Abstract:The optimization of fuel cell materials, particularly polymer membranes, for PEMFC has driven the development of methods and alternatives to achieve systems with more adequate properties to this application. The sulfonation of poly(styrene-co-allyl alcohol) (PSAA), using sulfonating agent:styrene ratios of 2:1, 1:1, 1:2, 1:4, 1:6, 1:8 and 1:10, was previously performed to obtain proton conductive polymer membranes. Most of those membranes exhibited solubility in water with increasing temperature and showed conductivity of approximately 10 -5 S cm -1. In order to optimize the PSAA properties, especially decreasing its solubility, semi-IPN (SIPN) membranes are proposed in the present study. These membranes were obtained from the diglycidyl ether of bisphenol A (DGEBA), curing reactions in presence of DDS (4,4-diaminodiphenyl sulfone) and PSAA. Different DGEBA/PSAA weight ratios were employed, varying the PSAA concentration between 9 and 50% and keeping the mass ratio of DGEBA:DDS as 1:1. The samples were characterized by FTIR and by electrochemical impedance spectroscopy. Unperturbed bands of PSAA were observed in the FTIR spectra of membranes, suggesting that chemical integrity of the polymer is maintained during the synthesis. In particular, bands involving C-C stretching (1450 cm -1 ), C=C (aromatic, ~ 3030 cm .
Semi-interpenetrating polymer network (SIPN) membranes were synthesized from polyethyleneimine (PEI) and DGEBA (diglycidyl ether of bisphenol A) and immersed in H 3 PO 4 solutions in order to obtain proton conductive membranes. The SIPN membranes were characterized by vibrational spectroscopy and thermogravimetric analysis, while the SIPN/H 3 PO 4 systems were studied by electrochemical impedance spectroscopy. Membranes retained water up to 210 o C, with thermal stability higher than 270 o C. Conductivity values were found between 10 -4 and 10 -3 Ω -1 cm -1 , increasing for a temperature range between 20 and 80 o C. Activation energy values evidenced the predominance of a vehicular mechanism of proton conduction in the systems and the overall properties of the membranes point to a promising material for application in Fuel Cells.
In the present work, sulfonated (IPN-SO3H) membranes were obtained from PEI/DGEBA interpenetrating polymer network membranes and characterized by vibrational infrared spectroscopy (FTIR), thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). The membranes exhibited thermal stability higher than 230 oC and conductivity of about 10-3 Ω-1cm-1 at 80 oC, with activation energy values indicating different proton conduction mechanisms depending on the sulfonation degree. Due to the overall properties of the IPN-SO3H membranes, they can be considered promising materials for application in PEMFC.
In the present work, Semi-interpenetrating polymer networks (SIPN) based on polyethyleneimine (PEI) were synthesized and characterized, aiming their future application in fuel cell devices. The membranes were acidified by two methods: (i) absorption of H 3 PO 4 from aqueous solutions and (ii) sulfonation, forming covalently bonded -SO 3 H. The thermal stability exhibited by the SIPN membranes, above 270 o C, is sufficient for their application in PEMFC and the membranes doped with H 3 PO 4 at 20% show higher conductivity values (of about 0.08 Ω -1 cm -1 ) than those obtained for the best sulfonated sample (10 -3 Ω -1 cm -1 ).
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