Superior electrocatalytic performance of nitrogen-doped carbon-embedded Ni/NiO/NiB nanocrystals for urea oxidation†

The electrocatalytic urea oxidation reaction (UOR) can serve as an alternative to the anodic oxygen evolution reaction (OER) in water splitting. Therefore, it is of great significance to develop efficient and cheap electrocatalysts to improve the kinetics of the UOR. In this study, a Ni/NiO/NiB@NC-500 composite was prepared by anchoring Ni/NiO/NiB nanoparticles on a nitrogen-doped carbon substrate through a straightforward hydrothermal-pyrolysis method. The optimal Ni/NiO/NiB@NC-500 composite exhibited remarkable activity and stability for the UOR, that is, the current density (j) of Ni/NiO/NiB@NC-500 for the UOR was 264 mA cm⁻² at a potential of 1.67 V. Furthermore, the j retention rate of Ni/NiO/NiB@NC-500 was 84.6% of the initial value after 12 h of chronoamperometry (CA) test. The remarkable performance of Ni/NiO/NiB@NC-500 was ascribed to the following aspects: its hydrophilicity facilitated the adsorption of reactants and products, its porous spongy structure exposed more active sites for the UOR and promoted charge transfer and electrolyte diffusion, and the nitrogen-containing carbon matrix enhanced its electrical conductivity and stability. In addition, the density functional theory (DFT) calculations indicated that the introduction of B significantly reduced the energy barrier of the rate-determining step (RDS) during the UOR.