Initial Development of a Method for Optical Measurement of Water Droplet Formation in the Cathode Flow Channel of a PEM Fuel Cell

Abstract

Cathode flooding in Proton Exchange Membrane (PEM) fuel cells, or the displacement of reactant gases from the catalyst layer by water formation, limits performance and durability. Water transport is not yet well understood and can vary under different operating conditions, such as temperature. Previous work performed to characterize water formation has mostly involved water visualization, using materials/construction which could alter water condensation characteristics. The objective of this work is to investigate a method to optically measure the relative size of water droplet formation in PEM fuel cell cathode gas flow channels using an unobtrusive and previously developed temperature sensor. A single-sensor mathematical model was developed which considers channel geometry, fiber diameter, and water droplet shape and size. Droplet formation involved three different possible shapes, resulting from different hydrophobic properties of channel material. Ex situ testing utilized chromium doped yttrium aluminum garnet as the chosen phosphor, applied to a carbon paper GDL. No correlation was found between the theoretical model and the experimental findings. Although signal attenuation cannot accurately predict droplet size, it is still possible to characterize water droplet formation using statistical analysis. Since a water droplet consistently produces measurable attenuation, the frequency of water droplet detection in the flow channel can be used to characterize the amount of water formation or flooding in the cathode flow channels. The work is ongoing and new methods of water droplet characterization are still being investigated.