Soto Álvaro Moreno, Lake Jack R, Varanasi Kripa K
Department of Mechanical Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02139, United States.
Langmuir. 2022 Jan 25;38(3):1020-1033. doi: 10.1021/acs.langmuir.1c02540. Epub 2022 Jan 11.
The novel use of carbon dioxide (CO) 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 CO 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 H is favored to the detriment of CO electroreduction. Therefore, the extent to which H 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 CO electroreduction and the corresponding pH evolution near the electrode's surface. For the latter, two main contributions are distinguished: gas depletion due to CO consumption and ion generation in areas close to the electrocatalyst surface. pH is then suggested as an accurate and indirect means to measure CO concentration in a liquid electrolyte. We conclude that CO 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.
利用二氧化碳（CO）电还原生成对温室效应无影响的碳基产品，这一新颖用途推动了将二氧化碳视为未来清洁燃料生产的可再生原料的愿景。根据电催化的材料选择，二氧化碳还原反应（CO2RR）有望产生多种产品。然而，由于靠近工作电极区域（相对于扩散边界层）的CO浓度在其被消耗并转化为其他产品时会降低，H的生成受到青睐，这不利于CO的电还原。因此，H的产生程度可作为评估CO2RR效率的一个指标。本文提出了一个模型，该模型考虑了气态物质在水溶液中随时间的消耗模式，以及其对长期CO电还原和电极表面附近相应pH值变化的影响。对于后者，可区分出两个主要因素：由于CO消耗导致的气态物质消耗，以及靠近电催化剂表面区域的离子生成。因此，pH值被认为是测量液体电解质中CO浓度的一种准确且间接的方法。我们得出结论，CO的消耗会导致电化学反应效率大幅下降。最后，我们讨论了几种可能延迟气态物质消耗所引起的不利影响的方法，例如利用脉冲电还原，定期对电极施加电流进行周期性通断循环。
