Perfluoropolyethers as superhydrophobizing agents for carbon-based surfaces of fuel cell gas diffusion layers

W. Navarrini, M. Sansotera, M.V. Diamanti, MP. Pedeferri, M. Gola, G. Dotelli
Politecnico di Milano,

Keywords: superhydrophobic, perfluorinated coating, conductive


Perfluoropolyether (PFPE) peroxide has been employed in the functionalization of conductive carbon-based materials to confer them the highly hydrophobic surface properties of the perfluorinated materials. The thermal decomposition of a linear PFPE peroxide produced PFPE free-radicals that covalent1y bonded the unsaturated moieties on the surface of carbon-based materials such as carbon black (CB) and carbon cloth (CC). In particular, perfluorinated free-radicals can directly bond to the unsaturated structure of these carbonaceous materials without any spacer that decreases thermal or chemical stability of the resulting materials [1]. PFPE-functionalized materials revealed exceptional hydrophobic behavior, by showing water contact angle values over the threshold of superhydrophobicity. The relationship between the linkage of PFPE chains and the modification of surface physical-chemical properties were studied combining resistivity measurements, scanning electron microscopy (SEM) X-ray photoelectron spectroscopy (XPS), and surface area analysis with Brunauer-Emmett-Teller (BET) technique. Results on resistivity measurements were specially promising and revealed that, despite insulating nature of PFPE, functionalized carbonaceous materials retained their conductive properties [2]. The PFPE-functionalized carbonaceous materials were tested in a fuel cell as a single- and dual-layer gas diffusion layers (GDLs). The cell testing for both single- and dual-layer GDLs was run at two temperatures, 60°C and 80°C, and two relative humidities (RH) of feeding air, 80% and 60% (hydrogen feeding gas humidity was fixed at 100%). AC electrochemical impedance spectroscopy (EIS) of the cell was also performed and EIS spectra were recorded at OCV as well as from low to high current density (i.e., 0.17, 0.34, 0.52, 0.70 and 0.87 A/cm2). The experimental spectra were modelled with all in-series equivalent circuits comprising a resistance and two parallel constant phase/resistance sub-circuits.