Abstract
Electrochemical reduction of pressurized CO2 is proposed as an interesting approach to overcome the main hurdle of the CO2 electrochemical conversion in aqueous solution, its low solubility (ca. 0.033 M), and to achieve good faradaic efficiency in CO using simple sheet silver cathodes and undivided cells, thus lowering the overall costs of the process. The effect on the process of CO2 pressure (1–30 bar), current density, nature of the supporting electrolyte and other operative conditions, such as the surface of the cathode or the mixing rate, was studied to enhance the production of CO. It was shown that pressurized conditions allow to improve drastically the current efficiency of CO (CECO). Furthermore, at relatively high pressure (20 bars), the utilization of simple sheet silver cathodes and silver electrodes with high surfaces gave similar CECO. The stability of the system was monitored for 10 h; it was shown that at a relatively high pressure (15 bar) in aqueous electrolyte of KOH using a simple plate silver cathode a constant current efficiency of CO close to 70% was obtained.Graphic abstract
Highlights
Nowadays, in a world struggling to curb the global warming, electrochemical conversion of carbon dioxide could be considered one of the main strategies for both synthesis of chemicals and decrease of C O2 emissions [1,2,3]
When N 2 is replaced with C O2 at 0 rpm, the current density starts to increase significantly at a working potential close to − 1.45 V vs. SCE, showing that there is a range of potential of about 0.2 V where CO2 reduction can potentially take place with a very limited hydrogen evolution
Electrochemical conversion of C O2 to CO at silver electrodes was studied in detail using a liquid phase electrolyzer, investigating the effect of several operating parameters, including CO2 pressure (1–30 bar), nature of supporting electrolytes and current density
Summary
In a world struggling to curb the global warming, electrochemical conversion of carbon dioxide could be considered one of the main strategies for both synthesis of chemicals and decrease of C O2 emissions [1,2,3]. Dufek and co-workers [41, 45] have shown an improvement in CECO (~ 80%) and in reduction rate (~ 220 mA cm−2) with a corresponding suppression of hydrogen evolution reaction by working in K2SO4 aqueous electrolyte at an elevate pressure of about 20 bar for 1 h It has been demonstrated by Gabardo et al [46] that an increase in the performances of the process can be achieved due to the synergetic effect of very highly alkaline reaction environment (1–7 M KOH aqueous electrolyte), which decreases the overpotentials ( enhancing the energetic efficiency), and pressurized CO2 system (up to 7 bars), which inhibits the production of other C O2 reduction products ( increasing the selectivity). It was studied the stability of the CO production at relatively high pressure (15 bars) using different electrolytes for 10 h
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