The effect of electrolyte composition on the electroreduction of CO sub(2) to CO on Ag based gas diffusion electrodes

• Published in: Physical chemistry chemical physics : PCCP Vol. 18; no. 10; pp. 7075 - 7084
• Main Authors: Verma, Sumit, Lu, Xun, Ma, Sichao, Masel, Richard I, Kenis, Paul JA
• Format: Journal Article
• Language: English
• Published: 01.03.2016
• Subjects: Anions; Carbon capture and storage; Carbon dioxide; Carbon monoxide; Electrodes; Electrolytes; Electrowinning; Silver
• ISSN: 1463-9076; 1463-9084
• DOI: 10.1039/c5cp05665a

The electroreduction of CO sub(2) to C sub(1)-C sub(2) chemicals can be a potential strategy for utilizing CO sub(2) as a carbon feedstock. In this work, we investigate the effect of electrolytes on the electroreduction of CO sub(2) 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 KHCO sub(3)) studied here. Several fold improvements in partial current densities of CO (j sub(CO)) were observed on moving from 0.5 M to 3.0 M electrolyte solution independent of the nature of the anion. j sub(CO) values as high as 440 mA cm super(-2) with an energy efficiency (EE) of approximately 42% and 230 mA cm super(-2) with EE approximately 54% were observed when using 3.0 M KOH. Electrochemical impedance spectroscopy showed that both the charge transfer resistance (R sub(ct)) and the cell resistance (R sub(cell)) 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 super(-) (-0.13 V vs.RHE) < HCO sub(3) super(-) (-0.46 V vs.RHE) < Cl super(-) (-0.60 V vs.RHE). A decrease in R sub(ct) 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 CO sub(2)&z.rad; super(-) radical. EMIM based ionic liquids and 1 : 2 choline Cl urea based deep eutectic solvents (DESs) have been used for CO sub(2) capture but exhibit low conductivity. Here, we investigate if the addition of KCl to such solutions can improve conductivity and hence j sub(CO). Electrolytes containing KCl in combination with EMIM Cl, choline Cl, or DESs showed a two to three fold improvement in j sub(CO) in comparison to those without KCl. Using such mixtures can be a strategy for integrating the process of CO sub(2) capture with CO sub(2) conversion.