Solid–Polymer–Electrolyte Electrolysis of Urea Aqueous Solutions for Hydrogen Synthesis

Urea is one of the promising hydrogen sources due to its high energy density, safety, and abundance. In this paper, it was found that a Ni/Ti-mesh anode prepared by the electrodeposition method exhibited a high catalytic activity for electro-oxidation of urea/KOH aqueous solutions, producing H2, N2, and CO2 using the solid–polymer–electrolyte (SPE) cell with an anion exchange membrane (Sustainion X-37). Significant H2 evolution was observed with a good formation rate (260 μmol h–1 cm–2) and j (15.4 mA cm–2) with a high Faradaic efficiency (93.7%) at a 1.50 V applied voltage in an SPE one-compartment cell. Only H2 was obtained with a two-compartment SPE cell. Characterization studies using X-ray photoelectron spectroscopy, X-ray absorption fine structure, and scanning electron microscopy─energy-dispersive spectroscopy revealed that Ni(OH)2 species was the active phase for the urea oxidation at the Ni/Ti-mesh anode.