Electroreduction of carbon dioxide: Part II. The mechanism of reduction in aprotic solvents

The mechanism of electroreduction of carbon dioxide in aprotic solvents on mercury, lead, tin, indium and platinum is studied using the photoemission method and the method of stationary polarization curves. When comparing the data of photoemission and “dark” (polarization) measurements it was found that in the first Tafel region of the polarization curves the rate-determining step is the transfer of the second electron to (CO₂)^.?₂ anion-radicals formed as a result of the interaction of initially generated CO^.?₂ anion-radicals with adsorbed CO₂ molecules. In the second Tafel region the rate-determining step is the transfer of the first electron to an adsorbed CO₂ molecule. The peculiarities of electroreduction of carbon dioxide in aprotic solvents can be explained provided that the effect of potential on adsorption of CO₂ and anion-radicals and the effect of repulsion of negatively charged radicals are taken into account.