 1) that addresses these challenges through a well-engineered heterointerface. X-Ray diffraction (XRD) confirms the phase transition from α-Ni(OH)₂ to β-Ni(OH)₂, while scanning electron microscopy (SEM) and transmission electron microscopy (TEM) reveal the uniform Ni(OH)₂/CeO₂ dispersion and nanoscale morphology. X-Ray photoelectron spectroscopy (XPS) identifies abundant oxygen vacancies and strong electronic coupling between Ni and Ce species. Compared to pristine Ni(OH)₂, CeO₂, and Ni(OH)₂/MnO₂, the Ni(OH)₂/CeO₂ composite exhibits a lower UOR potential of 0.534 V vs. Ag/AgCl to reach 10 mA cm⁻², and a Tafel slope of 105 mV dec⁻¹ signifying its improved electrocatalytic activity. Electrochemical double-layer capacitance measurements reveal a threefold increase in C_dl (610 μF cm⁻²) relative to Ni(OH)₂/MnO₂, indicating a dramatically enlarged electrochemically active surface area. The combination of rapid charge transfer and favorable surface characteristics positions Ni(OH)₂/CeO₂ as a promising catalyst for electrooxidation of urea.