Nafion conductivity

MECHANISTIC ASPECTS OF PROTON CONDUCTIVITY (NAFION AND PERFLUORINATED SULFONIC ACIDS)... 

Another option is the replacement of carbon as electronic conducting carrier material and the proton-conducting Nafion in the electrode layer as well by a conducting polymer, by which an improvement of the interfacial properties was expected [83]. The manufacture of a Pt/Ru-polymer nanocomposite was successfully carried out and first samples were tested in a DMFC. As electronically conducting polymers, poly(N-vinyl-carbazole) and poly(9-(4-vinyl-phenyl)-carbazole were... 

A newly-designed photoelectrocatalytic (PEC) reactor for CO2 reduction, which combines photocatalysis by Ti02 and electrocatalysis by carbon nanotubes (CNT), has recently been proposed (Fig. 7) [152]. A proton-conductive Nafion membrane connects the Ti02 and CNT. Irradiation of the combined system of nano-structured Ti02 deposited on a metal Ti electrode with Pt modified CNT deposited on carbon sheet caused water splitting to H2 and O2. A half-cell for the cathodic electrode, i.e., Pt or Fe modified CNT electrode, produces various organic molecules such as 2-propanol due to electrocatalytic reduction of CO2 on the electrode. The proposed PEC reactor is incomplete in its present state. However, these systems are expected to couple water splitting and CO2 reduction, and thus it may establish a new artificial photosynthetic system. 

Although having high chemical stability and proton conductivity, Nafion is expensive and has technical limitations ... 

More interesting results were obtained by Xiao et al. [200] using the PPA sol- gel process shown in Fig. 6.11. This procedure leads to very high acid doping levels (2a > 10-20), never reached by PBl membranes prepared with standard casting procedures. The conductivity of a membrane prepared with the PA A sol-gel method and 2a 16, raises from 15 mS.cm at 20 °C up to 270 mS.cm at 200 °C. The last value is comparable with those observed for the best proton conducting Nafion/inorganic composite membranes at temperatures above 100 °C. 

Lin Y, Yen C, Ma CM, Liao S, Lee C, Hsiao Y, Lin H (2007) High proton-conducting Nafion/-S03H functionalized mesoporous silica composite membranes. J Power Sources 171 388-395... 

Park YS, Yamazaki Y (2005) Low methanol permeable and high proton-conducting Nafion/ calcium phosphate composite membrane for DMFC. Solid State Ion 176 1079-1089... 

Skou E, Kauranen P, Hentschel J (1997) Water and methanol uptake in proton conducting Nafion membranes. Solid State Ion 97 333-337... 

Proton conducting Nafion-poly(l-vinyl-1,2,4-triazole) blends have been prepared by a film casting technique from solutions of the mixed polymers [97]. The methanol permeability is lower than the methanol permeability of pristine Nation 12. The electrical conductivity of the blend increases three orders of magnitude upon hydration. 

Conductivity. Nafion membrane behaves as an insulator when dry. However, it becomes conductive when hydrated, absorbing six molecules of water for each SOj" group in it. The conductivity of the H+ form of a membrane is an inherent characteristic that stems from the strong acidic groups present in the membrane. Its high intrinsic conductivity, coupled with its hydrophobicity, make Nafion a solid electrolyte. Hence, it replaces the conventional electrolyte in several electrochemical applications. 

L. Ghassemzadeh, G. Pace, V. Di Noto, K. MueUer, Effect of Si02 on the dynamics of proton conducting NAFION/(Si02)x composite membranes a solid-state F NMR study, Phys. Chem. Chem. Phys. 13 (2011) 9327-9334. 

Deposition of condncting polymers can be accomplished by either direct or feedback modes of SECM. In an earlier study, SECM was used to deposit polyaniline on a Pt substrate by scanning a UME tip in thin, ionically conductive Nafion films coated on the Pt surface (127). Anilinium ions were incorporated into Nafion films and the Pt substrate was biased positively, which caused the electropolymerization of aniline. The resolution of the polyaniline deposition is controlled by the tip size, the thickness of Nafion films, and the electric field distribution. 

FIGURE 5.21 Arrhenius plot showing temperature dependence of membrane conductivity. Nafion 117 membrane temperature range 25-90 °C water content in the membrane A = Nh,o/Nso3H = 22 [69]. 

Nation is a perfluorosulfonated ion-exchange polymer and has received a great deal of attention as a modifier for polymer-coated electrodes mainly because of its outstanding chemical stability and excellent ionic conductivity. Nafion-coated electrodes have been proved to be effective for the determination of electroactive compounds " . The attractive features of Nafion which are useful for electroanalytical purposes are its preconcentrating ability sof cations and its ionic selectivity. 

At present, the most commonly used humidified perfluorinated ionomer membranes, represented by Nafion, are limited to being used at temperatures lower than 100 °C because of the evaporation of water, which results in a rapid loss of conductivity. Nafion membranes are limited for practical application due to their high cost and high fuel crossover (Adjemian et al, 2002). 

Later, Du Pont in America developed its own ionically conducting membrane, mainly for large-scale electrolysis of sodium chloride to manufacture chlorine, Nafion , (the US Navy also used it on board submarines to generate oxygen by electrolysis of water), while Dow Chemical, also in America, developed its own even more efficient version in the 1980s, while another version will be described below in connection with fuel cells. Meanwhile, Fenton et al. (1973) discovered the first of a... 

