SPE cell

Materials similar to Nation containing immobilized —COO- or —NR3+ groups on a perfluorinated skeleton were also synthesized. These are available in the form of solid membranes or solutions in organic solvents the former can readily be used as solid electrolytes in the so called solid polymer electrolyte (SPE) cells, the latter are suitable for preparing ion-exchange polymeric films on electrodes simply by evaporating the polymer solution in a suitable solvent. 

The average conditions extracted from Figure 7.17 are summarized in Table 7.2. Overall, actual alkaline electrolysis requires an energy consumption of 4.0-4.9 kW hm of H2. Consumption somewhat lower than 4.0kWhm has recently been claimed for SPE cells [73]. The current yield and H2 purity are seen to be close to 100% in alkaline electrolysis. 

The structure of a SPE cell is shown in Fig. 2.3. The basic unit of a SPE electrolyzer is an electrode membrane electrode (EME) structure that consists of the polymer membrane coated on either side with layers (typically several microns thick) of suitable catalyst materials acting as electrodes [43,49,50], with an electrolyzer module consisting of several such cells connected in series. The polymer membrane is highly acidic and hence acid resistant materials must be used in the structure fabrication noble metals like Pt, Ir, Rh, Ru or their oxides or alloys are generally used as electrode materials. Generally Pt and other noble metal alloys are used as cathodes, and Ir, Ir02, Rh, Pt, Rh-Pt, Pt-Ru etc. are used as anodes [43,46]. The EME is pressed from either side by porous, gas permeable plates that provide support to the EME and ensure... 

Electrochemical gas detection instruments have been developed which use a hydrated solid polymer electrolyte sensor cell to measure the concentration of specific gases, such as CO, in ambient air. These instruments are a spin-off of GE aerospace fuel cell technology. Since no liquid electrolyte is used, time-related problems associated with liquid electrolytes such as corrosion or containment are avoided. This paper describes the technical characteristics of the hydrated SPE cell as well as recent developments made to further improve the performance and extend the scope of applications. These recent advances include development of NO and NO2 sensor cells, and cells in which the air sample is transported by diffusion rather than a pump mechanism. 

The most convenient and reliable electrical biasing method for use with a hydrated SPE cell has been shown to be a three electrode potentiostatic circuit which maintains the sensing electrode at a predetermined potential vs. a stable reference (1 >3.>j0e The most reversible reference is a Pt/Hp, H+, static or dynamic. In practical instruments, however, good accuracy and convenience are achieved using a large surface area platinoid metal black/air (Op). All work reported in this study utilized the air reference which has a potential of approximately +1.05 V vs. a standard hydrogen electrode (SHE). For convenience, all potentials reported are vs. the SHE ... 

Response Time. The response-time curve for oxidation of CO with an SPE sensor cell having a platinoid sensing electrode is shown in Figure 8. Similar curves for the oxidation of N0 and reduction of N02 with an SPE cell having a graphite sensing electrode are also shown in Figure 8. All measurements were made at 25°C at gas flow of 60 cc/min. The current-time response can be estimated from the relationship... 

The other objective of the program is to reduce the manufacturing cost of the SPE cells for commercial application by a factor of about 14 1 from the cost of those used in the space and submarine systems. 

The methoxylation of A-ethyl carboxamides has been studied especially intensively, as the produced A-(a-methoxyethyl)amides may be transformed to the technically interesting vinyl amides by methanol elimination [209]. Glassy carbon anodes together with graphite or steel cathodes and tetramethylammonium methyl sulfate as conducting salt proved to be the best conditions. Alternatively, the SPE cell using Nafion as polyelectrolyte is practicable [218,219]. 

Another design that is used in chlo-ralkali electrolysis, water electrolysis, and electro-organic synthesis [95-97] is the solid polymer electrolyte (SPE) cell, where an ion exchanger membrane, for example, Nafion , serves as the electrolyte, Fig. 9. The microporous catalytic reaction layers are pressed directly onto the membrane with porous current collectors allowing transport of dissolved reactants and gaseous products into and out of the reaction layer. 

