(B,P,Co,Fe)-Ni modified on nanowood for boosting seawater urea electro-oxidation†

Coupling the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) in seawater is desirable to produce sustainable and green hydrogen due to the reduced energy consumption. However, developing high-performance UOR/HER electrocatalysts in seawater instead of pure water remains a great challenge. Herein, (B,P,Co,Fe)-Ni anchored on Paulownia Wood (PW) is proposed to enhance the overall urea-(sea)water splitting performance. The resulting sample only needs a potential of 1.34 V to deliver a large current density of 100 mA cm⁻² for alkaline UOR and features a remarkable durability to maintain 100 mA cm⁻² for 100 h. The HER and UOR (HER||UOR) coupled system in alkaline seawater-urea electrolyte for producing H₂ demonstrated a more significantly reduced electrolyzer voltage of 1.67 V obtained at 100 mA cm⁻² in comparison to that of the HER||OER system (1.98 V). The well-aligned micro-channels and nanopores in wood frameworks not only improve the hydrophilicity and aerophobicity of the whole electrode, which is conducive to the penetration of the electrolyte and release of bubbles, but also shorten the transmission distance of ions and intermediates to accelerate the reaction kinetic process. Density functional theory calculations reveal that Co, Fe, P and B co-doping in Ni effectively adjusts the electronic structure, and the adsorption/desorption behavior of the urea reaction intermediates is regulated by the synergistic effect from multiple components, resulting in an excellent catalytic activity in seawater-urea media. This work promotes a better understanding of the surface electronic structure modulation of nanowood via doping strategy and offers great potential in the design of advanced UOR/HER catalysts for hydrogen production and urea wastewater treatment.