Rapid room-temperature fabrication of ultrathin Ni(OH)2 nanoflakes with abundant edge sites for efficient urea oxidation

Abstract Ultrathin two-dimensional (2D) nanomaterials based on transition metal compounds can serve as alternative non-precious-metal electrocatalysts for urea oxidation reaction (UOR), which is vital to the development of direct urea fuel cells. Herein, we report a fast and room-temperature route to synthsize transition metal-based (Ni, Co, Mn) ultrathin 2D nanomaterials under ambient conditions. Theoretical and experimental studies demonstrate that the edges of Ni(OH)2 are more active toward both the formation of NiOOH species and the adsorption of urea molecules than the basal planes, enabling accelerated catalytic kinetics for UOR. As expected, the β-Ni(OH)2 nanoflakes manifest considerable electrocatalytic activity toward urea oxidation, reflecting 5.7 times higher current density (142.4 mA cm-2) compared to the β-Ni(OH)2 nanosheets at a potential of 0.6 V vs Ag/AgCl. This work brings great promise for the design of advanced electrode materials in the field of electrocatalysis.