SPEEK composite membranes

Some PBI composites membranes have also been studied in relation to methanol barrier properties. The relative permeability for PBl/Nafion composites (0.055 < Pr < 0.70) [106, 107] has been discussed in Sect. 6.5.6 (see Fig. 6.23), and it is clear that the blend membranes is a better methanol barrier than pure Nafion, but it is worst methanol barrier than pure PBI. Wycisk et al. [415] studied the properties of PBI/sPOP membranes and found that the relative permeability of pure sPOP membranes is reduced from P = 0.56 down to P = 0.028 by adding 12 wt% of PBI. A similar effect has been found for PBI/sPEEK composite membranes, where the permeability of pure sPEEK is reduced by a factor 50 by adding 20 wt% of PBI [416]. 

Sol-gel-derived SPEEK-Ti02 hybrid membranes (with varied nanosized Ti02 content) showed improvement in water uptake and its retention along with reduction in methanol permeability [67]. Tripathi and Shahi [68] reported a polyaniline surface-modified SPEEK composite membranes of nanosized Si, Zr, and Ti oxides by sol-gel to achieve extremely low methanol permeability due to a synergetic effect, without any sacrifice in membrane... 

Recently, they fabricated the polytetrafluoroethylene (PTFE)-reinforced SPEEK composite membranes to improve their chemical stability and ion selectivity in VRB applications. Compared to pristine SPEEK membranes, the composite membranes exhibited the lower swelling ratio and higher mechanical stability due to the PTFE reinforcement. As expected, the SPEEK/PTFE membranes showed much higher coulombic efficiency and energy efficiency than those of SPEEK membrane. In addition, the composite membranes exhibited much better stability than pristine SPEEK under VRB operating conditions. 

Bello, M., Javaid Zaidi, S.M., and Rahman, S.U. (2008) Proton and methanol transport behavior of SPEEK/ TPA/MCM-41 composite membranes for fuel cell application. /. Membr. Sd., ill (1), 218-224. 

Zhang et al. [128] synthesized a self-humidifying membrane based on a sulfonated poly(ether ether ketone) (SPEEK) hybrid with a sulfated zirconia (SO / ZrO2, SZ) -supported platinum catalyst (Pt-SZ catalyst). This type of composite membrane has a higher proton conductivity than plain SPEEK, due to the effect of the Pt-SZ catalyst the membrane also provided excellent single cell performance at low humidity. 

The in situ construction of the inorganic component within a cast polymer solution is not limited to metal oxides and in practice a range of other inorganic materials can be formed depending on the choice of precursor(s) incorporated in the polymer solution, and the nature of post-treatment following solvent removal. Roziere and Jones and co-workers have developed nano composite membranes in which zirconium phosphate is formed from zirconyl propionate introduced into a DMAc solution of sPEEK, by immersion of the cast film, after solvent removal, into phosphoric acid. This approach provides a robust synthetic route that can be generalised to other ionomers, and allows the amount of ZrP to be readily varied, even up to ca. 40-50 wt. %. 

S.M.). Zaidi, Preparation and characterization of composite membranes using blends of SPEEK/PBl with boron phosphate. Electrochimica Acta 50 (2005)... 

The acid-base Nafion composite membranes include blends of Nafion with polypyrrole (PPy) [98-104], polybenzimidazole (PBI) [105-107], poly (propyleneoxide) (PPO) [108, 109], polyfurfuryl alcohol (PFA) [110], poly(vinyl alcohol) (PVA) [111-115], sulfonated phenol-formaldehyde (sPF) [116], polyvinylidene fluoride (PVdF) [117-122], poly(p-phenylene vinylene) (PPV) [123], poly(vinyl pyrrolidone) (PVP) [124] polyanifine (PANI) [125-128], polyethylene (PE) [129], poly(ethylene-terephtalate) [130], sulfated p-cyclodextrin (sCD) [131], sulfonated poly(ether ether ketone) (sPEEK) [132-135], sulfonated poly(aryl ether ketone) (sPAEK) [136], poly(arylene ether sulfone) (PAES) [137], poly(vinylimidazole) (PVl) [138], poly(vinyl pyridine) (PVPy) [139], poly (tetrafluoroethylene) (PTFE) [140-142], poly(fluorinated ethylene-propylene) [143], sulfonated polyhedral oligomeric silsesquioxane (sPOSS) [144], poly (3,4-ethylenedioxythiophene) (PEDT) [145, 146], polyrotaxanes (PR) [147], purple membrane [148], sulfonated polystyrene (PSSA) [149, 150], polystyrene-b-poly(ethylene-ran-butylene)-bpolystyrene (SEES) [151], poly(2-acrylamido-2-methyl-l-propanesulphonic acid-co-l,6-hexanediol propoxylate diacrylate-co-ethyl methacrylate) (AMPS) [152], and chitosan [31]. A binary PVA/chitosan [153] and a ternary Nafion composite with PVA, polyimide (PI) and 8-trimethoxy silylpropyl glycerin ether-1,3,6-pyrenetrisulfonic acid (TSPS) has also been reported [154]. 

