Identification of Mass Transfer Mechanisms inside an Industrial Electrochemical Cell for CO2 to Formate Conversion through 2D Transient Modeling
Authors: Bahreini Mohammad , Desilets Martin , Pahija Ergys , Legrand Ulrich , Fink Arthur 
Published: December 2024

Since the dawn of the industrial revolution, the Earth's atmosphere has experienced a gradual increase in carbon dioxide (CO2) concentrations, leading to the trapping of solar energy and consequent global warming. This shift in climate dynamics carries significant consequences, including heightened levels of secondary pollutants in urban areas and an increase in the frequency and severity of natural disasters. To address these pressing environmental challenges, there is a widespread global inclination toward adopting sustainable technologies and reducing CO2 and other greenhouse gas emissions [1,2].
However, the primary source of CO2 emissions remain the combustion of fossil fuels, which is expected to persist as the dominant energy source for the foreseeable future. It is driven by extensive usage across various sectors, notably in the chemical industry and transportation. Despite growing awareness of the need to curb greenhouse gas emissions, transitioning to viable alternatives in these sectors presents formidable challenges. Factors such as entrenched infrastructure, economic dependencies, and technological barriers complicate the shift away from fossil fuels, highlighting the complexity of the transition toward sustainable solutions [1,3].
The emergence of CO2 electrolyzers, which can be powered by various energy sources including renewable options like solar power, can redefine the production of chemicals, reducing our reliance on fossil fuels in this sector and thereby mitigating CO2 emissions. This shift offers a promising solution to address global warming problems. These devices facilitate the conversion of CO2 into valuable chemicals through electrochemical processes, specifically the electrochemical CO2 Reduction Reaction (CO2RR), thus aiding emission reduction and integrating renewable energy into global infrastructure. However, scaling this technology to industrial levels reveals significant hurdles. Achieving consistent reaction rates across the whole cell's surface area, optimizing current distribution, and addressing challenges related to CO2 mass transfer are critical considerations. Among these challenges, maintaining electrochemical performance over time emerges as the most important factor. Industrial-scale implementation is further complicated by the inherent complexity of operational modes, expanded surface areas, and intricate flow paths. Consequently, adopting a model-based approach becomes paramount. Leveraging computational models allows for comprehensive analysis and optimization of large-scale CO2 electrolysis systems, helping to understand system dynamics and to refine pivotal components such as gas diffusion electrodes. Advancing CO2 electrolyzer technology holds significant importance for both academic research and industrial applications in the pursuit of sustainable energy solutions [4,5].
In this study, we present a two-dimensional transient-state multiphase Gas Diffusion Electrode (GDE) model, which describes mass and heat transfer, electrochemical kinetics, aqueous-phase reactions, and species concentrations within the total flowing electrolyte volume in the system over time. Our study focuses on the conversion of CO2 to formate due to its industrial significance and commercial viability. We provide experimental validation of the model using results obtained from an industrial cell, specifically the first industrial 1526 cm² electrochemical cell. This represents a significant advancement, with a 60-fold increase from the largest three-compartment electrolyzer reported to date [6]. Subsequently, we apply the model to predict the scalability of the GDE and assess the impact of key parameters on system performance. We observe that electrolyzers with greater heights exhibit significantly stronger reactions at the same current density. Moreover, the model effectively captures the pH time dependency at various points in the GDE and aids in identifying the stability and evolution of the chemical species composing the GDE. It also accurately represents variations in carbonate and bicarbonate production, as well as the decrease of hydroxide over time in the catholyte. Furthermore, in the context of stability, we numerically investigate the impact of catalyst degradation over time on system performance.
[1] Konderla, Vojtěch. "Numerical modelling of a gas diffusion-based CO2 electrolyser with flowing catholyte." (2022).
[3] Kibria, Md Golam, et al. "Electrochemical CO2 reduction into chemical feedstocks: from mechanistic electrocatalysis models to system design." Advanced Materials 31.31 (2019): 1807166.
[3] Smith, Wilson A., et al. "Pathways to industrial-scale fuel out of thin air from CO2 electrolysis." Joule 3.8 (2019): 1822-1834.
[4] Yang, Ziming, et al. "Modeling and upscaling analysis of gas diffusion electrode-based electrochemical carbon dioxide reduction systems." ACS Sustainable Chemistry & Engineering 9.1 (2020): 351-361.
[5] Gawel, A., et al., Electrochemical CO2 reduction-the macroscopic world of electrode design, reactor concepts & economic aspects. IScience, 2022.
[6] Fink, A.G., et al., Scale‐up of Electrochemical Flow Cell towards Industrial CO2 Reduction to Potassium Formate. ChemCatChem: p. e202300977.

Figure 1