Electrochemical synthesis of urea at gas-diffusion electrodes

Simultaneous reduction of carbon dioxide and nitrite ions was investigated at gas-diffusion electrodes with various metallophthalocyanine (M–Pc, M: Cr, Mo, Mn, Ru, Co, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au, Zn, Cd, In, Tl, Sn and Pb) catalysts. The formation of urea, CO, formic acid and ammonia at the gas-diffusion electrodes with Group 8–14 catalysts, except for Al and Ge, was found in the simultaneous reduction. The maximum current efficiency of urea formation is about 40% at −1.5 V on Ni–Pc catalysts. The formation of urea at the gas-diffusion electrodes with Group 4–7 catalysts was not found in the simultaneous reduction of CO2 and nitrite. The ability for urea formation with the catalysts depends on the ability for CO and NH3 formation. The catalysts with high ability for CO and NH3 formation could form large amounts of CO-like and ammonia-like precursors.