Urea-oxidation-assisted electrochemical water splitting for hydrogen production on a bifunctional heterostructure transition metal phosphides combining metal–organic frameworks

• Published in: Journal of colloid and interface science 2022-12, Vol.628, p.1008-1018
• Main Authors: Chen, Chunchao, Jin, Liujun, Hu, Lei, Zhang, Tingyu, He, Jinghui, Gu, Peiyang, Xu, Qingfeng, Lu, Jianmei
• Format: Article
• Language: English
• Subjects: Bifunctional catalyst; Cobalt phosphide; Hydrogen evolution reaction; Metal-organic framework; Urea electrolysis
• ISSN: 0021-9797; 1095-7103
• DOI: 10.1016/j.jcis.2022.08.127

[Display omitted] Electrocatalyzed urea-assisted wastewater splitting is a promising approach for sustainable hydrogen production. However, the lack of cost-efficient electrocatalysts hinders its practical application. Herein, bimetal phosphide (NiCoPx) nanowire arrays decorated with ultrathin NiFeCo metal–organic framework (NiFeCo-MOF) nanosheets on porous nickel foam (NF) were designed for urea-assisted wastewater splitting. The core–shell NiCoPx@NiFeCo-MOF hybrids were prepared via successive hydrothermal, gas-phase phosphorization and hydrothermal strategies. Encouragingly, the novel NiCoPx@NiFeCo-MOF/NF electrode served as an excellent bifunctional electrocatalyst for both the cathodic hydrogen evolution reaction (HER) and the anodic urea oxidation reaction (UOR) in urea-assisted water splitting, which merely required an overpotential of 44 mV to deliver a current density of 10 mA cm−2 for HER and a voltage of 1.37 V to deliver a current density of 100 mA cm−2 for UOR in 1.0 M KOH + 0.5 M urea. Benefiting from the highly exposed electroactive sites in exquisite three-dimensional (3D) hierarchical structure, multicomponent synergistic effect, accelerated electron transfer, easy electrolyte access and diffusion of released gas bubbles, the as-fabricated NiCoPx@NiFeCo-MOF/NF exhibited outstanding electrocatalytic performance. The mechanism of water splitting was elucidated by density functional theory calculations. Interestingly, NiFeCo-MOF possessed optimized COO* adsorption ability on Ni sites that were beneficial to UOR intermediates. More significantly, this work paves the way for the design and fabrication of bifunctional electrocatalysts for urea-containing wastewater treatment and sustainable hydrogen production.