Cation solid polymer electrolyte membrane

Table 1.7 Properties of commercial cation exchange (adapted from Smitha eta ., 2005). Reprinted from J Membrane Sci, 259, Smitha B, Sridhar S and Khan AA, Solid polymer electrolyte membranes for fuel cell applications - a review, page 13, Copyright (2005), with permission from Elsevier...

The idea of using an ion-conductive polymeric membrane as a gas-electron barrier in a fuel cell was first conceived by William T. Grubb, Jr. (General Electric Company) in 1955. - In his classic patent, Grubb described the use of Amber-plex C-1, a cation exchange polymer membrane from Rohm and Haas, to build a prototype H2-air PEM fuel cell (known in those days as a solid-polymer electrolyte fuel cell). Today, the most widely used membrane electrolyte is DuPont s Nation... 

The solid polymer electrolyte (SPE) fuel cell makes use of the high stability and the cation selectivity of Nafion, a Teflon-like material that has been modified by the incorporation of sulfonic groups. The membrane is coaled with a porous catalyst on both sides. Hydrogen is oxidized on one side of the membrane and the formed in the process is transported across the membrane to the other side, where it interacts with (OH) ions formed by the reduction of oxygen, to form water. This water is removed from the cell by capillary action with the use of a... 

Fig. 9 Solid polymer electrolyte (SPE) cell with cation exchanger membrane Nafion [13].

Ion-exchange membrane coated with porous catalyst metal (Solid Polymer Electrolyte, SPE) as well as GDE can provide gas phase electrolysis of CO2. The first attempt was published by Ito et al., communicating thin porous Au layer electrode coated on a cation exchange membrane. The SPE could not enhance the cathodic current of CO2 reduction.2" DeWulf et al. applied an SPE with Cu as the catalyst layer on a cation exchange membrane (CEM) Na-fion 115. The SPE reduced CO2 to CH4 and C2H4 for a while, but the current density for CO2 reduction dropped below 1 mA cm after 70 min electrolysis. " ... 

In recent years, many papers have reported the preparation of cation exchange membranes by this method to obtain solid polymer electrolytes for fuel cells. 

N. Mayo, R. Harth, U. Mor, D. Marouani, J. Hayon and A. Bettelheim, Electrochemical response to H2, 02, C02 and NH3 of a solid-state based on a cation- and anion-exchange membrane serving as a solid polymer electrolyte, Anal. Chim, Acta, 1995,310, 139-144. 

It is well known today that perhaps the most dramatic application of the fuel cell—an electrochemical device that may be based in the future upon the oxidation of aliphatic hydrocarbons— was in the Gemini Space Mission. In this application, the cell was based upon the use of a solid polymer electrolyte —a cation-exchange membrane in its acid form—but with hydrogen and oxygen as the fuels rather than an aliphatic hydrocarbon. Considerable research and development preceded and supported these successful missions and the units demonstrated that indeed the H2/O2 fuel cell was capable of extended performance at relatively high current densities—2l capability of fundamental importance in commercial applications. 

A particular approach adopted by General Electric In U.S.A. is the solid polymer electrolyte (SPE) cell in which the porous cloth-type separator is replaced by a polymeric ion exchange membrane which is conductive to cations (Figure 5). The particular membrane employed, NAFION, is a perfluorsulphonlc acid pol3nner which is extremely stable in both acid alkaline solution. Appropriate electrocatalysts are coated on each face of the polymer sheet and these are contacted by a metal mesh current collector. Further research is aimed at reducing the cost and improving the electrical efficiency of the system to make it competitive with conventional electrolyzers. 

Many solid electrolytes are known today and it can be expected that their importance will further increase, especially for electrochemical devices. For example, beta-alumina solid electrolyte (BASE) is a fast ion conductor, which is used as a membrane in electrochemical cells. It can contain small ions like sodium, which show a high mobility. More classical examples are electrolytes based on lithium or silver iodide where the small cations are very mobile [13]. Note that solid polymer electrolytes are also a rapidly growing field [14]. 

Solid polymer electrolytes on the basis of a polymer cation exchange membrane in H" -foim or an anion exchange polymer membrane in OH -form can be considered as quasi-aqueous electrolytes, whereby the water is absorbed in the phase separated ionic nano morphology of the respective material. This nano morphology forms imiic pathways through the polymeric membrane connecting the two fuel cell electrodes. 

Cation exchange resins are commonly used for polymer electrolyte membranes and DMFC applications as a separator. Usually, the sulfonic acid group qualifies it for use as a proton conductor and it was observed that it can also be useful as a separator and electrolyte in a supercapacitor. Park et al used an all-solid supercapacitor with an electrode containing RUO2 and a Nafion polymer as both separator membrane and electrolyte. The paste of RUO2 and Nafion was applied on carbon paper with a brush and hot-pressed with the Nafion membrane. The cyclic voltammetry was done in the voltage window of 0-1V. The specific capacitance was studied with varying concentrations of Nafion (50, 33, 15 and 7 wt%) in the... 

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