Investigation of hydrophobic treatments with perfluoropolyether derivatives of gas diffusion layers by electrochemical impedance spectroscopy in PEM-FC

Abstract

In the present work the effect of two different hydrophobic surface treatments, for gas diffusion layer (GDL) for PEM fuel cells, is reported. This hydrophobic coating consists of two new perfluoropolyether (PFPE) dispersions; the PFPE used are commercially available products (Fluorolink® P56 and Fluorolink® TLS 5007, from Solvay Solexis s.p.a., Italy). The former perfluoropolyether (P56) is an anionic, segmented polyurethane with high molecular weight, while the latter (TLS) is a phosphate ammonium salt with lower molecular weight. The GDLs obtained were tested in a single fuel cell at the lab scale. The cell testing was run at 60°C with two different relative humidities (RHs) of the feeding gases: 80/60% and 80/100%, Hydrogen/Air respectively.The new PFPE coatings guarantee good cell performances and in order to assess ohmic resistances and electrochemical parameters, AC electrochemical impedance spectroscopy (EIS) of the running cell was also performed. The EIS spectra were recorded at OCV and from low to high current density (i.e. 0.17, 0.34, 0.52, 0.7 and 0.87A/cm2).