Inorganic/PVA composites have been also considered, including sulfonic or phosphonic modified silica, titania, hydroxyapatite, heteropoly acids, zirconium phosphate, and montmorillonite. Hybrid organic-inorganic PVA composite membranes, like PVA/Ti02/PSSA, PVA/SiOa/SSA/, PVA/PWA/sPEEK/PWA, PVA/Si02/PPA, etc., have been reported. 

There are several sPEEK membranes with very good relative selectivity and several sPEEK composites with silica, zirconia and their mixtures with heteropolyacids [370, 371, 377] which exhibit remarkable selectivities with high proton conductivities. Composites of sPAEK with epoxy resin [383] and crosslinked with PVA [386] also show excellent selectivities and high conductivities. Unfortunately, the performances of these promising membranes in DMFC have not been reported yet. 

Ternary composites of PBI with sPEK + polysulfone (PSU) [437], sPEEK + sulfonated PSU (sPSU) [438], and sPEEK + zirconium phosphate [439] were studied in DMFC. Excellent results were reported for DMFC, at 110 °C, using the first two composite membranes. 

Gao Q, Wang Y, Xu L, Wei G, Wang Z (2009) Proton-exchange sulfonated poly(ether ether ketone) (SPEEK)/SiOx-S composite membranes in direct methanol fuel cells. Chinese J Chem Eng 17 207-213... 

Li X, Liu C, Xu D, Zhao C, Wang Z, Zhang G, Na H, Xing W (2006) Preparation and properties of sulfonated poly(ether ether ketone)s (SPEEK)/polypyrrole composite membranes for direct methanol fuel cells. J Power Sources 162 1-8... 

Li H, Zhang G, Ma W, Zhao C, Zhang Y, Han M, et al. Composite membranes based on a novel benzimidazole grafted PEEK and SPEEK for fuel cells. Int J Hydrogen Energy 2010 35(20) 11172-9. 

The proton conductivity of SPEEK membrane can be improved by incorporating a fast proton conductor in the polymer matrix as studied by Silva et al. (2005). They utilized zirconium phosphate (ZrPh) pretreated with -propylamine and then with PBI. The pretreatment was to improve the compatibility between ZrPh and SPEEK. Even though the compatibility of the inorganic was good, the proton conductivity and water uptake of the composite membrane were reduced, consequently reducing the methanol permeability. 

FIGURE 13.9 Water uptake of SPEEK/BPO4 composite membranes as a function of BPO4 loading. (Reprinted from Othman, M.H.D., Ismail, A.F., and Mustafa, A., J. Memb. ScL, 299, 156-165, 2007. With permission.)... 

As a conclusion, SPEEK/BPO4 composite membrane has been successfully prepared and characterized, specifically for DMFC application. In terms of the... 

Results of methanol permeability at various DS, SiWA, and Si02 are plotted in Figure 13.15. It can be seen that no membrane possesses higher methanol permeability than the Naflon 112 membrane. The corresponding methanol permeability for Nafion 112 was about 15.07 x 10 cm%. The methanol permeabilities of composite membranes based on SPEEK are obviously lower than that of Naflon 112, which is possibly due to the microstructure differences between the SPEEK and the Naflon 112 membrane. Kreuer reported that the Naflon membrane has high hydrophobicity of the perfluorinated backbone and also high hydrophilicity of the sulfonic groups (Kreuer 2001). In the presence of water, this character is more pronounced and consequently increases the hydrophobic/hydrophilic domains of the Naflon membrane. 

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