Hydrogen Production from Urea Sewage on NiFe-Based Porous Electrocatalysts

Development of emerging technologies for the harmless treatment and resource utilization of sewage is an urgent demand for both environment and energy concerns. This work presents the enhanced electrochemical hydrogen generation process from urea sewage by coupling the urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) under the catalysis of nanoporous nickel–iron (NP-NiFe)-based catalysts. The porous structure at the nanoscale facilitates electrocatalysis through exposure and access more active sites as well as improving the mass transfer. The optimized NP-NiFe (NP-Ni0.7Fe0.3) displays excellent oxygen evolution reaction (OER) activity. The overpotential can be further lowered to ∼60 mV at 10 mA cm–2 in urea sewage (0.33 M urea and 1 M KOH) because of coupling with the UOR, and therefore, the full water splitting potential is much lower in urea sewage (1.55 vs 1.68 V) at 10 mA cm–2. The relationship between the UOR and OER at different potentials during electrolysis of urea was further investigated by mass spectrometry. The spontaneous desorption of CO2 (UOR product) from the surface of NP-NiFe indicates that NP-NiFe has more effective UOR activity. In addition, NP-NiFe has also been proven to be used in the full electrolysis of urea-containing wastewater for hydrogen production.