Polybenzimidazoles phosphoric acid

Litt M, Ameri R, Wang Y, Savinell RF, Wainright JS (1999) Polybenzimidazoles/phosphoric acid solid polymer electrolytes mechanical and electrical properties. Mater Res Soc Symp Proc 1999 313-323... 

Conti F, Majerus A, Di Noto V et al (2012) Raman study of the polybenzimidazole-phosphoric acid interactions in membranes for fuel cells. Phys Chem Chem Phys 14 10022-10026... 

Modeling polybenzimidazole/phosphoric acid membrane behaviour in a HTPEM fuel cell. In ... 

Acid-Doped Polybenzimidazole Phosphoric-acid-doped polybenzimidazole (PBI see Fig. 29.8a) fuel cell membranes were developed some 13 years ago at Case Western Reserve University (Wainright et al., 1995). Researchers found that a significant amount of phosphoric acid could be absorbed into a PBI film without scarifying the mechanical strength of the membrane. The sorbed acid species conduct protons in the absence of... 

Li, Q., Hjuler, H.A., and Bjerrum, N.J., Phosphoric acid doped polybenzimidazole membranes physiochemical characterization and fuel cell applications, J. Appl. Electrochem., 31, 773, 2001. 

A. Schechter and R.F. Savinell. Imidazole and 1-methyl imidazole in phosphoric acid doped polybenzimidazole, electrolyte for fuel cells. Solid State Ionics 147, 181-187 2002. 

R.H. He, Q.F. Li, G. Xiao, and N.J. Bjerrum. Proton conductivity of phosphoric acid doped polybenzimidazole and its composites with inorganic proton conductors. Journal of Membrane Science 226, 169-184 2003. 

Numerous communications describe the use of hi -temperature solution polymerization techniques. Of the solvents used, poly(phosphoric acid), introduced in 1964 into polybenzimidazole chemistry by Iwakura et al. doubtlessly occupies the first position, and a great many syntheses employing the poly(phosphoric add) solution technique have since been reported from various polymer laboratories " Iwakura s technique offers an advantage insofar as the tetraamine monomers may be employed as the stable and easy-to-handle hydrochlorides in place of the extremely air-sendtive free bases. In addi-... 

As D Alelio s patent embodies conditions of low omdensation temperatures and so, just like some of the aforementioned solution polymerizations , teaches a>nditions beneficial to reactant and nx>duct integrity, it permits the preparation of polybenzimidazoles from monomers too unstable thermally or chemically for use in the melt or poly(phosphoric acid) solution processes, examples of sudi monomers being te-trahaloterephthalaldehydes or the crosslinkable 3-vin)fisophthalaldehyde. It does not, however, provide for the isolaticm and application of prepolymers and, thus, for utilization of die two-stage approadi so beneficial from a processing and application standpoint. 

Polybenzimidazole - the polymer used as membrane in the fuel cell is intermixed with neat phosphoric acid... 

Figure 10.8 Chemical structure of (a) polybenzimidazole (PBI) and (b) phosphoric acid-doped PBI.

Figure 23.10 Proton conductivity of a few prototypical proton conducting separator materials Nafion as a representative of hydrated acid ionomers (see also Fig. 23.2(a) [43, 78], a complex of PBI (polybenzimidazole) and phosphoric acid as a representative of adducts of basic polymers and oxo-acids (see also Fig. 23.2(b)) [16], phosphonic acid covalently immobilized via an alkane spacer at a siloxane backbone (see also Fig. 23.2(c)) [127], the acid salt CsHSO, [125] and an Y-doped BaZrOj [126].

To prepare new and inexpensive membranes, various trials have been made 196 sulfonated aromatic polyether membrane such as polyether ketones (PEEK),197 sulfonated polysulfone198 and membranes from sulfonated polyphenylene sulfide,199 phosphoric acid-doped polybenzimidazole, (PBI),200 polybenzimidazole having sulfonic acid groups,201 polybenzimidazole with phosphonic acid groups,202 a blend membrane of polybenzimidazole and sulfonated polysulfone,203 sulfonated phosphazene polymer.204... 

Figure 17.3.16 Results for oxidation of formic acid (dotted curves) and methanol (solid curves) at a fuel-cell anode (Pt/Ru) with phosphoric-acid-doped polybenzimidazole polymer electrolyte, 170°C. (a) current density and (b) mass signal for CO2 at a scan rate of 1 mV/s. [From M. Weber, J.-T. Wang, S. Wasmus, and R. F. Savinell, J. Electrochem. Soc., 143, L158 (1996), reprinted by permission of the publisher. The Electrochemical Society, Inc.]...

Another approach was the synthesis of inorganic/organic composite materials to influence the properties of the membrane. An overview on the state of the art of composite perflourinated membranes is given in [15]. Infiltration of a polymer carrier material with various inorganic proton conductors is subject of a patent [16]. For operation at elevated temperature, several materials have been considered, hi an early work, Nafion /Fl3P04 showed better conductivity at temperatures above 100°C compared with blank Nation and also reduced methanol permeabihty [17]. New types of polymers are also under development for better temperature stabihty one of the most advanced examples is the high-temperature material polybenzimidazole, which usually is doped with phosphoric acid [18]. 

Polybenzimidazole films doped with phosphoric acid have also been investigated for direct methanol fuel cells. These membranes, however, only display the requisite conductivities at high temperatures and have only been demonstrated in vapor feed systems operated at 150-200 C. Thus, although these novel membrane applications have been demonstrated to have decreased methanol permeability in fuel cells, none of the systems have been successful in being applied to low temperature liquid-feed direct methanol fuel cells. 

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