Evaluation of water transport in PEMFC gas diffusion layers using image analysis

Liquid water transport through the gas diffusion layer (GDL) of a proton exchange membrane fuel cell (PEMFC) was investigated through three interrelated studies utilizing the tools of image processing. First, a new framework and model for the digital generation and characterization of the microstructure of GDL materials with localized binder and polytetrafluoroethylene (PTFE) distributions were developed using 3D morphological imaging processing. The new generation technique closely mimics manufacturing processes and produces realistic 3D phase-differentiated digital microstructures in a cost- and time- effective manner. The generated distributions of hydrophobic (PTFE) and hydrophilic (carbon) regions representative of commercial GDL materials provides water transport modeling efforts with more accurate geometries to improve PEMFC water management. Second, through-plane transport in an operating PEMFC was investigated by developing and testing a transparent (visible and infrared) fuel cell. Visible observations and subsequent video processing revealed condensation of microdroplets on the GDL and implied the existence of condensation within the GDL. Temperature gradients across the cathode GDL under realistic operating conditions were obtained in a noninvasive manner using infrared imaging and subsequent image analysis. Recommendations for improving accuracy of PEMFC temperature measurements using infrared imaging were made. The final contribution of this work was the measurement and analysis of water breakthrough dynamics across GDL materials with and without microporous layers (MPLs). Dynamic breakthrough events, or recurrent breakthroughs, were observed for all GDL material investigated indicating the breakdown and re-build of water paths through the GDL caused by an intermittent water drainage process from the GDL surface. GDL materials without an MPL exhibited a dynamic breakthrough location phenomenon and significantly elevated water saturations. The results suggest that the MPL not only limits the number of water entries into the GDL substrate but also stabilizes the water paths. These dynamic breakthrough events were explained in terms a Haines jump transport mechanism. The main contributions of this work are: (1) Development of a new digital GDL microstructure generation algorithm, (2) Evaluation of infrared temperature measurements in the through-plane direction of a PEMFC, and (3) Identification of a new water transport mechanism in GDL materials