The electrochemical synthesis of urea by simultaneous reduction of nitrite and CO2 was performed in 0.02 mol·L-1 NaNO2 and 0.2 mol·L-1 NaHCO3 aqueous solutions at 925 Ag electrode in laboratory-scale experiments.The effect of several parameters, including electrolysis potential, temperature, and CO2 pressure, on urea formation was investigated.At the temperature of 293 K,CO2 pressure of 0.7 MPa, the electrolytic potential of -0.6 V, the current efficiency of urea formation reached 37%.Under the conditions of temperature of 273 K and electrolytic potential of -1.7 V, the current efficiency reached 26% under normal ambient pressure.Based on the relationship of current efficiency and formation of CO, NH3 and urea, a tentative reaction pathway was proposed.
The electrochemical reduction of CO2 on a Pb electrode was investigated in 0.1 mol/L KOH/methanol electrolyte at different temperatures and pressures. A graphite electrode was employed as the counter electrode, and an Ag|AgCl (sat. KCl) electrode was used as the reference electrode. The Tafel plots of the products by the electrochemical reduction of CO2 showed that the formation process of HCOOH differed from that of CO and the reduction of CO2was not limited by the diffusion of CO2 in the investigated potential range. Kinetic analysis indicated that the reaction orders were 0.573 for electrochemical reduction of CO2 to CO and 0.671 for CO2 to HCOOH in the cathodic direction.
