Effects of Impurities on Pre-Doped and Post-Doped Membranes for High Temperature PEM Fuel Cell Stacks

In this paper, we experimentally investigated two high temperature polymer electrolyte membrane fuel cell (HT-PEMFC) stacks for their response to the presence of reformate impurities in an anode gas stream. The investigation was aimed at characterizing the effects of reformate impurities at the stack level, including in humidified conditions and identifying fault features for diagnosis purposes. Two HT-PEMFC stacks of 37 cells each with active areas of 165 cm2 were used with one stack containing a pre-doped membrane with a woven gas diffusion layer (GDL) and the other containing a post-doped membrane with non-woven GDL. Polarization curves and galvanostatic electrochemical impedance spectroscopy (EIS) were used for characterization. We found that both N2 dilution and impurities in the anode feed affected mainly the charge transfer losses, especially on the anode side. We also found that humidification alleviated the poisoning effects of the impurities in the stack with pre-doped membrane electrode assemblies (MEA) and woven GDL but had detrimental effects on the stack with post-doped MEAs and non-woven GDL. We demonstrated that pure and dry hydrogen operation at the end of the tests resulted in significant recovery of the performance losses due to impurities for both stacks even after the humidified reformate operation. This implies that there was only limited acid loss during the test period of around 150 h for each stack.

Synthesis and physicochemical properties of sulfonated poly(aryl ether) PEMs containing phthalazinone and oxadiazole moieties

In this work, 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole (2F-Oz) is synthesized and successfully polymerized with 4-(4-hydroxyaryl)-phthalazin-1-one (DHPZ) through polycondensation to produce poly(ether 1,3,4-oxidiazole) containing phthalazinone units (PPEO) with intrinsic viscosity 1.54 dL g−1. A series of sulfonated poly(ether-1,3,4-oxidiazole)s (SPPEOs) with different degrees of sulfonation are prepared via postsulfonation reaction. The chemical structure of PPEO and SPPEOs was characterized through FT-IR and proton nuclear magnetic resonance, respectively. SPPEOs have excellent film-forming properties and readily dissolve in polar aprotic solvents, such as dimethyl sulfoxide, N-methyl-2-pyrrolidone (NMP), and so on. The water uptake of these SPPEO membranes with measured ion-exchange capacity of 1.13–1.61 mmol g−1 was 15.7–34.1% at 25°C and 17.9–59.8% at 60°C, and swelling ratio was 5.9–14.2% at 25°C and 6.6–18.1% at 60°C, respectively. The proton conductivity of SPPEO-1.61 is 0.045 S cm−1 at 30°C and 0.065 S cm−1 at 80°C, and the tensile strength of the SPPEO-1.61 is 48 MPa, and its elongation at break was 21%. The thermal and chemical stability of the SPPEOs is also examined.