In-situ reconstitution of Ni(III)-based active sites from vanadium doped nickel phosphide/metaphosphate for super-stable urea-assisted water electrolysis at large current densities

• Published in: Journal of colloid and interface science 2025-02, Vol.680 (Pt A), p.665-675
• Main Authors: Li, Xiaoming, Han, Binbin, Cao, Shuyi, Bai, Hongtao, Li, Jingde, Du, Xiaohang
• Format: Article
• Language: English
• Subjects: active sites; adsorption; anion-exchange membranes; carbon dioxide; catalysts; durability; electrodes; electrolysis; energy; Heterogeneous structure construction; hydrogen; hydrogen production; mass transfer; nanosheets; nickel; Oxygen evolution reaction; oxygen production; phosphides; urea; Urea assisted water electrolysis; Urea oxidation reaction; vanadium; Vanadium doping; wastewater
• ISSN: 0021-9797; 1095-7103; 1095-7103
• DOI: 10.1016/j.jcis.2024.11.025

A co-modification strategy of transition metal V doping and heterostructure construction to promote the reconfiguration of active sites is reported. It synergistically improves the adsorption of water and urea molecules, and make the catalyst deliver excellent performance in alkaline urea assisted water splitting. Meanwhile, V doping promotes the formation of PO3−, which stabilizes the in-situ generated active site of V@NiOOH, leading to excellent stability. [Display omitted] •V doping promotes formation of Ni(PO3)2/Ni2P heterojunction in phosphating process.•V doping accelerates in-situ reconstruction of active site during OER/UOR process.•Active site V@NiOOH reduces *COO adsorption energy compared to NiOOH during UOR.•V-Ni(PO3)2/Ni2P exhibits excellent OER/UOR activity and stability in AEMWE. Efficient bifunctional electrocatalysts towards oxygen evolution reaction (OER) and urea electrooxidation reaction (UOR) are urgently needed for hydrogen production from urea-containing wastewater electrolysis. The main challenge lies in the sluggish UOR kinetics and the stability of catalyst under practical high current density. Here, a vanadium doped heterostructure of Ni(PO3)2/Ni2P with shaggy nanosheet morphology was successfully synthesized. The doping of V atoms promotes the formation of Ni(PO3)2/Ni2P heterojunction in phosphating process. It is demonstrated that V-doped Ni(PO3)2/Ni2P accelerates the generation of real active site V@NiOOH in OER and UOR processes, which can also be stabilized by the PO3− ions. The in-situ formed V@NiOOH increases the adsorption energy of urea molecule, and reduces the adsorption energy of key intermediates *COO, thus facilitating the release of CO2 product from the catalyst surface. The energy barrier of *HNCON to *NCON is also reduced dramatically, promoting the kinetics of UOR. In addition, the shaggy nanosheets morphology provides large number of catalytic sites and transport channels, which are conducive to mass transfer under high current density. As a result, the V-Ni(PO3)2/Ni2P electrode based anion-exchange membrane (AEM) electrolyzer needs only 1.61 V to drive the total urea electrolysis at an industrial grade current density of 550 mA cm−2 with an outstanding durability of 700 h. This work paves the way for designing practical efficient and stable electrocatalyst for urea contained wastewater electrolysis to produce hydrogen.