Accelerating Ni ²⁺ /Ni ³⁺ Transformation in PtNi/Ni Heterojunction Rooted on Porous TiO ₂ Nanotubes for Enhanced Urea Electrooxidation

Achieving high current densities with nickel-based catalysts within the urea oxidation reaction (UOR) potential window is critical for the scalable implementation of urea electrolysis. However, their performance is limited by the high energy barriers of Ni2+ deprotonation and sluggish proton-coupled electron transfer (PCET) processes. Herein, ultrafine PtNi-Ni nanoparticles rooted on porous TiO2 (PtNi-Ni/TiO2) nanotubes are constructed by a facile surface segregation and galvanic replacement reaction. The obtained PtNi-Ni/TiO2 electrocatalysts deliver the highest UOR current density of 284.4 mA cm–2 at a low potential of 1.50 V, ranking among the top UOR electrocatalysts reported. Kinetic analysis and theoretical calculations reveal that alloying significantly reduces the free energy for the Ni2+ electrooxidation, while heterojunction engineering promotes the PCET process and weakens the strong adsorption of urea, thereby improving the UOR current density. Moreover, PtNi-Ni/TiO2 delivered hydrogen evolution activity, enabling a urea electrolyzer employing PtNi-Ni/TiO2 as both anode and cathode to achieve 50 mA cm–2 at a low cell voltage of 1.55 V, which reduces the energy consumption by 17.2% compared with water splitting systems. This study provides a fundamental paradigm and insights for designing advanced nickel-based electrocatalysts for urea-splitting systems.