Investigation of urea oxidation as a potential anode reaction during CO2 electrolysis

The electrooxidation of urea was investigated on Ni90Fe10 electrodeposited films as an alternative reaction to the oxygen evolution reaction (OER) during CO2 electrolysis. The results show an excellent activity, 135 mA cm(geo)(-2) (by cyclic voltammetry) and stability (90-76.5 mA cm(geo)(-2)) over 30 min in alkaline media (NaOH 1 M + 0.25 M urea). The activity was extremely pH dependent, decreasing sharply at pH 12-13, but remaining higher than the OER at all pH investigated. The activity could be recovered by replacing the electrolyte by a fresh solution. The absence of correlation between the amount of NiOOH sites formed and the current measured at different pH suggests a limitation, either kinetic in the formation of NiOOH or in the amount of hydroxyl anions available, at pH < 14. Nevertheless, at pH approximate to 14, chronopotentiometry measurements revealed a gain of 120 mV in the potential needed to achieve a current density of 50 mA cm(geo)(-2). Meanwhile, the production of formate at a tin cathode remained constant or slightly increased in the presence of urea at the anode at all potentials tested.