Understanding the Temperature Effects on CO2 Electrolysis Performance at High Current Densities

Abstract

The CO2 electrolysis driven with renewable sources is a promising alternative to mitigate greenhouse gas emissions by converting CO2 into valuable feedstocks and storing renewable electrical energy 1. Membrane electrode assemblies (MEAs) equipped with gas diffusion electrodes (GDEs) have shown great potential to overcome the current limitation of aqueous-fed systems while bringing this technology to economically-competing levels 2. In the last decade, many studies have been devoted to developing efficient catalyst materials and reactor designs; however, the effect of operating conditions such as temperature has not been thoroughly studied3. Given that the temperature affects CO2 electrolysis in a complex way (simultaneous effects on the CO2 diffusivity, solubility, the ionic conductivity of the membrane, and surface wettability of the GDE4), a systematic investigation is necessary to determine temperature influence on the product distributionIn this study, we investigate the temperature effects on CO2 electrolysis of Cu-based GDEs in an MEA-based approach in a temperature range between 25 and 80˚C, to enhance the selectivity of C2+ products and the energy efficiency while suppressing the hydrogen evolution (HER) and the degradation of the GDE and the membrane. For this investigation, a robust system for controlling and measuring the temperature of all the system components was developed, and we simultaneously set up proper guidelines to perform these electrocatalytic temperature measurements in a consistent and reproducible way.For evaluating the temperature influence on electrocatalytic performance, a series of electrochemical measurements such as linear sweep voltammetry (LSV), double-layer capacitance measurements (DLC), potentiostatic and galvanostatic experiments were performed. The obtained results provide insights into how CO2 diffusion, reaction kinetics, and CO2 mass transport vary with temperature and affect the overall performance. We observed improvement in reaction rates and a drop in cell voltages at higher temperatures due to the enhancement of membranes' ionic conductivity and water management. The experiments focused on selectivity and product crossover revealed a specific trend at temperatures above 60˚C for gas and liquid products, setting up the optimal conditions for a stable operation with higher faradaic efficiencies of carbon-based compounds.1 A. Vasileff, Y. Zheng and S. Z. Qiao, Adv. Energy Mater., 2017, 7, 1–21.2 T. Burdyny and W. A. Smith, Energy Environ. Sci., 2019, 12, 1442–1453.3 B. Endrődi, G. Bencsik, F. Darvas, R. Jones, K. Rajeshwar and C. Janáky, Prog. Energy Combust. Sci., 2017, 62, 133–154.4 A. Löwe, C. Rieg, T. Hierlemann, N. Salas, D. Kopljar, N. Wagner and E. Klemm, ChemElectroChem, 2019, 6, 4497–4506.