Engineering Gas Diffusion Electrode Microstructures for the Electrochemical Reduction of CO2

Abstract

The electrochemical reduction of CO2 has the potential to enable a circular economy where the captured CO2 can be utilized to produce valuable chemicals. However, existing CO2 reduction electrolyzers suffer from limited performance (i.e. low current densities) and short operation times (1-200 hours)1. The gas diffusion electrode (GDE) is a key component which determines system durability and enables higher current density operation. Yet, commercially available GDEs are carbon fiber-based materials, which were developed to fulfill the requirements of polymer electrolyte fuel cells and were repurposed for emerging CO2 electrolyzers. While functional, the commercial GDEs microstructure and surface properties do not meet the requirements of CO2 electrolysis flow cells which leads to their failure within short operation hours. These GDEs fail due to flooding through different mechanisms such as electrowetting2, capillary imbibition3, salt precipitation3, and uneven pressure distribution4. Therefore, there is a need to develop novel GDEs with engineered microstructures and wettability for the unique challenges of CO2 electrolyzers.In this research, we aim to understand the influence of the GDE microstructure on the durability and performance of CO2 electrolyzers. Instead of leveraging commercially available carbon-fiber based substrates, we conceptualize and deploy a scalable technique to manufacture novel GDEs with tunable microstructure. We hypothesize that tackling the multiphase transport challenges in CO2 electrolyzers requires electrode formats containing a plurality of pore sizes and highly controlled microstructures. Thus, we aim to develop a synthetic methodology affording a high degree of microstructural versatility and low manufacturing costs. We investigate the effect of synthetic parameters on the resulting microstructural (e.g. porosity, pore size distribution) and wetting properties. Furthermore, we aim to correlate the synthetic parameters with the resulting GDE properties (e.g. microstructure, porosity) and the corresponding transport properties (e.g. permeability, capillarity, diffusivity). These properties will be further correlated to the flow cell durability and performance. We hypothesize that tuning the pore size distribution and surface chemistry of the GDEs can enhance mass transport rates and resistance to flooding, which could enable longer operating times and higher current density. References D. Wakerley et al., Nat Energy, 7, 130–143 (2022).K. Yang, R. Kas, W. A. Smith, and T. Burdyny, ACS Energy Lett, 6, 33–40 (2021).M. E. Leonard, L. E. Clarke, A. Forner‐Cuenca, S. M. Brown, and F. R. Brushett, ChemSusChem, 13, 400–411 (2020).L. M. Baumgartner, C. I. Koopman, A. Forner-Cuenca, and D. A. Vermaas, ACS Sustain Chem Eng, 10, 4683–4693 (2022).