Nafion inclusion

Nafion inclusion, supramolecular assemblies and adsorption in thin mercury filmsSeveral works have focused in the determination of SCN or electroeat-alytic reduction of aldehydes and ketones , but the most important goal is towards the determination of CO2 in aqueous or gas phase. 

Recently, Dahr [1], Stonehart [2] and Watanabe [3] have made an attempt to reduce the humidification constraints in solid polymer electrolyte fuel cells (SPEFCs) by using modified perfluorosulfonic membranes. A recast Nafion film sandwiched between the two electrodes was first proposed by Dahr [1] for the realization of an internally humidified SPEFC. Stonehart [2] suggested the inclusion of small amounts of silica powder into the recast film in order to retain the electrochemically produeed water inside the membrane. Watanabe et al [3] have tried to exploit the H2/O2 crossover through the membrane to produce a chemical recombination to water on small Pt clusters inside the membrane. All of these membranes were operated with H2/O2 at 80°C and allowed the development of systems without assisted humidification or with near ambient humidification. 

The inclusion of the last two catalytic systems i.e. zeolites and Nafion-H into the superacid catalyst family is still controversial. 

Using this extended model they computed the radial dependence of the proton diffusion coefficient for a Nafion membrane pore at a hydration level of 6 H20/S03 with inclusion of the two different formulations for the shielding. The results are shown in Figure 12.12 and show that the Attard formulation for the screening parameter results in higher proton diffusion particularly in the center of the pore (i.e. more efficient screening of the sulfonate anions). By comparing it to the experimental diffusion coefficient (6.0 X 10 ° the authors estimated that the hydrated protons reside... 

Figure 12.12. Variation of the diffusion coefficient as a function of the distance (p) from the center of the pore (i.e. p = 0 A) to within 1 A of the -SOs groups. The calculation is for Nafion with 6 H2O/ SOs" with inclusion of either Debye-Huckel or Attard models for the shielding. At the center of the pore the Attard formulation results in the most significant screening of the sulfonate groups and hence the higher proton self-diffusion coefficient.

As for most of the other advanced systems, these new protonic gel-type membranes appear to be still under evaluation. Presently, Nafion and related membranes still dominate the fuel cell market. The limited length of this chapter and its focus on batteries does not allow inclusion of a description of the present status of the polymer electrolyte fuel cells. The interested reader is referred to the many books and review articles available on the subject [e.g., 113,126,127]. 

W. Jong et al. modelled, fabricated and tested an IPMC strip actuator for inclusion into a low cost active tip bending system for a catheterscope [22]. Platinized Nafion 117 membranes with thicknesses of 170 pm were employed. The authors studied the force generated by the IPMC actuators and found that additional force may be required in order to overcome bending resistance from the catheterscope sheathing, capillary forces of attraction within wet ducts and viscous fluids. Encapsulation of the design was suggested to avoid gas production from hydrolysis [22]. 

The vaporization exchange model for water sorption and flux in Nafion-type PEMs has been modified and applied to treat transient water flux data (Rinaldo et al., 2011). A decisive modification was the inclusion of transport coefficients that depend on the water concentration or water content in the PEM. A simple form of this dependence is a step function change from slow to fast transport at a given transition concentration c. For this purpose, a hyperbolic tangent function was introduced ... 

Early reports and patent applications of Stonehart and Watanabe [22], Antonucci et al. [23], and Antonucci and Arico [24] claim the advantage of the introduction of small amounts of sihca particles to Nafion to ino-ease the retention of water and improve the membrane performance above 100°C. The effect is believed to be a result of water adsorption on the oxide surface. As a consequence the back-diffusion of the cathode-produced water is enhanced and the water electro-osmotic drag from anode to cathode is reduced [3]. A recent report of the group of Arico et al. [25] confirms the effect of water retention with the inclusion of oxide particles in Nafion and the importance of the acidity of the particle surface. An increase in both strength and amount of add surface functional groups in the fillers enhances the water retention in the membrane SiO -PWA (modified with phosphotungstic acid) > SiOj > neutral-AljOj > basic-AI2O3 > ZrO. ... 

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