Experimental and Analytical Study of Gas Diffusion Layer Materials for Ribbon Fuel Cells

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 $0.39Ω/sq$⁠, whereas the new diffusion materials exhibited in-plane resistances in the range of $0.18−0.06Ω/sq$⁠. 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 $0.28A/cm2$ and $0.48A/cm2$ 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.