Particles in Nafion

H. Uchida, Y. Ueno, H. Hagihara, and M. Watanabe. Self-humidifying electrolyte membranes for fuel cells Preparation of highly dispersed Ti02 particles in Nafion 112. Journal of the Electrochemical Society 150, A57-A62 2003. 

M. Watanabe, H. Uchida and M. Emori, Polymer electrolyte membranes incorporated with nanometer-size particles of Pt and/or metal-oxides Experimental analysis of the self-humification and suppression of gas-crossover in fuel cell, J. Phys. Chem., B, 1998, 102, 3129-3137 M. Watanabe, H. Uchida, Y. Seki and M. Emori and P. Stonehart, Self-humidifying polymer electrolyte membranes for fuel cell, J. Electrochem. Soc., 1996, 143, 3847-3852 H. Uchida, Y. Mizuno and M. Watanabe, Suppression of methanol crossover in Pt-dispersed polymer electrolyte membrane for direct methanol fuel cell, Chem. Lett., 2000, 1268-1269 H. Uchida, Y. Ueno, H. Hagihara and M. Watanabe, Self-humidifying electrolyte membranes for fuel cells, preparation of highly dispersed Ti02 particles in Nafion 112, J. Electrochem. Soc., 2003, 150, A57-A62. 

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. ... 

Hagihara, H., Uchida, H., Watanabe, M. (2006) Preparation of highly dispersed Si02 and Pt particles in Nafion 112 for self-humidifying electrolyte membranes in fuel cells. Electrochimica Acta, 51, 3979-3985. 

Nafion films CdS and ZnS-CdS particles supported in Nafion films... 

It should be acknowledged that Risen utilized the concept of the ionic domains in ionomers (Nafion sulfonates, sulfonated linear polystyrene) as microreactors within which transition metal partides can be grown and utilized as catalysts (23-25). Transition metal (e.g. Rh, Ru, Pt, Ag) cations were sorbed by these ionomers from aqueous solutions and preferentially aggregated within the pre-existing clusters of fixed anions. Then, the ionomers were dehydrated, heated and reduced to the metallic state with Hg. Risen discussed the idea of utilizing ionomeric heterophasic morphology to tailor the size and size distributions of the incorporated metal particles. The affected particle sizes in Nafion were observed, by electron microscopy, to be in the range of 25-40 A, which indeed is of the established order of cluster sizes in the pre-modified ionomer. 

Interesting reactivity has recently been found in the use of Nafion/silica composite material [30]. Nafion resins are active in the acylation of anisole with acetyl chloride, but entrapping highly dispersed nanosized Nafion particles in a silica matrix leads to a much more active catalyst, as indicated in Table 5. 

The polymeric perfluorinated sulfonic acid has been used as a matrix for a system which combines semiconductor CdS crystallites and a Pt hydrogen-evolution catalyst In a photocatalytlc hydrogen generator (73-74). Upon photolysis of the platinized CdS particles In the presence of a sacrificial electron donor, Na.S, the production of hydrogen gas by water reduction was observed. The number of moles of produced with a typical NAFION/(MS system exceeds the moles of CdS present by a factor greater than 100. 

The analytical application of particle-dispersed-modified electrodes to the selective detection of a single analyte is limited because of broad catalytic activities thus their use as electrochemical detectors following chromatographic separation of carbohydrates is often suggested. Similar nonspecific catalytic PMEs consisting of electrocatalytic RUO2 particles and Ru(OH2)6 in Nafion have been shown to catalyze the oxidation of catechol and of alcohols, respectively these could presumably be used in place of the carbon paste Ru02-modified electrode developed for postseparation detection of carbohydrates and alcohols. Other electrocatalytic particle electrodes were prepared from lead dioxide in polypyrrole and CoPc entrapped behind a permselective cellulose acetate film. ... 

Special attention deserves Nafion layered membrane prepared by the LBL self assembly of polyelectrolytes [25, 167-171]. A high selectivity membrane was prepared by Tang et al. [25] by self-assembling multi-layer Pd nanoparticles onto Nafion, using poly(diallyl dimethylammonium chloride) (PDAC) for charging the Pd particles. A Nafion 112 membrane was immersed in a Pd/PDDA dispersion and then in a Nafion dispersion. The process was repeated five times to obtain a multilayer self-assembly Nafion composite that shows a small decrease in conductivity (from 112 mS.cm for Nafion 112 to 81 mS.cm for the composite). However, the reported methanol permeability was reduced by a factor 0.0085 (out of scale in Fig. 6.22), leading to k 85. This composite membrane, whose strucmre is depicted in Fig. 6.24, was not tested in a DMFC. 

XRD and SEM measurements were done in order to probe the types of the layers of the Ni particles in the Nafion. Fig. 3.1 shows the XRD results of the Nafion film and the Ni-doped film. Previous work (see [Paquette... 

Nicotera et al. investigated the behavior of water confined in recast NAFION and in NAFION-clay hybrids membranes using PFGSE NMR and spin—lattice relaxation time Tj, and concluded that the transport mechanism is influenced from the dimensions of the dispersed platelets and mainly from the type of nanocomposites formed upon mixing the clay particles with the polymer matrix. Compared to pure NAFION, the water uptake and the water diffusion of the hybrid membranes are increased, with the exception of the Kunipia-NAFION composite [83]. 

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