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We report on the long-term stability of the electrochemical reduction of CO 2 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, CH 4 , C 2 H 4 , H 2 ) 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 C 2 H 4 and 20 to 50% FE for CH 4 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, CH 4 , C 2 H 4 ) was achieved.

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The electrochemical reduction reaction of CO2 (CO2RR) is a promising avenue toward the renewable energy‐driven transformation of a greenhouse gas toward fuels and value‐added chemicals. While copper uniquely can catalyze this reaction to longer carbon chains, Cu‐based electrodes continue to face numerous challenges, including low selectivity toward desired products and poor stability. To unlock its potential for large‐scale industrial implementation, great interest is shown in tackling these challenges, primarily focusing on catalyst and electrode modifications and thereby leaving a research gap in the effects of operation conditions. Herein, back pressure application is introduced in CO2 electrolyzers at industrially relevant current densities (200 mA cm−2) in order to steer selectivity toward C2+ products. The back pressure adjusts CO2 availability at the electrode surface, with a high CO2 surface coverage achieved at ΔP = 130 mbar suppressing the competing hydrogen evolving reaction for 72 h and doubling of stable ethylene production duration. Faradaic efficiency of 60% for C2+ products and overall C2+ conversion efficiency of 19.8% are achieved with the easily implementable back pressure operation mode presented in this study. It is proven to be a promising tool for product selectivity control in future upscaled Cu‐based CO2 electrolysis cells.

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