Enhancement of the urea oxidation reaction by constructing hierarchical CoFe-PBA@S/NiFe-LDH nanoboxes with strengthened built-in electric fields

The slow kinetics of the oxygen evolution reaction (OER) present a major obstacle for efficient hydrogen production via water electrolysis. In contrast, the urea oxidation reaction (UOR), with its lower thermodynamic barrier, presents a promising alternative to OER. In this study, we designed and synthesized hierarchical CoFe- PBA@S/NiFe-LDH nanoboxes. Sulfur doping in nickel–iron layered double hydroxides (S/NiFe-LDH) introduces a weak built-in electric field (BIEF), which is further strengthened when combined with cobalt-iron Prussian blue analogue (CoFe-PBA) to form a heterojunction. This heterojunction created localized charge polarization at the interface, facilitating efficient electron transfer and reducing the adsorption energy of reaction intermediates, thereby significantly improving intrinsic catalytic activity. Under conditions of 1 M KOH and 0.33 M urea, the CoFe-PBA@S/NiFe-LDH catalyst achieved a current density of 50 mA cm⁻² at a relatively low potential of 1.321 V, accompanied by a low Tafel slope (53 mV dec⁻¹). Additionally, it maintained stability at 30 mA cm⁻² for 40 h. This work provides vital insights for the strategic design of highly effective heterojunction catalysts for the UOR.