Characterization of Mass Transport Properties of Carbon Composite Microporous Layers Coated on Gas Diffusion Layers
Authors: Washington Brian , Goenaga Gabriel , Zawodzinski Thomas A. 
Published: September 2023

Gas diffusion layers (GDLs) utilized within anion-exchange membrane fuel cells (AEMFCs) serve a pivotal role in the management of aqueous and gaseous species within the electrode structure, ultimately influencing the stability and performance of these systems. Typically, in static environments with only the supply of gaseous molecules, reaction kinetics and mass transport limitations are present at the anode and cathode catalyst layers due to the lack of aqueous reactant species needed for high-output cell operation. The introduction of constantly replenishing alkaline electrolyte helps mitigate these issues leading to more stable, long-term device usage. Although these configurations help diminish losses within the system, they also expedite the phenomenon known as electrode flooding. This phenomenon has been studied extensively in proton exchange membrane (PEM) fuel cells and is a function of the accumulation of molecular water species at active sites within the catalyst layer due to poor electrode hydrophobicity and fluid management. Using carbon felt GDLs helps increase electrode surface area and structural integrity in flow-type environments, but they have substantially less electrical conductivities compared to carbon paper GDLs. Microporous layers (MPLs) enhance electrical conductivity and the surface area of electrode structures. In a previous study, we were able to show that carbon composite MPLs coated on carbon-felt GDLs lead to decreases in charge transfer resistances of cathode electrodes and increased current densities within the operating voltage window of these systems[1]. To better understand the performance increases and what correlation these increases have with mass transfer rates within the electrode, further analysis of these structures is needed. However, characterization techniques like external wettability and permeability measurements can be unreliable due to the surficial rigidity and asymmetry of carbon felt GDL materials. Herein, to continue this investigation, we present a study applying state-of-the-art methodologies, previously outlined by researchers at Case Western University, to MPL coated carbon felt GDLs to determine mass transport parameters such as internal contact angles[2] due to capillary effects and absolute permeability[3] of these electrode structures.
[1] Washington, B., Goenaga, G., & Zawodzinski, T. A. (2022, October). (Digital Presentation) Evaluating the Performance of Multi-Walled Carbon Nanotube Composite Microporous Layers Deposited on Carbon Felt Gas Diffusion Layers. In ECS Meeting Abstracts (No. 1, p. 15). IOP Publishing.
[2] Gurau, V., Bluemle, M. J., de Castro, E. S., Tsou, Y. M., Mann, J. A., & Zawodzinski, T. A. (2006). Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 1. Wettability (internal contact angle to water and surface energy of GDL fibers). Journal of Power Sources, 160(2 SPEC. ISS.), 1156–1162.
[3] Gurau, V., Bluemle, M. J., de Castro, E. S., Tsou, Y. M., Zawodzinski, T. A., & Mann, J. A. (2007). Characterization of transport properties in gas diffusion layers for proton exchange membrane fuel cells. 2. Absolute permeability. Journal of Power Sources, 165(2), 793–802.