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.