Transient Effects Caused by Gas Depletion during Carbon Dioxide Electroreduction

Abstract

The novel use of carbon dioxide (CO2) electroreduction to generate carbon-based products which do not contribute to the greenhouse effect has promoted the vision of carbon dioxide as a renewable feedstock for future clean fuel production. Depending on the material choice for the electrocatalysis, a certain variety of products is expected from the carbon dioxide reduction reaction (CO2RR). However, as the CO2 concentration in areas close to the working electrode (relative to the diffusive boundary layer) decreases as it is being consumed and transformed into other products, the generation of H2 is favored to the detriment of CO2 electroreduction. Therefore, the extent to which H2 is produced can be used as a metric to evaluate the efficiency of CO2RR. This article proposes a model that accounts for the modes in which aqueous gas depletion evolves over time and affects the long-term CO2 electroreduction and the corresponding pH evolution near the electrode’s surface. For the latter, two main contributions are distinguished: gas depletion due to CO2 consumption and ion generation in areas close to the electrocatalyst surface. pH is then suggested as an accurate and indirect means to measure CO2 concentration in a liquid electrolyte. We conclude that CO2 depletion causes a strong decay in the electrochemical reaction efficiency. In the end, we discuss several methods which may delay the onset of the adverse effects caused by gas depletion, such as the utilization of pulsed electroreduction, cycling the applied current to electrodes on and off periodically.

Efficient electrochemical CO2 conversion by cobalt-based metal organic frameworks modified by bimetallic gold–silver nanostructures

“…Chronoamperometry (CA) was also employed (Table S1†). The potential was calculated and reported with respect to the reversible hydrogen electrode (RHE), using the following equation: 25 E vs. RHE = E vs. Ag/AgCl + 0.0591 × pH + 0.197 VAnalysis of the collected gases was performed by a gas chromatograph (GC) equipped with a capillary column coupled with a thermal conductivity detector (TCD) for H 2 and CO detection, respectively. The Faradaic efficiency (FE i ) (i = CO, H 2 ) was determined by: 4 where n i is the mole of the product obtained from GC analysis, z i the consumed electrons for each product (2 for both CO and H 2 ), F the Faraday's constant (96 485 °C mol −1 ), and Q the charge calculated from the CA experiments during the electrochemical measurement.…”

“…Chronoamperometry (CA) was also employed (Table S1 †). The potential was calculated and reported with respect to the reversible hydrogen electrode (RHE), using the following equation: 25 E vs. RHE = E vs. Ag/AgCl + 0.0591 × pH + 0.197 V (1)…”

“…3e shows that Au-Ag@ZIF-67/GCE had better selectivity than Ag@ZiF-67/GCE. The selectivity was slightly better for Au-Ag@ZIF-67/GCE than for Au@ZIF-67/GCE, suggesting that the presence of Au NPs on the Co-based catalyst promoted CO 2 RR through reaction with COO + free radicals to form CO. 25 Fig. 3e and f show the effect of applied potential on the Faradaic efficiency of CO production (FE CO ) and H 2 evolution (FE H 2 ), respectively.…”

A robust and high performance copper silicide catalyst for electrochemical CO2 reduction

“…9,10 The lack of CO 2 in catalytic active sites of electrocatalysts leads to an increase in parasitic side reactions, especially the hydrogen evolution reaction (HER). 11…”

Effect of CO 2 shortage on the Performance of Membrane Electrode CO 2 Electrolyzer

“…When the cathode side is short of gas, the pressure difference between the two sides of the membrane electrode assembly (MEA) is too large, so that the membrane will bear a large side force and its life will be affected. For the CO 2 electrolyzer, Álvaro Moreno Soto et al [27] explored the transient effects caused by gas depletion in the process of CO 2 electric reduction by using the H-cell electrolyzer, and came to the conclusion that CO 2 consumption would lead to a strong attenuation of electrochemical reaction e ciency. Nonetheless, the process of CO 2 shortage in membrane electrode CO 2 electrolyzer has not been revealed.…”