Synthesis of defective Ni-Mn layered double hydroxides nanosheets via alkali-assisted Mo doping for urea electro-oxidation

Urea oxidation reaction (UOR) with favorable thermodynamic potential provides a good application prospect in renewable energy infrastructure. However, the sluggish kinetics caused by 6e- transfer greatly hinders the usage of urea as fuel, efficient catalysts are urgently needed in consequence. In response, alkali-assisted Mo doped into Ni-Mn layered double hydroxides (Mo-NiMnLDH-OH) with laminate structure is synthesized via one-pot hydrothermal method. The alkali-assisted Mo doping contributes the modified morphology and microstructure, the tuned chemical states of Ni and Mn species, simultaneously generates defects and more active sites. The existence of alkali plays a vital role in promoting the Mo doping. Without alkali, the Mo doping should damage the laminate structure, and the chemical states of active sites cannot be efficiently tuned. When used as catalyst for UOR, the current density of 45.3 mA cm-2 and a specific current activity of 1132.8 mA cm-2 mg- 1 for MoNiMnLDH-OH can be achieved at the potential of 1.623 V (vs. RHE), which is 4-fold higher than that for NiMn layered double hydroxides without doping. Both indirect electrochemical and direct urea oxidation processes occur when using Mo-NiMnLDH-OH as catalyst, and the existence of Mo species will facilitate the occurrence of direct urea oxidation process. This work paves an effective way to synergistically engineer of Mo doping and defects into Ni-based layered double hydroxides for UOR.