Influence of compressive stress on the pore structure of carbon cloth based gas diffusion layer investigated by capillary flow porometry

A promising type of proton exchange membrane fuel cell (PEMFC) architecture, the ribbon fuel cell, relies on the gas diffusion layer (GDL) to conduct electrical current in-plane to adjacent cells or collector terminals. The potential advantages of the fuel cell ribbon architecture with respect to conventional fuel cell stacks include reduced manufacturing costs, reduced weight, reduced volume, and reduced component cost. This work addresses the critical component of fuel cell ribbon assemblies, which is the GDL. The materials and treatments necessary to fabricate GDLs for fuel cell ribbon assemblies are presented along with experimental results for various candidate gas diffusion materials. An experimentally validated analytical model, which focuses on the electrical losses within the GDL of the ribbon fuel cell, was developed and used to guide design and testing. Low in-plane resistance is extremely important for the ribbon architecture because high in-plane GDL resistance can cause significant variation in current density over the catalyzed area. To reduce the current variation the new GDLs are fabricated with materials that have reduced in-plane resistance. Properties and performance for a common gas diffusion media, ELAT® LT-1200W (BASF Fuel Cell), were measured as a reference for the new gas diffusion layers. The widely used ELAT material exhibited an in-plane resistance of 0.39 Ω/sq, whereas the new diffusion materials exhibited in-plane resistances in the range of 0.18−0.06 Ω/sq. The performance of a ribbon fuel cell was predicted using a two-dimensional model that combines the polarization curve for a conventional bipolar plate type PEMFC and the resistive properties of the GDL material of interest. Experiments were performed to validate the analytical model and to prove the feasibility of the ribbon fuel cell concept. Results show that when the novel GDLs were adhered to a catalyzed membrane and tested in a ribbon fuel cell test assembly utilizing serpentine flow channels and in-plane current collection, a range of performance was achieved between 0.28 A/cm2 and 0.48 A/cm2 at a cell potential of 0.5 V. The agreement between the experimental data and the model predictions was very good for the ELAT and the B1/B polyacrylonitrile (PAN)-based carbon cloth. Differences between predicted and measured performance for a pitch-based GDL material were more significant and likely due to mass transport limitations.

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A Study on the Evaluation of Effective Properties of Randomly Distributed Gas Diffusion Layer (GDL) Tissues with Different Compression Ratios

Applied Sciences ◽

10.3390/app10217407 ◽

2020 ◽

Vol 10 (21) ◽

pp. 7407

Author(s):

Haksung Lee ◽

Chan-Woong Choi ◽

Ki-Weon Kang ◽

Ji-Won Jin

Keyword(s):

Fuel Cell ◽

Carbon Fiber ◽

Diffusion Layer ◽

Effective Properties ◽

Compressive Load ◽

Gas Diffusion Layer ◽

Gas Diffusion ◽

Fiber Content ◽

Equivalent Material ◽

Carbon Cloth

The gas diffusion layer (GDL) typically consists of a thin layer of carbon fiber paper, carbon cloth or nonwoven and has numerous pores. The GDL plays an important role that determines the performance of the fuel cell. It is a medium through which hydrogen and oxygen are transferred and serves as a passage through which water, generated by the electrochemical reaction, is discharged. The GDL tissue undergoes a compressive loading during the stacking process. This leads to changes in fiber content, porosity and resin content due to compressive load, which affects the mechanical, chemical and electrical properties of the GDL and ultimately determines fuel cell performance. In this study, the geometry of a GDL was modeled according to the compression ratios (10%, 20%, 30%, 40% and 50%), which simulated the compression during the stacking process and predicted the equivalent properties according to the change of GDL carbon fiber content, matrix content and pore porosity, etc. The proposed method to predict the equivalent material properties can not only consider the stacking direction of the material during stack assembling process, but can also provide a manufacturing standard for fastening compressive load for GDL.

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