Today, the term solid electrolyte or fast ionic conductor or, sometimes, superionic conductor is used to describe solid materials whose conductivity is wholly due to ionic displacement. Mixed conductors exhibit both ionic and electronic conductivity. Solid electrolytes range from hard, refractory materials, such as 8 mol% Y2C>3-stabilized Zr02(YSZ) or sodium fT-AbCb (NaAluOn), to soft proton-exchange polymeric membranes such as Du Pont s Nafion and include compounds that are stoichiometric (Agl), non-stoichiometric (sodium J3"-A12C>3) or doped (YSZ). The preparation, properties, and some applications of solid electrolytes have been discussed in a number of books2 5 and reviews.6,7 The main commercial application of solid electrolytes is in gas sensors.8,9 Another emerging application is in solid oxide fuel cells.4,5,1, n... 

This study, in conjunction with that discussed in 12.2.1.2, show that when using aqueous electrolytes or Nafion saturated with H20, the induction of NEMCA on finely dispersed noble metal catalysts is rather straightforward. The role of the electronically conducting porous C support is only to conduct electrons and to support the finely dispersed catalyst. The promoting species can reach the active catalyst via the electrolyte or via the aqueous film without having to migrate on the surface of the support, as is the case when using ceramic solid electrolytes. 

Stable highly conductive films of PPy-Nafion-impregnated Gore-tex and PPy-Nafion have also been reported. Polymer blends can also be produced by... 

When considering the morphology of prepared electro-catalysts are different to each other especially to the commercial one, one can think that the structure of electrode which was optimized to the commercial catalyst may not be optimum. So, the for the better electrode structures was conducted by investigating the effect of NFP. Fig. 2 is a schematic of electrode which depicts the effect of Nafion content[9]. For the conventional electrocatalysts, the range of 30 35 % NFP is reported as optimum value[10]. 

But when the contents of Nafion ionomer was increased from 30 to 45 % to find out the better electrode structures, the Pt-Ru/SRaw, which had showed the lowest single cell performance, became the best electro-catalyst. By this result one can conclude that as long as the structure of the electrode can be optimized for the each of new electro-catalysts, the active metal size is a more important design parameter rather than inter-metal distances. Furthermore, when the electro-catalysts are designed, the principal parameters should be determined in the consideration of the electrode structures which affect on the electron conduction, gas permeability, proton conductivity, and so on. 

A considerable decrease in platinum consumption without performance loss was attained when a certain amount (30 to 40% by mass) of the proton-conducting polymer was introduced into the catalytically active layer of the electrode. To this end a mixture of platinized carbon black and a solution of (low-equivalent-weight ionomeric ) Nafion is homogenized by ultrasonic treatment, applied to the diffusion layer, and freed of its solvent by exposure to a temperature of about 100°C. The part of the catalyst s surface area that is in contact with the electrolyte (which in the case of solid electrolytes is always quite small) increases considerably, due to the ionomer present in the active layer. 

Electrolytes for Electrochromic Devices Liquids are generally used as electrolytes in electrochemical research, but they are not well suited for practical devices (such as electrochromic displays, fuel cells, etc.) because of problems with evaporation and leakage. For this reason, solid electrolytes with single-ion conductivity are commonly used (e.g., Nafion membranes with proton conductivity. In contrast to fuel cells in electrochromic devices, current densities are much lower, so for the latter application, a high conductivity value is not a necessary requirement for the electrolyte. 

Implementation of Pt/C catalysts in PEFC technology using recast Nafion as a proton conducting and bonding agent [Raistrick, 1986 Wilson and Gottesfeld, 1992]. 

Figure 15.3 Simulated effectiveness factor for porous carbon electrode as a function of the exchange current density jo and DCo for Ip] = 0.4 V for a 10wt% Pt/C catalyst layer with 7= 10, A = 140m g p = 2gcm, Nafion volume fraction 0.6, thickness p,m, and ionic conductivity 0.05 Scm See the text for details. (Reproduced from Gloaguen et al. [1994], with kind permission from Springer Science and Business Media.)...

B. Fabre, S. Burlet, R. Cespuglio, and G. Bidan, Voltammetric detection of NO in the rat brain with an electronic conducting polymer and Nafion bilayer-coated carbon fibre electrode. J. Electroanal. Chem. 426, 75-83 (1997). 

Yoon el al. [112] reported an all-solid-state sensor for blood analysis. The sensor consists of a set of ion-selective membranes for the measurement of H+, K+, Na+, Ca2+, and Cl. The metal electrodes were patterned on a ceramic substrate and covered with a layer of solvent-processible polyurethane (PU) membrane. However, the pH measurement was reported to suffer severe unstable drift due to the permeation of water vapor and carbon dioxide through the membrane to the membrane-electrode interface. For conducting polymer-modified electrodes, the adhesion of conducting polymer to the membrane has been improved by introducing an adhesion layer. For example, polypyrrole (PPy) to membrane adhesion is improved by using an adhesion layer, such as Nafion [60] or a composite of PPy and Nafion [117],... 

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