Mass Transport Limitations of Water Evaporation in Polymer Electrolyte Fuel Cell Gas Diffusion Layers

Abstract

Facilitating the proper handling of water is one of the main challenges to overcome when trying to improve fuel cell performance. Specifically, enhanced removal of liquid water from the porous gas diffusion layers (GDLs) holds a lot of potential, but has proven to be non-trivial. A main contributor to this removal process is the gaseous transport of water following evaporation inside the GDL or catalyst layer domain. Vapor transport is desired over liquid removal, as the liquid water takes up pore space otherwise available for reactant gas supply to the catalytically active sites and opens up the possibility to remove the waste heat of the cell by evaporative cooling concepts. To better understand evaporative water removal from fuel cells and facilitate the evaporative cooling concept developed at the Paul Scherrer Institute, the effect of gas speed (0.5–10 m/s), temperature (30–60 °C), and evaporation domain (0.8–10 mm) on the evaporation rate of water from a GDL (TGP-H-120, 10 wt% PTFE) has been investigated using an ex situ approach, combined with X-ray tomographic microscopy. An along-the-channel model showed good agreement with the measured values and was used to extrapolate the differential approach to larger domains and to investigate parameter variations that were not covered experimentally.

Discrete-Particle Model to Optimize Operational Conditions of Proton-Exchange Membrane Fuel-Cell Gas Channels

“…Therefore, the single-phase region shown in experiments , is represented by droplet regimes. If phase change was included, there will be a distribution of evaporation rates along the channel, as shown by experiments and modeling, which should be considered in the next iteration of the model. Condensation effects may cause the distribution of injection points to move toward the side walls because water clusters under the rib regions will wick on the channel side walls, which was shown in X-ray imaging studies .…”

Fault Structural Analysis Applied to Proton Exchange Membrane Fuel Cell Water Management Issues

“…C3 : P H2Oca ≤ P sat (24) Then as depicted in [28], there is a thermodynamic equilibrium between the GdL [29] water content (λ GdL ) and the membrane water content λ m ( [30]). The constraint C4 represents this equilibrium.…”

A model based investigation of evaporative cooling for polymer electrolyte fuel cells – Stack level analysis

“…Additionally, the evaporation of water in fuel cell GDLs has been studied extensively, both, numerically [38][39][40][41] and experimentally [40,[42][43][44] by several groups.…”