Phosphoric acid-doped

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. 

Q.F. Li, H.A. Hjuler, and N.J. Bjerrum. Phosphoric acid doped polyhenzimidazole membranes Physiochemical characterization and fuel cell applications. Journal of Applied Electrochemistry 31, 773-779 2001. 

PPS doped with AsFs dissolves readily in AsFs, but cast films are no longer soluble. Frommer has suggested that the solubilization mechanism involves solvation of both reactive radical intermediates and dopant counterions.f In addition, dialkyl esters of phosphoric acid dope PANi and render it soluble in certain solvents such as decalin. The resulting solutions can be mixed with conventional polymers and used to prepare films and fibers. 

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

An electro-osmotic drag due to proton migration is defined as the number of water molecules moved with each proton in the absence of a concentration gradient For comparison, the electro-osmotic drag coefficient for vapor or liquid-equilibrated Nafion membranes ranges from 0.9 to 3.2 at room temperature [146]. For phosphoric acid-doped PBI membranes, however, the water drag coefficient is dose to zero [149,... 

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.]...

Normal PEFC operating temperatures using PFSA or polyaryl membranes are in the range of 80 °C with new developments aiming at temperatures up to 120 °C [3, 4]. Higher operating temperatures up to 180 °C can be achieved with phosphoric acid doped polybenzimidazole membranes [5]. 

A commercial phosphoric acid doped PBI membrane, Celtec V by BASF Fuel Cells, tailored for DMFC is based in a blend of PBI and poly(vinyl phosphonic acid) (PVPA). The PVPA poly acid is immobilized in the PBI matrix by interpenetration, crosslinking and covalent bonding [201]. 

The methanol uptake of a grafted Nafion/poly(glycidyl methacrylate) membrane was studied by Mohy Eldin et al. [162]. The membrane, its amine derivate, and the phosphoric acid -doped membrane exhibit an important enhance of the methanol and water uptake with increasing grafting percentages. 

Nores-Pondal FJ, Buera MP, Corti HR (2010) Thermal properties of phosphoric acid-doped polybenzimidazole membranes in water and methanol-water mixtures. J Power Sources 195 6389-6397... 

Poly(2,2 -( 1,4-phenylene)5,5 -bibenzimidazole) can be obtained under certain conditions of polymerization as a high-molecular-weight species [29]. The polymer solutions can be used directly for phosphoric acid doped PBI membranes. Such membranes show high phosphoric acid doping levels. At 160 °C a high carbon monoxide tolerance for fuel cells is observed. 

A high-temperature operation of proton exchange membrane fuel cells can be achieved by acid-base polymer membranes [13]. A phosphoric acid doped PBI membrane is a valuable and successful device in the field. 

Copolymers with benzimidazole and benzoxazole units have been prepared and used as a polymer electrolyte material [30,11]. The polymer electrolyte material has both high proton conductivity and excellent mechanical properties even when it is obtained by in situ phosphoric acid doping. The polymer electrolyte material may substitute for the conventional phosphoric acid doped polybenzimidazole in a polymer electrolyte membrane fuel cell, particularly in a high-temperature polymer electrolyte membrane fuel cell. 

Yu S, Zhang H, Xiao L, Choe EW, Benicewicz BC. Synthesis of poly (2,2 -(L4-phenylene) 5,5 -bibenzimidazole) (para-pbi) and phosphoric acid doped membrane for fuel cells. Fuel Cells 2009 9(4) 318-24. 

Fontanella et al. reported on the use of phosphoric acid-doped PBI membranes for use in DMFCs and hydrogen/air PEM fuel cells (Fontanella et al. 1998). The membrane was designed to operate at a high temperature (150°C). A 10-fold decrease in methanol permeability with high ionic conductivities (-0.04 S/cm) was observed at a cell-operating temperature of 150°C. The major drawback of this membrane is that the proton-conducting acid is not chemically bound to the polymer. Any contact with a liquid methanol feed will leach the acid from the membrane and lower the membrane s proton conductivity. Thus, only methanol vapor feed can be employed with this membrane. 

The most common and effective route for the lab scale synthesis of mPBI is the high temperature (170-200°C) polycondensaton of tetraaminobiphenyl and isophthahc acid in polyphosphoric acid (PPA), Fig. 1. mPBI is a completely amorphous thermoplastic polymer with a glass transition temperature of aroimd 420°C. Phosphoric acid doped mPBI exhibits high thermal stability, " low... 

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