Triggering the high catalytic activity of Ni-based catalyst for urea and urine electrolysis by adding Fe and constructing the CoFeP@Ni3S2 heterostructure

For effective hydrogen production, urea oxidation reaction (UOR) with much lower potential has been used to replace the water oxidation reaction (OER), while fulfilling the wastewater treatment. Development of bifunctional electrocatalysts is the crucial link in urea-assistant water electrolysis. Here, a novel composite consisting of the bimetallic phosphide nanosheets and porous Ni3S2 nanospheres was prepared by a hydrothermal-electrodeposition method. It proves that the NF/CoFeP@Ni3S2 electrode exhibits an outstanding performance for HER/UOR (HER overpotential is 173 mV and EUOR is 1.358 V, 100 mA cm-2). As for a two-electrode system taking NF/CoFeP@Ni3S2 as cathode and anode in urea medium, the voltage at 100 mA cm-2 is just 1.454 V. Even in human urine electrolyte, just only a slight current decrease is observed. Both in urea and urine, the voltage of NF/CoFeP@Ni3S2 remain stable during a 50-hour continuous operation. The formation of heterostructures between the bimetallic phosphides and Ni3S2, and Fe addition realize the gradual improvement in activity from the pristine CoP to CoFeP and then to the CoFeP@Ni3S2. This strategy provides a practical hetero-structured catalyst design form considering the structure properties of urea molecule for the efficient water-hydrogen conversion synchronous sewage treatment.