Uncovering the role of vanadium doped Ni2P for low concentration urea oxidation

Abstract

• A selective electrocatalyst was developed for the urea oxidation reaction in low-urea-concentration electrolytes • A dual-active site mechanism is proposed for V- doped Ni 2 P to catalyze urea oxidation reaction • Vanadium enhances urea adsorption, alters the rate-determining step, and lowers the energy barrier for urea oxidation reaction • Incorporating vanadium into Ni₂P reduces energy consumption by 40% for complete urea removal Nickel-based electrocatalysts are promising candidates for urea oxidation reaction (UOR). However, they also catalyze the competing oxygen evolution reaction (OER). This competition makes electrocatalytic urea oxidation more energy-consuming, especially in electrolytes with low urea concentrations that resemble the urea levels in actual wastewater samples. Herein, V 5+ is incorporated into the 3D structure of inter-connected nickel phosphide nanosheets grown on the surface of nickel foam (denoted as V-doped Ni 2 P/NF) to enhance the affinity of the nickel phosphide electrocatalyst for urea molecules. In situ Raman and DFT disclosed that vanadium serves as an adsorption site, bringing urea molecules close to the electrode surface. Moreover, upon the addition of vanadium, the rate-determining step (RDS) of the urea oxidation reaction changes from the N 2 desorption step to the first deprotonation with a lower energy barrier (2.62 eV to 2.03 eV, respectively). The synthesized electrocatalyst exhibits outstanding electrocatalytic performance with a low onset potential and long-term durability toward UOR. Additionally, in a low urea concentration electrolyte, the V-doped Ni 2 P/NF demonstrates excellent selectivity for UOR over OER at all applied potentials. Compared to Ni 2 P/NF, the V-doped Ni 2 P/NF shows a 40 % reduction in energy consumption for complete decomposition of urea in a low urea concentration environment.

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