Study On Sulfonated Poly(Aryl Ether)s Containing Phthalazinone Moieties As Proton Exchange Membranes

Proton exchange membrane fuel cell (PEMFC) has been considered as a promising alternative engergy source because of their high efficiency, high power density and friendly environment. Proton exchange membrane (PEM) is a vital part of the PEMFC system. In order to qualify for the applications of fuel cell, PEM must combine a number of properties such as excellent chemical stability especially against attack of oxygen, suitable water uptake and swelling ratio, high proton conductivity and adequate mechanical properties. PEM traditionally used in PEMFC are perfluorosulfonic acid PEMs, such as DuPont's Nafion^?, because of their excellent chemical and mechanical stabilities as well as high proton conductivity, However, they have the disadvantages of high cost, low operation temperature and high fuel permeability which have limited their widely applications. In order to overcome these disadvantages, much more attention has been paid to search for the alternative materials with high performance, long life and low cost.Sulfonated poly(aryl ether)s containing phthalazinone moieties have high thermal stability and excellent mechanical strength, and lower cost compared with the perfluorosulfonic acid polymer of present fuel cell membranes.Sulfonated poty(phthalazinone ether ketone) (SPPBEK), sulfonated poly(phthalazinone ether nitrile ketone) (SPPENK) and sulfonated poly(phthalazinone ether sulfone ketone) (SPPESK) with different DS were obtained by direct aromatic nucleophilic polymerization from phthalazinone-containing bisphenol monomer and sulfonated dichloro, or difluoro monomers, respectively. The results indicated that the T_g, 5% weight loss temperature and proton conductivity of the same series of polymers increased with the increasing of DS and theσof SPPESK was higher than that of SPPENK in the same DS. Sulfonated poly(aryl ether)s containing phthalazinone moieties had low cost, high thermal stability and excellent mechanical strength, and the polymers with DS around 1.0 have high proton conductivities (σ).Acid-base composite membranes were composed of sulfonated polymers as the acidic components and polyetherimide (PEI) as the basic component. Influence of PEI content on acid-base composite membrane properties was studied. Acid-base composite membranes showed moderate swelling with very good thermal stabilities, high oxidative stabilities and good mechanical properties. However, theσof acid-base composite membranes was lower than that of corresponding pure membranes. The 5% weight loss temperature of SPPBEK-120/PEI-10 was 441℃, it's swelling ratio was 6.5% at 80℃, theσwas 5.2×10^-2S/cm at 95℃and it's tensile strength was 38.3MPa, which indicated the potential as promising PEMs for fuel cells applications.By the sol-gel process, the HPAs and H₃PO₄ supported on silica gel. The organic-inorganic composite membranes composed of inorganic proton conductors in silica gel and sulfonated poly(aryl ether)s containing phthalazinone moieties were obtained by dissolving HPAs/SiO₂, H₃PO₄/SiO₂ and sulfonated polymers in'NMP, respectively. Influence of inorganic proton conductors in silica gel content on composite membrane properties was studied. The introduction of inorganic proton conductors in silica gel not only increased proton conductivities, but also decreased the lost of conductive materials after immersed in water. The 5% weight loss temperature of SPPESK-45-10 was 326℃, it's swelling ratio was 9.6% at 80℃, it's tensile strength was 46.8MPa and theσwas 1.1×10^-1S/cm at 95℃, which multiplied three-fold comparing with pure membranes and higher than that of Nafion^?117 measured under the same conditions. When immersed in water for 4d, less than 2% PWA was found lost in the SPPESK/PWA/SiO₂ membrane. But the dispersion of SiWA, PMoA and H₃PO₄ in composite membranes was poor, which limited the contents of inorganic proton conductors in membranes and the properties of membranes.SPPENK/BPO₄ composite membranes were obtained by boron phosphate into the SPPENK matrix from tripropylborate (C₃H₇O)₃B and phosphoric acid (H₃PO₄) precursors via film processing. SPPENK/BPO₄ composite membranes had high thermal stabilities, good film-forming properties and high proton conductivities. The-proton conductivity of SPPENK/BPO₄ composite membrane with the 10% BPO₄ was 3.5×10^-2S/cm at 95℃, which increased around two-fold comparing with pure membrane. When immersed in water for 4d, no obvious change in composite membrane's proton conductivity, which showed good stability of BPO₄ particle in composite membranes.