Acid-doped polybenzimidazole

The membranes formed via these two processes demonstrate different performance levels. Typically, the post-doped PEMs are stronger and tougher than directly cast membranes, which require a polymer of a higher inherent viscosity in order to prepare membranes with reasonable strength. In general, the conductivity of the directly cast membrane will be significantly higher than that of post-doped membranes [154]. 

Conduction in such a PBI electrolyte is heavily dependent on the doping level [155]. 

Over the acid doping range of200% to 560%, the activation energies range from 18 to 25 kJ niol . At a doping level of 200%, membrane conductivity is approximately 

5 X 10 S cm at 200 °C, and the presence of free or unbound acid is necessary to improve the transport. At a doping level of 570% phosphoric acid, the conductivity is 

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, 

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Savadogo, O. and Xing, B., Hydrogen/oxygen polymer electrolyte membrane fuel cell (PEMFC) based on acid-doped polybenzimidazole (PBI), J. New Mater. Electrochem. Syst., 3, 345, 2000. 

Wainright, J.S. et ah. Acid-doped polybenzimidazoles a new polymer electrolyte, J. 

Samms, S.R., Wasmus, S., and Savinell, R.F., Thermal stability of proton conducting acid doped polybenzimidazole in simulated fuel cell environments, J. Electrochem. Soc., 143, 1225, 1996. 

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. 

J.T. Wang, R.F. Savinell, J. Wainright, M. Lift, and H. Yu. A H-2/0-2 fuel cell using acid doped polybenzimidazole as polymer electrolyte. Electrochimica Acta A, 193-197 1996. 

Wainright JS, Wang JT, Weng D, Savinell RF, Litt M (1995) Acid-doped polybenzimidazoles—a new polymer electrolyte. J Electrochem Soc 142 L121-L123... 

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... 

C. Hasiotis, L. Qingfeng, V Deimede, J.K. Kallitsis, C.G. Kontoyannis and N.J. Bjerrum, Development and characterization of acid doped polybenzimidazole/ sulfonated polysulfone bend polymer electrolytes for fuel cells, J. Electmchem. Soc., 2001, 148, A513-A519. 

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]. 

In the search for PEMs with lower alcohol permeability than Nafion and other perfuorinated membranes, without degradation of the proton conductivity, a number of new polymeric membranes were synthetized and characterized, such as sulfonated polyimides, poly(arylene ether)s, polysulfones, poly(vinyl alcohol), polystyrenes, and acid-doped polybenzimidazoles. A comprehensive discussion of the properties of these alternative membranes is given in Chap. 6, along with those of Nafion and Nafion composites. 

Wang J-T, Wainright JS, Savinell RF, Lilt M (1996) A direct methanol fuel cell using acid-doped polybenzimidazole as polymCT electrolyte. J Appl Electrochem 26 751-756... 

Bouchet R, Siebeit E (1999) Protrai conduction in acid doped polybenzimidazole. Solid State Ion 118 287-299... 

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... 

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. 

X. Glipa, B. Bonnet, B. Mula, D.J. Jones, J. RozieAre, Investigation of the conduction properties of phosphoric and sulphuric acid doped polybenzimidazole, J. Mater. Chem. 9 (12)(1999) 3045-3049. 

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