Our analyses, based on the proposal assumptions, seem to have an excellent agreement with experimental observations previously reported by other researchers. For example, Dinh et al. reported the high selectivity formation of CO and C2H4 using the concentrated potassium hydroxide (KOH) electrolyte. We believe this result occurs due to a scarcity of H • radicals, as low proton concentration in electrolyte hinders the formation of O=CH-O-Cu in determinative step, leading the radical (O=C • -O-Cu) predominantly undergo radical elimination and dimerization reactions. When using common aqueous electrolytes, such as KHCO3 solution, the proton concentration in the vicinity of Cu surface is reduced under constant current conditions due to proton consumption. The reaction pathway thus gradually shifts from coupling with H • radicals to radical elimination or radical dimerization. This is the possible reason that a wide range of CO2 reduction products is observed when using aqueous electrolyte.