Polybenzimidazole membranes acid doping

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... 

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. 

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. 

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. 

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... 

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. 

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. 

Figure 2. (a) Weight increases of FBI membranes after being immersed in phosphoric acid of different concentrations at room temperature, (b) Acid doping level of FBI membranes as a function of the acid concentration at room temperature. Reprinted from Q. Li, R. He, R. W. Berg, H. A. Hjuler, N. J. Bjerrum, Water uptake and acid doping of polybenzimidazoles as electrolyte membranes for fuel cells. Solid State Ionics, 168 (2004) 177-185, Copyright (2004) with permission from Elsevier. 

C.H. Shen, L.C. Jheng, S.L.C. Hsu, J.T.W. Wang, Phosphoric acid-doped cross-linked porous polybenzimidazole membranes for proton exchange membrane fuel cells, J. Mater. Chem. 21 (39) (2011) 15660-15665. 

Jiao, K. and Li, X. (2010) A three-dimensional non-isothermal model of high temperature proton exchange membrane fuel cells with phosphoric acid doped polybenzimidazole membranes. Fuel Cells, 10, 351. 

Wang JT, Wainright J, Yu H, Litt M, Savinell RF (1995) A H2/O2 fuel cell using acid doped polybenzimidazole as polymer electrolyte. In Proceedings for the first international symposium on proton conducting membrane fuel cells 1. Electrochemical society, Chicago, IL... 

The proton conduction based on the phosphoric acid is the basis of HT-PEMFC Celanese technology [37], mostly referred to as phosphoric acid-doped PBI (polybenzimidazole) This membrane enables operation at temperatures as high as 180°C, without the need for external humidification. Heat dissipation at this temperature is much easier than at the 70-80°C operating temperature of fuel cell systems using standard PFSA membranes. The CO tolerance at 180°C is such that even 1 % CO leads to a minor loss of power density compared to that using the same membrane on pure hydrogen. The downside of this membrane is its low conductivity below 1(X)°C, making a cold start impossible, as well as the lower power density at its optimal temperature. 

Li QF, Jensen OJ (2008) Membranes for high temperature PEMFC based on acid-doped polybenzimidazoles. Membr Technol 2 61-96... 

Phosphoric acid-doped polybenzimidazole (PA-PBl) membrane is the most common type for HT-PEMFCs. It was also introduced in the catalyst layer as an ionomer to improve proton conductivity [8, 80-83]. Similar to die apphcation of Nafion ionomer in the catalyst layer, polybenzimidazole (PBl) solution was incorporated into the catalyst layer by an impregnation method (die electrode was soaked in a PBI solution), by a gluing method (the PBl membrane was coated by PBI solution), or by a brushing method (the PBl solution was brushed onto the electrode) [80]. 

Li Q, Hjuler HA, Bjerrum NJ. Phosphoric acid doped polybenzimidazole membranes Physicochemical characterization and fuel cell apphcations. J Appl Electrochem... 

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