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 at a relatively low potential of 1.321 V, accompanied by a low Tafel slope (53 mV dec). Additionally, it maintained stability at 30 mA cm for 40 h. This work provides vital insights for the strategic design of highly effective heterojunction catalysts for the UOR.