Systematic Analysis of Electrochemical CO₂ Reduction with Various Reaction Parameters using Combinatorial Reactors

Abstract

Applying combinatorial technology to electrochemical CO2 reduction offers a broad range of possibilities for optimizing the reaction conditions. In this work, the CO2 pressure, stirring speed, and reaction temperature were varied to investigate the effect on the rate of CO2 supply to copper electrode and the associated effects on reaction products, including CH4. Experiments were performed in a 0.5 M KCl solution using a combinatorial screening reactor system consisting of eight identical, automatically controlled reactors. Increasing the CO2 pressure and stirring speed, or decreasing the temperature, steadily suppressed H2 production and increased the production of other reaction products including CH4 across a broad range of current densities. Our analysis shows that the CO2 pressure, stirring speed, and reaction temperature independently contributed to the limiting rate of CO2 supply to the electrode (Jlim). At a constant temperature, the limiting current density of CH4 increased proportionally with Jlim, illustrating that the production rate of CH4 was proportional to CO2 supply. Varying the CO2 pressure and stirring speed hardly affected the maximum Faradaic efficiency of CH4 production. However, changes to the reaction temperature showed a significant contribution to CH4 selectivity. This study highlights the importance of quantitative analysis of CO2 supply in clarifying the role of various reaction parameters and understanding more comprehensively the selectivity and reaction rate of electrochemical CO2 reduction.

System Design Rules for Intensifying the Electrochemical Reduction of CO2 to CO on Ag Nanoparticles

“…For industrial feasibility of eCO 2 RR, key parameters such as catalyst utilization (or catalyst mass activities), rates (current densities), selectivities (FEs), full cell energy efficiencies (EEs), conversion per pass of CO 2 , and performance stability need to be maximized. Prior studies in eCO 2 RR and allied fields like CO electroreduction try to maximize the above mentioned parameters using reactor engineering approaches to optimize the catalyst loading, electrolyte flow rate, electrolyte concentration, CO 2 flow rate, or use specialized cell designs, high pressures and high temperatures . Various technoeconomic studies suggest that for eCO 2 RR to CO to become economically feasible, j CO exceeding 400 mA/cm 2 with greater than 90 % FE are required at cell overpotentials less than 1.3 V, to ensure an EE exceeding 50 % .…”

Effects of temperature and gas–liquid mass transfer on the operation of small electrochemical cells for the quantitative evaluation of CO2reduction electrocatalysts

“…[29][30][31]36,37 The electrochemical cells used for the analysis of CO2R catalysts are, in fact, miniature chemical reactors in which known reaction conditions must be maintained. 38 This concept has been emphasized in the electrochemical engineering literature, [39][40][41] with a number of studies focused on gas sparged systems [42][43][44][45] similar in design to the cells described above. Notably, the dilute electrolyte conditions and corresponding mass transfer limitations typical of CO2R make the cell design implications even more important.…”

High Selectivity Towards Formate Production by Electrochemical Reduction of Carbon Dioxide at Copper–Bismuth Dendrites

“…[26] With regard to reported efficiencies and production rates in CO 2 electroreduction processes, in many cases thesev alues are the result of experiments where few parameters are being explored.Arecentstudy demonstratedthat varying the transport rate to the electrode, cell pressure,a nd temperature all result in significant (up to 50 %) changes in the distribution, selectivity and productionr ates. [27] Consequently,m ost studies represent as pread of performance values over ar ange of parameters instead of precise and specific quantities.…”