Effects of Hydrophobic Treatment on Performance and Water Management of Titanium Felt GDLs in PEMFCs

Abstract

This work follows our recent study of titanium fibre felts applied as a cathode gas diffusion layer (GDL) in a proton exchange membrane fuel cell. Here, an in-house hydrophobic treatment of PTFE (0−20 wt%) is applied to these felts and the effects on cell performance, gas diffusion, and water transport are studied with comparison to conventional commercial carbon GDLs. The titanium fibre felt with a low PTFE loading of 5 wt% consistently outperformed the untreated substrate and all carbon GDLs tested across all six sets of operating conditions. This loading is shown to improve flooding resistance due to the increased hydrophobicity while not majorly reducing porosity, gas permeability, or ohmic resistance. The low loading also maintains a fraction of hydrophilic pathways within the substrate which has been shown to contribute to improved liquid water transport under wetter operating conditions. An increase in PTFE loading to 10 wt% and higher results in reduced porosity and permeability, and saturation of the internal structure of the substrate with PTFE resulting in poorer performance. Finally, the full range of treated and untreated felts are shown to exhibit a good balance between water retention, water rejection, and hydrophobicity based on oxygen transport resistance.