Electrochemical CO2 reduction at copper electrodes with enhanced long-term stability by pulsed electrolysis

Titelangaben

Engelbrecht, Andreas ; Uhlig, Conrad ; Stark, Oliver ; Hämmerle, Martin ; Schmid, Günter ; Magori, Erhard ; Wiesner-Fleischer, Kerstin ; Fleischer, Maximilian ; Moos, Ralf:
Electrochemical CO2 reduction at copper electrodes with enhanced long-term stability by pulsed electrolysis.
2018
Veranstaltung: Electrochemistry 2018 , 24.-26.09.2018 , Ulm, Germany.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Poster )

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Abstract

CO2 can be electrochemically reduced to value-added products such as CH4 and C2H4. This research was pioneered by the work of Hori et al. in the 1980’s and has found renewed in-terest in the past few years. Copper catalysts are known for their selectivity to reduce CO2 to hydrocarbons, however, they show a lack of long-term stability. The underlying mechanism is still under discussion. It has been shown in the past that a pulsed operation of the electro-lyser has a positive effect on the long-term stability. We performed pulsed electrolysis with copper sheet electrodes in a divided H-cell and system-atically investigated the influence of different rectangular pulse sequences on the formation of gaseous products of CO2 reduction (CO, CH4, C2H4, H2). The variation of the pulse sequence comprised the following parameter range: a) the cathodic voltage level was var-ied between -1.5 V ... -1.8 V, b) the ratio of the duration of the anodic and the cathodic steps was varied in the range from 5 s:5 s to 5 s:500 s, and c) the anodic voltage level was varied between +0.15 V … -0.88 V. The electrolyte was a 0.1 M KHCO3 solution. The total electrolysis time in each experiment was 16 h. Depending on the pulse sequence, the composition of the product gas changes, and maximum Faraday efficiencies (FE, quotient of the charge needed for the formation of a product and the total charge introduced) of approx. 50% for CH4, approx. 30% for C2H4 and approx. 25% for CO are achieved, respectively. At the same time, the formation of H2 (HER) can be reproducibly suppressed to approx. 10% FE. During electrolysis, various rearrangement processes take place on the surface of the electrodes, which range from a preservation of the original morphol-ogy, through rearrangement of the morphology, to sheet corrosion. By choosing appropriate operating conditions it is possible to achieve a positive influence on the long-term stability of the process and simultaneously to avoid unwanted corrosion of the electrode.