Electrolytic cell module

Click Coached Problems for a self-study module on electrolytic cells. 

The Rolls-Royce fuel cell modules and stacks are devoid of compliant features, as the cross-section in Figure 4.3 shows, unless one counts the gap as compliant. Cell improvement is clearly possible via thin (say 6 p.m) electrolyte layers, as employed in a planar IT/SOFC by Global Thermoelectric (Section 4.9) and Steele etal. (2000a, b). Alternatively, modern reduced temperature electrolytes could be used. 

But another important complication is related to a not uniform distribution of humidity inside the electrolyte and on the catalyzed electrodes, and to the eventuality of incipient flooding phenomena, due to an excess of water bulked inside the fuel cell module that could dangerously limit the reactant entrance to active sites of catalyzed electrodes. This phenomenon could be present also without external water addition, because dry air streams entering into the ceU module gradually moisturize creating the possibility of local flooding at the end of their path [28]. 

The demonstrated cycle life of eight-cell modules has reached 400-640 cycles. The most serious failure mode seems to be the electrode warpage. The potential longevity of the system (stability of the electrolyte has been demonstrated in over 1200 cycles) can only be realized after methods of warpage control have been developed. 

The Electricity Council Research Centre has developed a 960-cell (40 modules of 24 tubular electrolyte cells each), 50 kW-hr, 100-V traction battery. The modules are shown in Figure 4. The battery was rated at 15.5 kW of average power, 29 kW of peak power, and weighed 800 kg. The specific peak power and specific energy are therefore 36 W/kg and 63 W-hr/kg, respectively. 

The first SC-SOFC stack with a serial connection of electrolyte-supported single cells delivered an OCV of 3 V [54]. An electrolyte-supported SC-SOFC miniature cell module consisting of two cells connected in series dehvered an OCV of 1.6 V at 500°C and a power density of 4.5 mW at 575 °C in a propane-air gas mixture R = 0.56) [55]. 

F ST Soltd-polymer electrolyte cells Tor water electrolysis, (a) Reactions, (b) The cell arrangement, (c) A demonstration eleccrolyser module which incorporates 34 cells and will generate up to 14 h of hydrogen. (Courtesy CJB Developments Ltd.)... 

Ffig. 5J Module voltage as a function of lime for a solid-polymer electrolyte cell stack (cf. Fig. 5.7)l Each module consists of 14 cathodes, each of area 0.093 m operating at 1.075 A cm and 55 C. 

Fuel cells are classified by the types of electrolytes used in the fuel cell module. Four distinct types of fuel cells have demonstrated remarkable performance capabilities as high-power sources. The most prominent fuel cell types are as follows ... 

Typical dimensions for the /5-alumina electrolyte tube are 380 mm long, with an outer diameter of 28 mm, and a wall thickness of 1.5 mm. A typical battery for automotive power might contain 980 of such cells (20 modules each of 49 cells) and have an open-circuit voltage of lOOV. Capacity exceeds. 50 kWh. The cells operate at an optimum temperature of 300-350°C (to ensure that the sodium polysulfides remain molten and that the /5-alumina solid electrolyte has an adequate Na" " ion conductivity). This means that the cells must be thermally insulated to reduce wasteful loss of heat atjd to maintain the electrodes molten even when not in operation. Such a system is about one-fifth of the weight of an equivalent lead-acid traction battery and has a similar life ( 1000 cycles). 

It is so universally applied that it may be found in combination with metal oxide cathodes (e.g., HgO, AgO, NiOOH, Mn02), with catalytically active oxygen electrodes, and with inert cathodes using aqueous halide or ferricyanide solutions as active materials ("zinc-flow" or "redox" batteries). The cell (battery) sizes vary from small button cells for hearing aids or watches up to kilowatt-hour modules for electric vehicles (electrotraction). Primary and storage batteries exist in all categories except that of flow-batteries, where only storage types are found. Acidic, neutral, and alkaline electrolytes are used as well. The (simplified) half-cell reaction for the zinc electrode is the same in all electrolytes ... 

Microwave power and its effect on the electrode/electrolyte interface, 439 Microwave region, Hall experiments, 453 Microwave spectroscopy, intensity modulated photo currents, 508 Microwave transients for nano crystalline desensitized cells, 514 Microwave transmission, as a function of magnetic field, 515 Minority carriers... 

The prototype DSCs used liquid electrolytes, typically L/I2 in an organic solvent such as propylene carbonate. The electron generation/collection problem in this cell has been discussed analytically with the help of intensity-modulated photocurrent and photovoltage spectroscopy [314]. A particularly challenging issue has been the replacement of the liquid electrolyte with a solid charge-transport material... 

Apart from recapture of the injected electrons by the oxidized dye, there are additional loss channels in dye-sensitized solar cells, which involve reduction of triiodide ions in the electrolyte, resulting in dark currents. The Ti02 layer is an interconnected network of nanoparticles with a porous structure. The functionalized dyes penetrate through the porous network and adsorb over Ti02 the surface. However, if the pore size is too small for the dye to penetrate, that part of the surface may still be exposed to the redox mediator whose size is smaller than the dye. Under these circumstances, the redox mediator can collect the injected electron from the Ti02 conduction band, resulting in a dark current (Equation (6)), which can be measured from intensity-modulated experiments and the dark current of the photovoltaic cell. Such dark currents reduce the maximum cell voltage obtainable, and thereby the total efficiency. 

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