Direct methanol fuel cell membrane thickness

FIGURE 21.44 Methanol permeation rate of the membranes as a function of thickness and at different temperatures (a, a, o, ) commercial samples N112, N115, and N117 (b, bj, , ) composite membranes. Temperature at 25°C, plots a and b (open symbols), and at 65°C, plots a and bl (full symbols). (Reprinted from J. Electroanal. Chem., 532(1-2), Dimitrova, R, Friedrich, K.A., Vogt, B., and Stimming, U., Transport properties of ionomer composite membranes for direct methanol fuel cells, 75-83, Copyright 2002, with permission from Elsevier.)... 

Fig. 21 Water permeation from anode to cathode in the direct methanol fuel cell for radiation grafted membranes based on FEP with different initial film thickness (25 and 75 ixm) and Nafion 117. The electroosmotic drag coefficient H20/H is calculated from the slope of the regression line. Conditions cell temperature 90 °C, pressime 2 bar, 20mLmin 0.5 M methanol, air stoichiometry is 2.0 for FEP and 3.0 for Nafion 117...

Abstract There have been numerous studies on modifying DuPont s Nafion (a perfluorosulfonic acid polymer) in order to improve the performance of this membrane material in a direct methanol fuel cell. Modifications focused on making Nafion a better methanol barrier, without sacrificing proton conductivity, so that methanol crossover during fuel cell operation is minimized. In this chapter, a brief literature survey of such modifications is presented, along with recent experimental results (membrane properties and fuel cell performance curves) for (1) thick Nafion films, (2) Nafion blended with Teflon-FEP or Teflon-PFA, and (3) Nafion doped with polybenzimidazole. 

Fig. 14.2 The effect of membrane thickness on direct methanol fuel cell performance. T = 60°C, 1.0 M methanol feed, ambient pressure air at 500 seem, (circle) and (filled rectangle) Nafion 117 (215 pm wet thickness) (triangle) and (filled triangle) Nafion 112 (60 pm wet thickness)...

There has been considerable research on modifying Nafion, so as to improve its properties for use in a direct methanol fuel cell. In this chapter, a review of Nafion-based DMFC membranes is presented, including a literature survey followed by recent results by the present authors on improving Nafion by (1) using thick stacked Nafion membranes, (2) blending Nafion with Teflon-FEP or Teflon-PFA, and (3) doping Nafion with polybenzimidazole. 

These fluorinated PPPs led to original membranes endowed with a good thermal stability (films were stable in air up to 310 °C), interesting electrochemical properties, very low methanol crossover (its intrinsic permeability to methanol was lower than that of Nation for the same thickness), high ion exchange capacity (1.3 mequiv./g), and satisfactory conductivity (8.5 mS/cm) for a thickness of 40 pm. AU these relevant characteristics show that these membranes are potential candidates for direct methanol fuel cells [111b]. 

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