Revealing the unexpected interfacial promotion effect of Cu3P on NiOx/black phosphorus for (photo-)electrocatalytic urea oxidation

Abstract

Up to now, nickel-based materials have been considered as the most promising catalysts for urea oxidation reaction (UOR). However, the inevitable self-oxidation from Ni²⁺ to Ni³⁺ severely limited their activity during UOR. To trigger the UOR occurred before self-oxidation of Ni species by altering reaction pathways, here synergistic dual-site of Cu₃P-NiO_x on black phosphorus (BP) nanosheets is constructed by a facile self-designed electrosynthesis method, where exfoliation of bulky BP into nanosheets and formation of multivalent Ni or Cu precursor are both obtained during electrosynthesis process. The best Cu₃P-NiO_x/BP shows the potential of 1.378 V under light irradiation at 10 mA cm⁻² (without IR compensation), 187 mV lower than that in oxygen evolution reaction. This UOR activity of Cu₃P-NiO_x/BP is superior to Cu₃P/BP or NiO_x/BP, which is attributed to synergistic dual-site constructure of Cu₃P-NiO_x. In-situ and ex-situ characterizations suggest that in-situ generated Cu₃P promotes adsorption and activation of urea molecules, and takes synergistic effect with NiO_x, which makes urea oxidation undergoes a direct complete oxidation process. Moreover, with application of light illumination, excited photoelectrocatalytic effect by Cu₃P further greatly enhances the activity for UOR. This study provides insights to the designing principles for optimizing reaction pathways toward small nucleophile molecule oxidation and effective strategies to develop efficient UOR photoelectrocatalysts.