High Temperature Polymer Electrolyte Membrane Fuel Cells by Qingfeng Li David Aili Hans Aage Hjuler & Jens Oluf Jensen

Author:Qingfeng Li, David Aili, Hans Aage Hjuler & Jens Oluf Jensen
Language: eng
Format: epub
Publisher: Springer International Publishing, Cham

13.2.2 Preparation of PBI Composite Membranes with Hygroscopic Oxides

Although it is said that the silica is added to the PBI structure, the reality is that, in most of the cases, the silica is modified or functionalized in order to improve their characteristics of the PBI composite membrane. The incorporation of inorganic nanofillers in the polymer matrix is often carried out by in situ sol–gel creation of the particles during membrane casting [12, 13]. This method avoids silica nanoparticles agglomeration and therefore enables higher inorganic contents [14].

Mustarelli et al. [23] functionalized silica with imidazole by means of a standard basic hydrolysis/condensation process, starting from tetraethoxysilane (TEOS) and N-(3-triethoxysilylpropyl)-4,5-dihydroimidazole. Then the active silica was added to a PBI solution and finally, by a well-known casting method the PBI composite membranes can be prepared. A similar procedure was followed to prepared PBI–silica nanocomposite membranes, via sol–gel process from an organosoluble, fluorine containing copolymer with a silica precursor, TEOS, and a bonding agent to reinforced interfacial interaction between PBI chains and silica nanoparticles [19, 24]. More recently, the research group headed by Mustarelli prepared poly(2,2,-(2,6-pyridine)-5,5,-bibenzimidazole) (PBI-5N) composite membranes containing PBI functionalized silica particles or mesoporous silica MCM-41 [25]. Silica nanoparticles (diameter 10–20 nm) and sulfonated silica nanoparticles prepared in the lab according to a method reported elsewhere [26] were added to a PBI solution in N,N-dimethylacetamide to get nanocomposite PBI membranes with different fillers contents from 5 to 20 wt% [27]. A similar procedure was used for TiO2-based composite PBI membranes prepared by the group of Lobato et al. [28–31]. On the other hand, modified TiO2 and SiO2 nanoparticles were added to a poly[2,2-5,5-(m-pyrazolidene)-bibenzimidazole] (PPBI) solution and by a casting method the composite PBI-based membrane was obtained [32]. The modification of both SiO2 and TiO2 nanoparticles was achieved by radical polymerization of some vinyl monomers such as sulfonated polyvinylbenzene (PSV) or poly vinylimidazole (PVI) on the surface of the nanoparticles to which vinylic groups were bonded covalently.

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