Study On The Preparation And Property Of Proton Exchange Membrane For Fuel Cells

Proton exchange membrane fuel cells (PEMFC), due to their high efficiency and environmental friendship, have shown promise as alternative portable, automotive, and stationary power sources. One of the important components in a PEMFC is the proton exchange membrane (PEM), which serves as the electrolyte that transfers protons from the anode to the cathode and separates the fuel and oxidizer. The state-of-the art PEMs are perfluorosulfonic acid membranes such as Nafion manufactured by DuPont. These membranes showed excellent chemical stability as well as high proton conductivity. However, Nafion suffers from disadvantages, including high cost, high methanol permeability, and limited operating temperature (80℃), due to its depressed hydrated a relaxation temperature. In recent years, the increasing demands of PEMs with high performance and low cost have stimulated the intensive researches on the development of alternatives. Among them, sulfonated poly(arylene ether sulfon)s (SPAESs)were drawn the attraction because of their high proton conductivity, high chemical and thermal stabilities. While sulfonated polyimides (SPIs)were widely studied due to their good film-forming ability, excellent thermal and mechanical stability, and excellent dimensional stability in hydrated state. So. SPAES and SPI were considered as the promising alternatives for PEMFC applications. However, the SPAES with ion exchange capacity (IEC) excesses 1.80 meq/g tend to extremely swellingand lost its mechanical stability. Only the further improvement in PEMFC performance, SPAES-based membranes should be met the need for PEMFC.This dissertation focuses on the development of SPAES-based membranes by the methods including cross-linking, interpenetrating and blending.Their performances such as dimensional stability, proton conductivity and durability investigated. Based on the former study, novel sulfonated polyphenylene-b-polyimide (PSP-b-PI) block copolymers were developed and their proton conductivity, microphase and durability were also investigated.A well optimized synthetic method was developed for 3,3'-disulfonate-4,4'-difluorodiphenyl sulfone (SDFDPS) by direct sulfonated from industrial grade 4,4'-difluorodiphenyl sulfone (DFDPS) with fumic sulfuric acid. The optimized reaction condition was found as that the molar ratio of SO₃ to DFDPS is 3:1 with a reaction temperature of 110℃for 20 h. Poly (arylene ether sulfone) copolymer prepared from the synthesized SDFDPS showed a high relative viscosity.Two types of cross-linked SPAES-based membranes were successfully developed. One is named cSPAES, which were obtained from the directly compolymerization of DFDPS, 4,4-biphenol (BP), SDFDPS.and 1.3,5-trihydroxy benzene (THB), and the structure was confirmed by ¹HNMR and FTIR. Tough and flexible cSPAES membranes were obtained through solution casting method. Compare to line structure type of SPAES. cSPAES membranes showed higher dimensional stability in water especially in hot water. These membrane showed much high proton conductivity at some high IEC level(IEC=2.43 meq/g.σ//=261 mS/cm, which was 1.9 times to that of Nafion).. The other one is named pSPAESs, which were obtained via the dehydration reaction between the sulfonic acid groups and the activated hydrogen atoms of SPAES in the presence of phosphorus pentoxide. The crosslinked structure was confirmed by the insolubility in organic solvents such as DMSO, DMAc and NMP. pSPAES membranes showed greatly improved water stability. Forexample, after aging in water for 24 h at 130℃, the dimensional change in plane and thickness of pSPAES60-9 were just 0.41 and 0.65, respectively, which were much lower than those of cSPAES.A series of SPAES-based blend membranes (SPAES-IPN) with interpenetrating polymer network (IPN) structure were prepared successfully from SPAESs with various IEC level. The scanning electron microscopy (SEM) proved the miscibility of the system and membrane uniformity. The SPAES-IPN membranes exhibited significantly improvement in dimensional and hydrolytic stability, and reasonably high proton conductivity was maintained. (). For example, for In70(IEC=1.95 meq/g), which showed 173mS/cm in water at 60℃, after aging in water for 24 h at 130℃, the dimensional changes in plane and thickness direction were 0.45, and 0.51, respectively.And this membrane also displayed much high toughness after aging in 130℃water for 200 h.Two series of SPAES/SPI and cSPAES/SPI blend membranes were prepared from SPAES (or cSPAES) and SPI. The miscible structure of the blend membranes was confirmed by SEM. Thermogravimetry analysis demonstrated that the blend membranes were stable up to 300℃. By the introduction of SPI, the blend membranes showed much higher hydrolytic stability and methanol tolerance than the corresponding SPAES (or cSPAES) membranes. The blend membranes showed higher proton conductivity than the corresponding SPI membranes in the whole range of relative humidity.Novel poly (2-(3-sulfo) benzoyl-1,4-phenylene)-block-polynaphthalimide (PSP-b-PI) copolymers were successfully synthesized by Ni(0) catalytic copolymerization of 2,5-dichloro-3'-sulfo-benzophenone and dichloro-terminated naphthalimide oligomer. TEM results suggested that microphase-separated structure for the hydrophilic domain and hydrophobic domain were presented in these membranes. PSP-b-PI membranes showed good hydrolytic stability at 130℃Although with high isotropic performance for the dimensional change, PSP-b-PI membranes showed anisotropic performance for proton conductivity. These membranes showed high through-plane conductivity in water as well as under low relative humidity. The PSP-b-PI membrane with IEC of 1.5 meq/g showed high PEFC performance.