Heterostructured nanoflower-like MoO2–NiO/NF: A bifunctional electrocatalyst for highly efficient urea-assisted water splitting

The conventional anodic oxygen evolution reaction (OER) can be ideally replaced by the urea oxidation reaction (UOR) to achieve efficient hydrogen generation due to the superior thermodynamics. However, the UOR involves a slow 6-electron transfer dynamic, necessitating the utilization of high-performance catalysts to enhance catalytic efficiency. In this work, a bifunctional transition metal-based catalysts, namely, MoO2–NiO/NF heterostructure, is effectively synthesized using two-step hydrothermal methods and calcination. Benefiting from the heterogeneous interface, the nanoflower-like structure as well as the electron density redistribution, the MoO2–NiO/NF catalyst demonstrates remarkable durability and performance, with an overpotential of 139 mV to achieve 10 mA cm−2 for UOR. In addition, the bifunctional catalyst is used in a two-electrode electrolyzer, where a current density of 10 mA cm−2 is attained at a potential of 1.317 V, which is 261 mV smaller than that of the conventional water splitting system. Based on the density functional theory (DFT) calculations, the MoO2–NiO/NF heterostructure exhibits a higher density cloud in the vicinity of the Fermi level, revealing that it has faster electron transfer and higher electrical conductivity. Besides, the Mo sites and Ni sites are favorable for adsorption of CO(NH2)2 and H2O, respectively, which might optimize the reaction intermediates adsorption/desorption for UOR/HER, ultimately leading to the high electrocatalytic performance of MoO2–NiO/NF. This research opens a new window for the development of advanced heterojunction electrocatalysts assisted by urea electrocatalysis for cost-effective hydrogen production.