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

• Published in: International journal of hydrogen energy 2024-04, Vol.62, p.71-80
• Main Authors: Deng, Zeting, Du, Xiangbowen, Qian, Kaicheng, Du, Leilei, Fang, Zheng, Zhu, Jiayang, Hong, Jia, Wang, Feng, Li, Tongtong, Wei, Tong, Li, Renhong
• Format: Article
• Language: English
• Subjects: Bifunctional water splitting; Heterostructure; Hydrogen production; Nanoflower; Urea oxidation reaction
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2024.03.022

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. Using hydrothermal and calcination techniques, high-performance MoO2–NiO/NF nanoflower-like heterostructures for bifunctional urea-assisted water splitting are created. In the HER||UOR two-electrode system, the MoO2–NiO/NF heterostructure only required 1.32 V at 10 mA cm−2, which is about 261 mV smaller than that of the traditional water electrolysis. [Display omitted] •Heterostructured nanoflower-like MoO2–NiO/NF electrocatalyst is synthesized.•MoO2–NiO/NF shows superb activity and stability in urea-assisted water splitting.•The bifunctional catalyst exhibits enhanced electrocatalytic HER/UOR performance.•Heterointerface has fast electron transfer and high electrical conductivity.•Mo and Ni sites are selective for the adsorption of urea and H2O molecules.