Thermodynamic aspects of urea oxidation reaction in the context of hydrogen production by electrolysis

This work reports the revisited thermodynamic parameters of urea oxidation reaction CO(NH2)2+H2O→N2+3H2+CO2, which is used in the urea-assisted electrolytic cell for the electrochemical production of hydrogen. It has been repeatedly stated in the literature that the open-circuit voltage for this reaction is equal to 0.37 V, which is significantly less than in the case of hydrogen evolution with a coupled oxygen evolution reaction (1.23 V at 298 K). This feature is considered as a very important advantage of urea-assisted systems. Our calculations showed that the value of 0.37 V is erroneous, and the correct value of the open-circuit voltage is ∼0.07 V. The specified thermodynamic parameters confirm the excellent prospects of electrochemical hydrogen production with the coupled reaction of urea oxidation and indicate wide potential opportunities for further reduction of energy consumption in the electrolysis process.