Nitrogen doped carbon fiber supported nickel phosphide for efficient electrocatalytic overall urea splitting

Abstract

Urea oxidation reaction (UOR) is expected to be one of the effective means to replace oxygen evolution reaction (OER) in specific urea-containing wastewater treatment field. The synchronization of urea electrooxidation and hydrogen production has become an increasingly attractive energy development way. However, UOR faces the challenges of relatively sluggish kinetics and catalyst activity degradation. Here, nitrogen-doped carbon fiber supported nickel phosphide (Ni5P4/NCF-400) is developed as a bifunctional self-supporting electrocatalyst, which is synthesized by electrodeposition and high temperature nitriding. The HER overpotential of Ni5P4/NCF-400 in alkaline medium is 77 mV at 10 mA cm−2, the Tafel value is 98.04 mV dec-1, and the activity does not decrease significantly after continuous hydrogen evolution for 24 h. The UOR potential is 1.376 V at 100 mA cm−2, the Tafel value is 16.45 mV dec-1, and can steadily work at 1.38 V for 48 h. Moreover, Ni5P4/NCF-400 is assembled into a water-urea electrolytic cell device, which could achieve a current density of 40 mA cm−2 at a voltage of 1.67 V and achieve the stability of the catalytic system for 24 h. The excellent electrocatalytic performance of Ni5P4/NCF-400 is attributed to N doping and abundant active sites.