Synergistic Effect between Co₂P/Fe₂P Nanoparticles and NiFe Layered Double Hydroxides Promotes Urea Oxidation Reaction-Assisted Hydrogen Production

Urea oxidation reaction (UOR) can replace the anode oxygen evolution reaction (OER) of overall water splitting. Compared with the OER, UOR has a lower overpotential and can significantly reduce the energy consumption of hydrogen production through water electrolysis, thus receiving widespread attention. Here, we use Co–Fe Prussian blue analogue/nickel foam (Co–Fe PBA/NF) as a precursor, and the Co–Fe PBA precursors collapse by phosphating to form a carbon layer containing Co2P and Fe2P nanoparticles and cover the NF framework (Co2P/Fe2P/NF). The carbon layer provides a limiting effect for Co2P and Fe2P nanoparticles. Subsequently, Co2P/Fe2P/NF and NiFe-LDH (iron nickel double hydroxide layer) are compounded by a hydrothermal method to obtain [Co2P/Fe2P]/NiFe-LDH/NF. A strong electronic interaction occurs at the interface of Co2P/Fe2P/NF and NiFe-LDH, resulting in a strong synergistic effect. The synergistic effect enhances the conductivity of [Co2P/Fe2P]/NiFe-LDH/NF and accelerates the reaction kinetics. Besides, Co2P/Fe2P/NF and [Co2P/Fe2P]/NiFe-LDH/NF have superhydrophilic and aerophobic structures, which promote the immersion of electrolytes and the separation of bubbles. Thus, in the presence of urea, Co2P/Fe2P/NF and [Co2P/Fe2P]/NiFe-LDH/NF electrocatalysts only require 34.4 mV and 1.38 V to drive HER (hydrogen evolution reaction) and UOR current densities of 10 and 100 mA cm–2, respectively. It is worth noting that the alkaline electrolyzer containing urea (+) [Fe2P/Co2P]/NiFe-LDH/NF||Fe2P/Co2P/NF (−) requires only a potential of 1.48 V to reach a current density of 10 mA cm–2. Compared with water electrolysis, at the same current density, the potential of UOR-assisted hydrogen production is significantly reduced by 0.64 V. This work provides an avenue for the rational design of electrocatalysts.