Convenient synthesis and enhanced urea oxidation of NiO–CrO@N–C

Abstract

Urea oxidation reaction (UOR) can be used as the anode reaction of urea direct fuel cells and for the treatment of urea-containing wastewater. However, to improve the kinetics of the UOR, the development of efficient and cheap catalysts is a key problem to be solved. In this study, mesoporous catalysts (NiO–CrO@N–C) of amorphous NiO and CrO nanoparticles anchored in nitrogen-doped carbon (N–C) were prepared using a sol–gel combined with self-propagating combustion method. Electrochemical tests show that the optimal NiO–CrO@N–C sample has excellent performance against the UOR, that is, the driving voltage is only 1.37 V vs. RHE at a current density (j) of 10 mA cm⁻². After 8 h long-term CA testing, the j retention rate is 83% relative to the initial value. The excellent performance of the as-prepared sample is mainly due the strong electron interaction between Cr and Ni atoms, which is conducive to the formation of Ni³⁺, its mesoporous structure, which is helpful for electron transport and electrolyte diffusion, and its amorphous structure, which provides more UOR active sites.