The effect of electrolyte composition on the electroreduction of CO₂to CO on Ag based gas diffusion electrodes

Abstract

The electroreduction of CO2 to C1-C2 chemicals can be a potential strategy for utilizing CO2 as a carbon feedstock. In this work, we investigate the effect of electrolytes on the electroreduction of CO2 to CO on Ag based gas diffusion electrodes. Electrolyte concentration was found to play a major role in the process for the electrolytes (KOH, KCl, and KHCO3) studied here. Several fold improvements in partial current densities of CO (jCO) were observed on moving from 0.5 M to 3.0 M electrolyte solution independent of the nature of the anion. jCO values as high as 440 mA cm(-2) with an energy efficiency (EE) of ≈ 42% and 230 mA cm(-2) with EE ≈ 54% were observed when using 3.0 M KOH. Electrochemical impedance spectroscopy showed that both the charge transfer resistance (Rct) and the cell resistance (Rcell) decreased on moving from a 0.5 M to a 3.0 M KOH electrolyte. Anions were found to play an important role with respect to reducing the onset potential of CO in the order OH(-) (-0.13 V vs. RHE) < HCO3(-) (-0.46 V vs. RHE) < Cl(-) (-0.60 V vs. RHE). A decrease in Rct upon increasing electrolyte concentration and the effect of anions on the cathode can be explained by an interplay of different interactions in the electrical double layer that can either stabilize or destabilize the rate limiting CO2˙(-) radical. EMIM based ionic liquids and 1 : 2 choline Cl urea based deep eutectic solvents (DESs) have been used for CO2 capture but exhibit low conductivity. Here, we investigate if the addition of KCl to such solutions can improve conductivity and hence jCO. Electrolytes containing KCl in combination with EMIM Cl, choline Cl, or DESs showed a two to three fold improvement in jCO in comparison to those without KCl. Using such mixtures can be a strategy for integrating the process of CO2 capture with CO2 conversion.

Transferring Electrochemical CO2 Reduction from Semi‐Batch into Continuous Operation Mode Using Gas Diffusion Electrodes

“…The influence of electrolyte type and its concentration has been described in a recent article which came to the same conclusion for Ag‐based GDEs and CO production 50. Therein, the increased activity is explained by the higher concentration of cations in the electrical double layer close to the electrode surface which helps stabilizing the reaction intermediate CO 2 − .…”

“…Therein, the increased activity is explained by the higher concentration of cations in the electrical double layer close to the electrode surface which helps stabilizing the reaction intermediate CO 2 − . Since the use of KOH as electrolyte was suggested to be beneficial for CO 2 reduction 47, 50, as a next step the electrolyte was changed to 1 M KOH and the experiments repeated with the results depicted in the above figures and mentioned in Tab. 1.…”

“…Indeed, both in terms of reactor voltage (conductivity: 170 mS cm −1 ) and the intrinsic activity, a further improvement could be achieved, as suggested. Although the potential‐current curve is very similar for KHCO 3 and KOH, one has to keep in mind the different pH values, resulting in varying standard potentials and, as a consequence, a substantially different overpotential‐current curve, as described in more detail including explanation in 50. Accordingly, as E 0 for KOH is more negative, −0.83 V vs. SHE for pH 13.71 compared to −0.61 V for pH 10, the corresponding overpotential for the reaction decreases from ∼ 400 to 200 mV.…”

Highly Efficient Solar‐Driven Carbon Dioxide Reduction on Molybdenum Disulfide Catalyst Using Choline Chloride‐Based Electrolyte

“…[23,24] It should be noted that the initial pH of the choline chloride/KOH (1:1 m) solution is about 13.3, which drops to 7.6 after CO 2 saturation due to the formation of bicarbonate ions as discussed, later in the computational part. We used a one-compartment cell (Section S5, Supporting Information) instead of a two-compartment cell to avoid a membrane separator between catholyte and anolyte.…”

Tuning of Silver Catalyst Mesostructure Promotes Selective Carbon Dioxide Conversion into Fuels

“…This observation is very unusual in heterogeneous electrocatalysis because it implies that accelerated mass transport serves,c ounter-intuitively,t o impede the rate of CO production under these conditions. [26][27][28][29] Irrespective of the specific mechanism of promotion, these results highlight that electrode mesostructuring is apowerful tool for promoting the specific activity of the surface for CO 2to-fuels catalysis. [10,24] Detailed mechanistic studies of Au-catalyzed CO production establish that CO 2 activation proceeds by rate limiting single electron transfer and adsorption of CO 2 rather than by concerted electron-proton transfer, [24] making the reaction largely insensitive to any changes in the local proton donor environment.…”