Polybenzimidazole proton conductivity

Thomas OD, Peckham TJ, Thanganathan U et al (2010) Suifonated polybenzimidazoles proton conduction and acid-base crosslinking. J Poiym Chem A Poiym Chem 48 3640-3650... 

Thomas, O. D. Peckham,T. J. Thanganathan,U. Yang,Y. Holdcroft,S.,Sulfonated polybenzimidazoles proton conduction and add-base crosslinking,/ Polym. Sci. PartA Polym. C/zem., 48,3640-3650 (2010) DOI 10.1002/pola.24147... 

Hoel, D. and Grunwald, E., High protonic conduction of polybenzimidazole films, J. Phys. Chem., 81, 2135, 1977. 

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. 

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. 

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].

As shown in Fig. 14, PIM-1 and PIM-7 have been found to exhibit substantially higher O /Nj selectivities (a(O2/N2)>3.0) than other polymers of similar permeability [41]. Other thermally rearranged [78] polyimides show excellent CO /CH separation selectivities. These materials were also shown to function as fuel cell membranes when doped with H3PO4 and proton conductivities of 0.15 S cm" were observed at 130°C [78] that is, higher than polybenzimidazole membranes. 

Polybenzimidazole (PBI) (initially manufactured by Hoechst-Celanese, now PE ME A) is one of the few polymers under consideration for high-temperature operation. The application of PBI [206, 207] and the noncommercial AB-PBI [208] in fuel cells was introduced by Savinell and coworkers. For that, the membrane was immersed in concentrated phosphoric acid to reach the needed proton conductivity. Operation up to 200 °C is reported [209]. A disadvantage of this class of membranes is the acid leaching out during operation, particularly problematic for cells directly fed with liquid fuels. Additionally, the phosphoric acid may adsorb on the platinum surface. A review on membranes for fuel cells operating above 100 °C has been recently published [209]. 

M.Y. )ang, Y. Yamazaki, Preparation, characterization and proton conductivity of membrane based on zirconium tricarboxybutylphosphonate and polybenzimidazole for fuel cells. Solid State Ionics 167 (2004) 107-112. 

P. Staiti, M. Minutoli, Influence of composition and acid treatment on proton conduction of composite polybenzimidazole membranes. Journal of Power Sources 94 (2001) 9-13. 

P. Staiti, Proton conductive membranes constituted of silicotungstic acid anchored to silica-polybenzimidazole matrices, Journal of New Materials for Electrochemical Systems 4 (2001) 181-186. 

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. 

Carollo A, Quartarone E, Tomasi C, Mustarelli P, Belotti F, Magistris A, Maestroni F, Parachini M, Garlaschelli L, Righetti PP (2006) Developments of new proton conducting membranes based on different polybenzimidazole structures for fuel cells applications. J Power Sources 160 175-180... 

Pu H, Liu Q (2004) Methanol permeation and proton conductivity of polybenzimidazole and sulfonated polybenzimidazole. Polym Int 53 1512-1516... 

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. 

Polybenzimidazole (PBI) is an amorphous thermoplastic with a high glass transition temperature (T ) of 425°C-436°C (Li et al. 2003c) and demonstrates excellent thermal, chemical, and mechanical stabilities (Zhang et al. 2008.). Moreover, PBI exhibits a good protonic conductivity even at low relative humidity (Bouchet and Siebert 1999). PBI has to be doped with several acids, such as sulfuric acid and phosphoric acid, in order to improve its conductivity. The acid acts as both donor and acceptor in proton transfer and therefore allows for proton migration along the anionic chain. PBI also showed lower methanol permeability (Pivovar et al. 1999). 

One of the frequently advertised advantages of the phosphoric acid imbibed polybenzimidazole systems is their zero water drag coefficient and their possibihty to operate with dry hydrogen and oxygen. However, a vast literature has been devoted to the study of the proton conduction and the effect of relative humidity on the conductivity of the PBl-phosphoric acid system. The promoting effect and the physicochemical interactions of water vapors with the polymer electrolyte and on the fuel cell performance have been explicitly shown for the PBl/PPy(50)coPSF 50/50 polymer blend imbibed with phosphoric acid under fuel cell conditions. ... 

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