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

Among the exotic cells for the laboratory, flow cells (filter press cells) require an external loop with a pump to recirculate the electrolyte. Also, solid polymer electrode (SPE) cells have been described.16-19 The electrode material is deposited on both sides of a membrane (Nafion) or pressed against the membrane. An advantage is that the ionic conduction takes place in the membrane so that no supporting electrolyte is required. Moreover, this cell can work with gaseous reactants. 

The concept of using an ion-exchange membrane as an electrolyte in electrochemical cells was first introduced by Grubb in 1959. Since then, extensive research and development programs have been undertaken by the General Electric Company and others,resulting in the present solid polymer electrolyte (SPE) cells in which Nafion serves as the sole electrolyte as well as separator. High voltaic efficiency can be achieved in SPE cells because of the minimum contact resistance between electrode and separator. 

In SPE cells, electrocatalyst particles are bonded to the membrane surfaces. It is important to mention that good bonding... 

In the solid polymer electrolyte (SPE) cell process, the membrane and the electrode are bonded together, and it is difficult to reduce the boundary layer thickness on both surfaces of the membrane. This process also requires very thin electrodes which must be made highly porous without increasing their ohmic resistance or reducing their mechanical strength. 

The optimum current density of the membrane process (including the SPE cell process) is higher than that of the diaphragm process, because of the relatively high cost of the perfluoro ionomer membrane and its greater sensitivity to impurities, which requires the use of more expensive material for equipment. 

Figure 1. Electron micrograph of a new SPE cell, RuOx/SPE Interface (14).

During the fuel cell reaction, the electrochemical reaction taking place at the cathode of an SPE cell is... 

Nafion-315 is currently used in the SPE cell for brine electrolysis. The SPE electrolyzer exhibits a 15-20% energy savings when compared to conventional brine electrolyzers, primarily due to the decrease in ohmic and cathode overvoltages. Figure 5 shows the schematic of the SPE electrolyzer along with a typical membrane electrolyzer. The current distribution across the membrane of an SPE electrolyzer is more uniform than that of a typical brine electrolyzer. 

Development of Alternative Membranes. Nafion membranes show considerable promise with respect to their performance characteristics, low resistivity and long-term stability. However, the present cost (about 30/ft ) of Nafion membranes is rather expensive for the SPE cell to be cost-effective for industrial and utility applications. TJje ultimate goal is to reduce the membrane cost to about 3/ft. Alternative membranes have been evaluated for use in the SPE cell. Only fluorocarbon membranes have been considered in this application (10), since the cell environment is corrosive, and cell tempperature is high (from 80°C to 150°C). <, 3, 3 - trifluorostyrene-sulfonic acid... 

A recent study has shown that (58) membranes with carboxylic acid groups cannot be used without alkaline supporting electrolyte because of low swelling and poor conductivity in pure water. It is clear that the alternate membrane for the SPE cell should be a perfluorinated sulfonic acid membrane. To date (1981), Nafion still retains its uniqueness for this electrochemical application. 

The hydrated Nafion membrane currently used in SPE cells provides a highly acidic environment, equivalent to a 10 wt% H SOif solution (13). Thus, noble metals or noble metal oxides have to be used as electrocatalysts. It is of particular interest to develop an anion exchange membrane which will transport hydroxyl ions under water electrolysis or fuel cell conditions. This implies that the cell environment would be alkaline, which would enable the substitution of these expensive... 

Figure 12.7 Scheme of an SPE cell with cation-exchange membranes. 

SPE cell with cathode depolarized by oxygen is considered to give the best features [8,9,12,15,17]. Graphite activated by mixture, containing the oxides of ruthenium, iridium, and titanium, serve as an a ode. Mixture, containing 10 g of catalyst is required per 1 m of anode. Cathode contains plati-mxn black. 

In the Solid Polymer Electrolyte (SPE) cell , the electrodes do not pre-exist they are made by deposition onto the separator (Fig. 32.2b). 

A.B. LaConti, Introducticm to SPE Cell Technology, Proceedings, Oronzio DeNora Symposium Chlorine Technology, Venice (1979), p. 94. 

The third concept is called the SPE cell (Fig. 9.4c). The term SPE stands for Sohd Polymer Electrolyte. In such cells, ions which convey electric... 

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