Zinc ion effect on the electrochemical reduction of carbon dioxide at zinc electrode in aqueous solutions

The electrocatalytic activity of Zn metal electrode for potentiostatic electroreduction of CO2 has been studied in aqueous solutions of several potassium salts. The reduction products are CO and formate of which faradaic efficiency for formation depend on both the supporting electrolyte and electrode potential. Zn electrode dissolved before the electrolysis in the electrolyte solutions at the rate of 0.85 mu mol cm(-2) h(-1) in 0.05 mol dm(-3) K2SO4 which is 3.5 times greater than that in 0.1 mol dm-3 KHCO3 solution. For CO formation, the partial current density is proportional to the CO2 partial pressure and almost independent of pH, the Tafel slope of current-potential curve is ca. 200 mV/decade, and reaction orders are ca. 1 and 0.5 about CO2 and Zn2+ ion, respectively, in all the potassium salt solutions. On the other hand, in the case of HCOO- formation, the partial current density did not depend on the Zn2+ concentration in the electrolytes.