Suppression of Passivation on Nickel Hydroxide in Electrocatalytic Urea Oxidization

Surface passivation of Ni-based electrocatalysts during the electrocatalytic urea oxidization reaction (UOR) renders them impractical and inefficient for applications requiring high current densities. Herein, an efficient strategy to suppress passivation of Ni(OH)_x nanosheets is demonstrated by modulating the near-surface properties using plasma immersion ion implantation, and more importantly, the formation threshold of the UOR-active γ-NiOOH phase is retained. As a result, a remarkable UOR current density of up to 470 mA cm⁻² is achieved from the La ion implanted sample, due to the mitigation of passivation, increase in operando active sites, and acceleration of the catalytic kinetics. By performing a systematic assessment with a multitude of operando, quasi-operando, and time-varying methods, the γ-NiOOH derived from Ni(OH)_x is shown to undergo surface deprotonation at high potentials consequently leading to the occurrence of OER as well as UOR passivation. Furthermore, the implanted La ions are capable of stabilizing protons to sustain UOR. © 2023 Wiley-VCH GmbH.