Silica/Nafion composite membrane

Yen CY, Lee CH, Lin YF, Lin HL, Hsiao YH, Liao SH, Chuang CY, Ma CCM (2007) Sol-gel derived sulfonated-silica/Nafion composite membrane for direct methanol fuel cell. J Power Sources 173 36 14... 

Modeling of polymer membrane structure through dynamics simulations is generally coupled with the water/proton-transfer properties. Yana et al. conducted molecular dynamics (MD) simulations of Krytox-Silica-Nafion composite membranes in comparison to the pure Nation. A 5 wt% of carboxylic acid terminated perfluoropolyether hybrid with silica (Krytox-Silica) in Nation composite polymer was used in the modification of a PEM in order to improve its efficiency at high operating temperatures. MD simulations were carried out in order to understand the microscopic properties of two systems, Krytox-Silica in Nation and pure... 

Gosalawit, R., Chirachanchai, S., Manuspiya, H., Traversa, E., Krytox-Silica-Nafion composite membrane A hybrid system for maintaining proton conductivity in a wide range of operating temperatures, Catal. Today, 2006, 118, 259-265. 

Jin Y, Qiao S, Zhang ZP, Xu ZP, Smart S, Diniz da Costa JC, Lu GQ (2008) Novel Nafion composite membranes with mesoporous silica nanospheres as inorganic fillers. J Power... 

Yuan, J.J., Zhou, G.B., Pu, H.T. (2008) Preparation and properties of Nafion / hollow silica spheres composite membranes. Journal of Membrane Science, 325, 742-748. 

Most of the silica-based Nation nanocomposite membranes have exhibited superior cell performance compared to that of the pristine Nation. The addition of TBS to Nation-silica nanocomposite significantly increased the electrochemical properties of the membrane. Nafion-silica-TBS nanocomposite has a current density of 1600 mA cm at 0.6 V and 1100 mW cm (maximum power density), compared to 999 mA cm of Nation at 0.6 V and 838 mW cm . Nafion-silica-Zr02 composite membranes have superior cell performance at 120°C and low RH compared to those of the VN and Nafion-Zr02 membrane. Addition of HPMC to SPEEK-silica nanocomposites improves the current density of the nanocomposites irrespective of the change in RH. The current densities of SPEEK-silica-HPMC, SPEEK-silica nanocomposites, and Nation were 785, 598, and 176 mA cm", respectively, under 70% RH and 0.4 V cell potential, with power densities of 126,161, and 27 mW cm , respectively, under 10% RH and 80°C. Addition of Laponite to SPPEK was noted to achieve the current density of 370 mA cm compared to 80 mA cm for SPEEK at 0.6 V (see Table 9.7). 

Yana, J., Nimmanpipug, R, Chirachanchai, S., Gosalawit, R., Dokmaisrijan, S., Vannarat, S., Vilaithong, T., Lee, V.S., Molecular dynamics simulations of Krytox-Silica-Nafion composite for high temperature fuel cell electrolyte membranes. Polymer, 2010, 51, 4632-4638. 

Most of the reported inorganic fillers used to modify Nafion are composite where the inorganic particles (usually nanoparticles) are located in the membrane bulk. Most of them are prepared using the recast method, where the filler nanoparticles dispersed in a solvent are mixed with Nafion ionomer dispersion in the same solvent or a compatible one. The solution is cast on a Petri dish or a plane surface at high temperature to form the recast composite membrane. An alternative method adopted to prepare Nafion composites with silica [31, 32, 41, 95], functionalized silica [35], and zirconium and titanium phosphate [41], is the in situ sol-gel reaction method, schematized in Fig. 6.5. 

In the case of Si02/Nafion composites the Nafion membrane is swollen in water and methanol and immersed in a methanol solution of silicon tetraetoxysilane (TEOS). Thus, the TEOS hydrolysis take place inside the membrane and the amount of formed Si02 inside the membrane depends on the impregnation time. Einally the membrane is dried at high temperature to remove trapped volatiles and promote further silica network condensation [32]. 

Fig. 6.5 Scheme of preparation of composite silica/Nafion membranes by sol-gel reaction (Adapted from Ref [9])... 

It is interesting to analyze the effect of inorganic fillers or blending with other polymers on the methanol uptake of Nafion-based membranes. Kim et al. [46] measured methanol uptake in composite of Nafion with organic modified silica (ORMOSIL) and they observed that the methanol uptake decrease proportionally to the amount of inorganic phase in the membrane, reaching a half of its value in Nafion when the filler content is close to 40 wt%. The connectivity between the... 

Lin Y, Yen C, Ma CM, Liao S, Lee C, Hsiao Y, Lin H (2007) High proton-conducting Nafion/-S03H functionalized mesoporous silica composite membranes. J Power Sources 171 388-395... 

Jiang R, Kunz HR, Fenton JM (2006) Composite silica/Nafion membranes prepared by tetraethylorthosilicate sol-gel reaction and solution casting for direct methanol fuel cells. J Membr Sci 272 116-124... 

Ren et al. also reported that the water uptake by the membrane containing oxide is higher than that by the pristine Nafion (Ren et al. 2005). Nafion-silica man-branes have been prepared employing several methods by casting mixtures such as silica powder, diphenylsilicate (DPS), sol-gel reaction with tetraethylorthosilicate (TEOS), followed by solution casting of the Nafion solution, phosphotungstic acid (PTA)-doped composite silica/Nafion/PTA, and silica oxide (Wang et al. 2007). 

The conductivity tests were carried out for a number of P(VDF-CTFE)/ Nafion/Inorganic membranes 3D phase zirconium phosphate, 3D porous titanosili-cate, amorphous zirconium phosphate (AZP), mesoporous alumina, and a silica-based commercial molecular sieve (MS). Figure 12.12 shows the conductivity of various PEM composite membranes under various humidity conditions. The inorganic phase... 

The composite membrane approach can also be used for membranes alternative to Nafion such as sulfonated polyetherketones and polysulfones. Sulfonated polysulfone is one of the most promising polymers for PEMs due to its low cost, commercial availability, and easy processability. Composite polysulfone-based membranes based on silica have been prepared and characterized for DMFC to extend the operating temperature up to 120 °C [16]. As an example, the following describes the preparation and characterization of a... 

Electrochemical characterizations of DEFCs at high temperatures (90-145 °C) have been carried out on using Nafion-Si02 composite membrane as electrolyte and 1.5 M ethanol solution at the anode. The composite membrane composed by Nafion ionomer and silica shows advantageous water retention properties at high temperatures (90-145 °C) useful for the DEFC process. 

Composite PSFA—silica membranes have been demonstrated for water electrolysis. Composite membrane containing 3 wt% Si02 (Cab-O-Sil EH5, Cabot) for water electrolysis were prepared by using a combination of recast and thermal treatment procedures. The thickness of the composite membrane was comparable to Nafion 115, i.e., 120 jim. The membrane forming procedure is exemplified in Fig. 2.17. 

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