Reactive sensor for investigation of gas diffusion layer hydrophobicity in PEM fuel cells

In an effort to develop methods for spatial characterization of the active interface (catalyst/polymer electrolyte/carbon fiber) in polymer electrolyte membrane fuel cell (PEMFC) gas diffusion electrodes, the present work investigates the effect of the hydrophobic agent [0-20 wt % Teflon poly(tetrafluoroethylene) (PTFE)] and Nafion loading on the properties of the carbon fiber gas diffusion layer (GDL). The reduction of O-2 in 0.1 M H2SO4 on various uncatalyzed carbon fiber papers (two-electron process) was chosen as the additive-sensitive electrochemical reaction. The oxygen electro-reduction on the carbon fiber paper was a strong function of PTFE and Nafion content, as revealed by both cyclic voltammetry and electrochemical impedance spectroscopy. The changes in charge-transfer resistance can be used as a quantitative measure of both PTFE and Nafion content. The addition of PTFE increased while the presence of Nafion decreased, in a sensitive fashion, the charge-transfer resistance of the two-electron O-2 reduction as determined by impedance spectroscopy. Hence, oxygen electroreduction could be used as an electrochemical "sensor" for the nondestructive analysis of the GDL properties. The electrochemical studies were corroborated by cross-sectional scanning electron microscopy and mercury intrusion porosimetry investigation of PTFE penetration in the carbon fiber paper.