NiCoP/Co₃O₄ composite electrocatalyst with p-n heterojunction promotes urea oxidation in direct urea fuel cells

Direct urea fuel cells (DUFCs) have great potential in recovering chemical energy from wastewater containing urea. The efficiency of the urea oxidation reaction (UOR) on the anode of a DUFC has a significant influence on its power output. Currently, the development of UOR catalysts with high catalytic activity and durability remains extremely challenging. To address this, the 3D nanoflower-like NiCoP/Co₃O₄ composite was prepared by coupling n-type NiCoP with p-type Co₃O₄ in-situ grown on nickel foam (NF). The NiCoP/Co₃O₄-NF composite can form a strong built-in electric field at the interface to reconstruct the electronic structure, greatly reducing the activation energy of the UOR process. The NiCoP/Co₃O₄-NF composite with superlative UOR catalytic capacity can break through 100 mA cm^-2 at only 1.34 V and remain stable for 120 h at 10 mA cm^-2. Furthermore, the NiCoP/Co₃O₄-NF composite also demonstrates hydrogen evolution reaction (HER) performance with a potential of 226.04 mV at 100 mA cm^-2 and remains stable for 100 h at 10 mA cm^-2. Density functional theory (DFT) calculations show that the adsorption strength of NiCoP/Co₃O₄-NF on the reaction intermediates is moderate, which is advantageous for the reaction. The DUFC, with the NiCoP/Co₃O₄-NF composite electrode as the anode (DUFC@NiCoP/Co₃O₄-NF), can reach a power density of 20.16 mW cm^-2. Even when using human urine as fuel, the power of the DUFC@NiCoP/Co₃O₄-NF can reach 14.17 mW cm^-2. This study provides a new proposition for the design of p-n heterojunction catalysts for efficient urea-assisted hydrogen production and urea decomposition for power generation.