Pulsed Electroreduction of on Copper Electrodes-II

The pulsed method newly developed by the present authors was applied to electroreduction of CQ on Cu electrodes. It was found that the opt imum cathodic bias for generating CH ~ and C2H4 was-2.6 V vs. S CE, and the opt imum anodie bias for the generation of C2H ~ was slightly more anodic than that of CI-I4. Total faradaic efficiency ~qHC for the generation of CH4 and CzH ~ became a max imum at 1O°C and reached about 65%. Furthermore, ~c increased with increasing reduction t ime in strong contrast with the conventional potentiostatic electroreduction in wh ich ~c decreased drastically with the reduction t ime due to the poisoning effect of the products. It was proposed that some surface intermediate fo rmed by the interaction between COe and the thin oxide layer on a Cu electrode is finally reduced to CH ~ or C~H4, depending on the anodic reactions taking place during the anodie period. In the preceding study, we proposed a new technique for clarifying the reduction mechanism ~ and effectively reduc-ing carbon dioxides to hydrocarbons 2 by a pulsed method. In the latter, a cathodic bias (Vc) and an anodic bias (VA) are periodically changed. By changing Vc, VA, and their periods (Tc and TA), the generation ratio of hydrocarbons to hydro-gen can be changed. Another advantage of the pulsed method is that the poi-soning of the electrode activity due to the deposition of reduction products uch as graphitic arbons can be totally avoided. This is probably due to the effect of anodic bias which will keep intermediates from being transformed t