Acid-base polymer membranes

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. 

We have established that at high temperatures and/or at low humidity, conventional PESA membranes will dehydrate and will result in low proton conductivity. In the past several years, great efforts have been made to develop polymer membranes that are capable of retaining high proton conductivity in anhydrous environments, while still possessing chemical and electrochemical stability at high temperatures. These membranes can be classified into three groups (1) modified PESA membranes, (2) alternative sulfonated polymers and their composite membranes, and (3) acid-base polymer membranes. 

Kerres, J., Ullrich, A., Meier, R and Haring, T. 1999. Synthesis and characterization of novel acid-base polymer blends for application in membrane fuel cells. Solid State Ionics 125 243-249. 

Membrane research is a rather diverse field, exploiting perfluorinated iono-mers, hydrocarbon and aromatic polymers, and acid-base polymer complexes. Polyether and polyketo polymers with statistically sulfonated phenylene groups such as sPEK, sPEEK, and sPEEKK or polymers on the basis of benzimidazole have been tested as well. Recent reviews on membrane synthesis and experimental characterization can be found in the literature. ... 

Paddison SJ (2003) Proton conduction mechanism at low degrees of hydration in sulfonic acid-based polymer electrolyte membranes. Ann Rev Mater Res 33 289-319 Rasten E, Hagen G, Tunold R (2003) Electrocatalysts in water electrolysis with solid polymer electrolyte. Electrochimica acta 48 3945-3952... 

S.J. Paddison. Proton conduction mechanisms at low degrees of hydration in sulfonic acid-based polymer electrol3de membranes. 

Y. Liu, Q. Yu, and Y. Wu. More studies on the sulfonated poly(phenyl-ene oxide)+iniidazole bronsted acid-base polymer electrolyte membrane. J. Phys. Chem. Solids, 68(2) 201-205, February 2007. 

Liu Y, Yu Q, Yuan J, Ma L, Wu Y. Bronsted acid-base polymer electrolyte membrane based on sulfonated poly(phenylene oxide) and imidazole. Eur Polym J 2006 42(9) 2199-203. 

Kerres et al., among others, developed the acid-base blend membranes from sulfonated polymers and aminated or other basic polymers [98] and concluded that the protonation of the basic groups is incomplete if the base is too weak [99]. Very recently, Frutsaert et al. [70] synthesized novel polymers for the development of high temperature PEMFC membranes comprising a blend of s-PEEK and a fluorinated copolymer bearing imidazole functions as pendant groups. The extensive work on intermediate temperature fuel cell membranes are well reviewed in Chap. 4 of this book including polybenzimidazole as the basic component and sulfonated and phosphonated ionomers of either nonfluorinated or partially fluorinated backbones as the acidic component. 

The scope of the reviewed R D work is limited to intermediate-T acid-base blend membranes prepared by mixing polybenzimidazoles and sulfonated or phosphonated acidic polymers. Other membrane types, where the acid-base concept was used to improve their relevant... 

Fig. 4.5 Acidic polymers used as macromolecular ionical cross-linkers in acid-base-blend membranes mentioned in this review...

Cui W, Kerres J (2001) Acid-base polymer blends and their application in membrane processes. US Patent 6,194,474... 

Proton-exchange membrane fuel cells (PEMFC)—use solid-polymer proton-conducting membrane electrolyte at temperatures generally ranging from ambient to 90°C. Today s technology primarily uses the trifluoromethanesulfonic-acid-based electrolyte membrane, such as DuPont s Nafion . 

High-temperature proton exchange membrane fuel cells (HT-PEM fuel cells), which use modified perfluorosulfonic acid (PFSA) polymers [1—3] or acid-base polymers as membranes [4—8], usually operate at temperatures from 90 to 200 °C with low or no humidity. The development of HT-PEM fuel cells has been pursued worldwide to solve some of the problems associated with current low-temperature PEM fuel cells (LT-PEM fuel cells, usually operated at <90 °C) these include sluggish electrode kinetics, low tolerance for contaminants (e.g. carbon monoxide (CO)), and complicated water and heat management [4,5]. However, operating a PEM fuel cell at >90 °C also accelerates degradation of the fuel cell components, especially the membranes and electrocatalysts [8]. 

Fu et al. [11] reported the acid-base blend membranes based on 2-amino-benzimidazole (basic polymer) and sulfonated poly(ether ether ketone) (SPEEK) (acidic polymer) for direct methanol fuel cells. A novel polymer, polysulfone-2-amide-benzimidazole (PSf-ABIm), using carboxylated polysulfone and 2-amino-benzimidazole was synthesized for this purpose. The blend membrane of SPEEK/PSf-ABIm showed high performance a s represented by Figure 1.12. The blend membrane with 3 wt% PSf-ABIm was evaluated continuously for 120 h and little or no decline in performance was found after 120 h. On the other hand, the Nafion 112 membrane standard was observed to have a decline in performance due to a much higher amount of methanol crossover. 

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