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

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. The NiO-CrO@N-C composite, which was synthesized by amorphous NiO and CrO nanoparticles anchored on an N-containing carbon matrix, presents excellent activity and stability for the electrocatalytic oxidation of urea.