Acid-doped poly benzimidazole

S. Suarez, N.K.A.C. Kodiweera, P. Stallworth, S. Yu, S.G. Greenbaum, B.C. Benicewicz, Multinuclear NMR study of the effect of acid concentration on ion transport in phosphoric acid doped poly(benzimidazole) membranes, J. Phys. 

Wang J-T, Savinell RF, Wainright J, Litt M, Tu H (1996) An H2-02 fuel cell using acid doped poly benzimidazole as polymer electrolyte . Electrochimica Acta 41 193. 

WAINRIGHT J s, WANG J T, WENG D, SAViNELL R F and LiTT M (1995), Acid-doped poly-benzimidazoles a new polymer electrolyte , J Electrochem Soc, 142, L121-L123. 

Gomez-Romero P, Asensio JA, Borr6s S (2005) Hybrid proton-conducting membranes for polymer electrolyte fuel cells. Phosphomolybdic acid doped poly(2,5-benzimidazole) -(ABPBI-H3PM012O40). Electrochim Acta 50 4715 720... 

Di SQ, Yan LM, Han SY et al (2012) Enhancing the high-temperature proton conductivity of phosphraic acid doped poly(2,5-benzimidazole) by preblending boron phosphate nanoparticles to the raw materials. J Power Sources 211 161-168... 

Phosphoric acid-doped (PA) poly-benzimidazole (PBI) films attain proton conductivities >0.25 S cm at temperatures above 150°C (Xiao et al 2005). The shift to higher temperatures of fuel cell operation, enabled by the use of these membranes, improves the fuel tolerance to carbon monoxide impurities, enhances the electrode kinetics, and alleviates humidification requirements. The problem is that the higher temperature not only accelerates the kinetics of desired electrode reactions, but also those of degradation processes. Moreover, PBI membranes function poorly under ambient conditions. PEFCs using PBI PEMs are suitable for residential applications, but they are currently not envisaged for automotive applications. 

Jeong et al. [69] synthesized acid-doped sulfonated poly(aryl ether benzimidazole) (s-PAEBI) copolymers for use in high-temperature fuel cells. The polymer was made in a direct polymerization (structure confirmed with NMR) and doped with phosphoric acid to levels of 0.7-5.7. The degree of sulfonation was varied from 0-60%. The copolymer s physicochemical properties were studied using AFM, TGA, and conductivity measurements. TGA runs showed good stability of the nonsulfonated, sulfonated, and acid-doped sulfonated membranes up to 450 °C, with a slow decline above this temperature. The conductivity depended on the doping level of the polymer. At 130 °C with no hiunidification, a polymer with a doping level of 5.7 had a conductivity of 7.3 X 10 S cm ... 

Figure 29.8 Structures of two basic polybenzitnidazoles (a) FBI and poly(2,5-benzimidazole), also known as AB-PBI and (b) schematic description of polymer matrix-assisted proton transport in phosphoric acid doped FBI.

Kreuer et al. [66] doped sulfonated poly(ether ether ketone) (sPEEK) by immersing it into liquid pyrazole and imidazole. A base doping level of 2.3-10, defined as the molar ratio of [C3N2H4]/[-S03H], could be achieved. The intercalation of imidazole and pyrazole into polymers with Brpnsted acid sites is shown to enhance the protonic conductivity. Of the two basic solvents of protons, pyrazole has a lower tendency for the molecular association by hydrogen bonding and therefore a lower proton conductivity, as compared with imidazole. Fu et al. [81, 82] studied acid-base blends based on 2-aminobenzimidazole and sPEEK. They proposed that benzimidazole is protonated by the sulfonic acid, as evidenced by the symmetric stretching of the S-O bonds in FTIR spectra. 

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