Boosting Urea Electrooxidation Activity of Ni₅P₄ by Vanadium Doping for Urea-Assisted Renewable Energy Conversion Devices

Abstract

The urea oxidation reaction (UOR), a competitive substitute for the oxygen evolution reaction (OER), holds superior potential to meet the upsurge of renewable energy conversion due to low theoretical potential while the sluggish UOR kinetics impede its practical application. In this report, for the first time, we demonstrate that the UOR activity of Ni5P4 is improved via V incorporation. The novel amorphous V-doped Ni5P4 (V10%-Ni5P4) microflower structure with optimized electronic structure was prepared by a solvothermal–phosphorization process. With V atoms involved, the V10%-Ni5P4 microflowers are assembled by much thinner, denser nanosheet units compared with the Ni5P4 counterpart, which endows it with more active sites, enhanced mass transfer, conductivity, and better wettability. The V10%-Ni5P4 microflowers exhibit outstanding UOR activity of 282 mA cm–2 at 1.6 V vs RHE with a low Tafel slope (36.1 mV dec–1). Furthermore, the urea-assisted electrolytic cell only needs 1.44 V to provide 50 mA cm–2 and the urea-assisted rechargeable Zn-Air battery (uZAB) is illustrated to have a higher open-circuit voltage of 1.43 V and possesses a lower potential gap than that Pt/Ir-based uZABs. This report sheds light on the role of vanadium in crystallization and structure optimization and lays the foundation for developing new UOR electrocatalysts.