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We report on the long-term stability of the electrochemical reduction of CO2 at copper sheet electrodes by continuously applying rectangular, pulsed voltage cycles in series. Each pulse cycle consisted of an anodic and a cathodic voltage level. The parameters of the pulse cycle were systematically modified: cathodic (−1.5...−1.8 V) and anodic voltage levels (−0.88...+0.15 V), and ratio of anodic to cathodic pulse duration (5 s:5 s...5 s:500 s). The electrolysis runs were conducted in a divided H-cell. Volatile reaction products (CO, CH4, C2H4, H2) were analyzed with a gas chromatograph in intervals of 7.3 min. We achieved fairly stable faradaic efficiencies (FE) for hydrocarbon formation in the range of 20 to 35% FE for C2H4 and 20 to 50% FE for CH4 during 16 h of electrolysis and a remarkable suppression of hydrogen evolution reaction (HER) down to 10% FE. Additionally, we show data of two long-term electrolysis runs of 85 h and 95 h duration, respectively. Even for this prolonged electrolysis times, an outstanding, fairly constant suppression of HER and a high efficiency for the formation of carbon containing gaseous products (CO, CH4, C2H4) was achieved.
Engelbrecht et al. (Mon,) studied this question.