Nafion membranes conductivity

It is important to recognize that the conductivity of Nafion in alkaline media strongly depends on the pretreatment history of the membrane. Thus, higher conductivities result when the membranes are equilibrated in NaOH solutions rather than in KOH solutions [61,62], and better conductivity can be achieved with thinner, low EW membranes. It was also reported that the conductivity of the membranes is increased by soaking the membranes in water at high temperatures and at elevated pressures (Table 4.8.3 [63]). Table 4.8.4 describes the Nafion membrane conductivity data at various concentrations of HCl and NaOH [43]. 

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. 

The actually developed PEMFCs have a Nafion membrane, which partially fulfills these requirements, since its thermal stability is limited to 100 °C and its proton conductivity decreases strongly at higher temperatures because of its dehydration. On the other hand, it is not completely tight to liquid fuels (such as alcohols). This becomes more important as the membrane is thin (a few tens of micrometers). Furthermore, its actual cost is too high (more than 500 m ), so that its use in a PEMFC for an electric car is not cost competitive. 

The semipermeable Nafion membrane used to separate the anode and cathode compartments resists chemical attack. Its anionic side chains permit conduction of Na+, but not anions. The cathode compartment is loaded with pure water, and the anode compartment contains seawater from which Ca2+ and Mg2+ have been removed. Explain how the membrane allows NaOH to be formed free of NaCI. 

Ab initio methods provide elegant solutions to the problem of simulating proton diffusion and conduction with the vehicular and Grotthuss mechanism. Modeling of water and representative Nation clusters has been readily performed. Notable findings include the formation of a defect structure in the ordered liquid water cluster. The activation energy for the defect formation is similar to that for conduction of proton in Nafion membrane. Classical MD methods can only account for physical diffusion of proton but can create very realistic model... 

Pt/XC-72R catalyst mixture that was sprayed directly onto one of the graphite separator plates that came with the high-flow rate single-cell electrolysis cell. We have found that the copper(I) oxidation reaction does not require a catalyst (see below). Thus, a catalyst-free graphite separator plate was used as the anode. Nafion membranes were used as the electrolyte for H+ conduction. 

In a H2/air fuel cell, the protons produced at the anode side need to be transferred to the cathode side to react with 02. This requires a proton transport electrolyte. Nafion membranes, composed of a perfluorosulfonated polymer, are the most commonly used polymer electrolyte membranes to conduct protons. The structure of the Nafion membrane is shown in Figure 1.5. Nafion can take on a... 

The ionic resistance of a polymer electrolyte membrane is an important parameter in determining the mobility of protons through the membrane and the corresponding voltage loss across the membrane. Currently, the most commonly used membranes in PEM fuel cells are Nafion membranes produced by DuPont. However, these membranes are limited to low-temperature uses (usually below 80°C) because membrane dehydration at high temperatures can lead to reduced water content and then a lower proton transfer rate, resulting in a significant decrease in conductivity. The relationship between conductivity and the diffusion coefficient of protons can be expressed by the Nemst-Einstein equation ... 

Figure 5.16. Schematic illustration of a conductivity cell for Nafion membranes (1) graphite current collectors (2) carbon paper electrodes (3) membrane (4) electrical connections (5) beaker filled with deionized water and (6) thermocouple [15]. (Reprinted from Journal of Power Sources, 134, Silva RF, De Francesco M, Pozio A. Tangential and normal conductivities of Nafion membranes used in polymer electrolyte fuel cells, 18-26, 2004, with permission from Elsevier.)...

Silva RF, De Francesco M, Pozio A (2004) Tangential and normal conductivities of Nafion membranes used in polymer electrolyte fuel cells. JPower Sources 134 18-26... 

For the Nafion -based PEM fuel cells, the membrane conductivity decreased with increasing operating temperatures. The resistance points on the Re axis at the high-frequency end in Figure 6.49 can be treated approximately as the membrane through-plane resistance in PEM fuel cells other resistances, including the ionic resistance of the Nation ionomer and the cell contact resistance, may have made... 

Control over the course of the rearrangements of aryl esters can be achieved when the host matrix can interact with the ester and its intermediates through electrostatic or H-bonding interactions. Zeolites and Nafion membranes are two polymeric matrices in which such studies have been conducted. As mentioned above, the positions of the radical centers of the acyl radicals are known to be very near the oxygen atoms of their aryloxy partners at the moment of birth of the radical pairs from the excited singlet state of an aryl ester in all media all subsequent diffusion... 

The upper temperature at which polyelectrolytes can be utilised can be extended by substitution of a polar organic solvent for water in the electrolyte. Conductivities of up to 1 Q 1m 1 have been obtained for sulphonated PEEK using anhydrous pyrazole and imidazole at 200 C (Kreuer et al., 1998). Solvents used to form electrolytes in Nafion membranes have included alcohols, amines, propylene carbonate, dimethoxyethane, dimethyl form-amide, dimethyl sulphoxide and TV-methyl pyrrolidone. Typical conductivities for the latter three solvents are 10 to 1 O-lm 1 at room temperature, and the conductivity is thermally activated with activation energies in the range 9 to 24 kJ/mol (Doyle et al., 2001). 

The membrane and ionomer humidification requirements are of paramount importance for PEMFC operation since the proton conductivity is a fundamental necessity in the membrane as well as in the electrode for the fuel cell to function. The operating conditions of current PEMFCs are dictated by the properties of the membranes/ionomers. Now, the most important membrane type (e.g., Nafion membranes from DuPont) is based on PFSA ionomers that are used in the membrane... 

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