Two-dimensional nickel hydroxide nanosheets with high-content of nickel(III) species towards superior urea electro-oxidation

Abstract Development of high-efficient and stable electrocatalysts for urea oxidation reaction (UOR) is of a great challenge due to the sluggish kinetics of 6 e − transfer process. Here, we have developed a facile and easy-to-scale approach to fabricate two-dimensional Ni(III)-rich Ni(OH) 2 nanosheets on amine-functionalized carbon (Ni 3+ -rich Ni(OH) 2 /C-NH 2 ). Morphological characterizations confirm the existence of nanosheets, and XPS spectra indicate that the content of Ni 3+ species in Ni 3+ -rich Ni(OH) 2 /C-NH 2 (ca. 57.6%) is significantly higher than that of in Ni(OH) 2 /C-NH 2 (ca. 43.1%) and Ni(OH) 2 /C (ca. 20.7%). Electrochemical analyses illustrate that the as-prepared Ni 3+ -rich Ni(OH) 2 /C-NH 2 catalyst exhibits the highest current density (91.72 mA cm −2 ) at a potential of 0.61 V, which is 2.06-, 2.08- and 3.47-fold higher than that of Ni(OH) 2 /C-NH 2 , Ni(OH) 2 /C and Pt/C, respectively. Moreover, the Ni 3+ -rich Ni(OH) 2 /C-NH 2 catalyst also demonstrates an outstanding voltammetric cycles and long-term chronoamperometric stability. The superior electrocatalytic activity and stability could be ascribed to the synergistic effect of Ni 3+ doping as well as the amine-functionalized carbon, where higher concentration Ni 3+ species in Ni(OH) 2 sheets could provide more active sites for adsorption and transformation of urea molecules, while fluffy C-NH 2 support could enhance the ability of solute diffusion, electron transport and gas emissions, thereby dramatically improve the catalytic activity.