Fuel cell types

Figure 3.3. Electrode configuration for SEP (a) and for electrochemical promotion (or NEMCA) studies (b). The latter can be carried out using the fuel-cell type configuration (c) or the single chamber type configuration (d).

Figure 4.1. Electrode configuration for NEMCA studies using (a) the fuel cell type reactor and (b) the single-chamber type reactor.

Qualitatively similar behaviour for methanol oxidation on Pt/YSZ was reported by Cavalca, Larsen, Vayenas and Haller51 who used the single chamber design51 instead of the fuel-cell type design of the earlier study of Neophytides and Vayenas.50 Cavalca et al51 took advantage of the electrophobic... 

Figure B.l. (Top) Typical reactor designs used in electrochemical promotion studies singlechamber design (left) and fuel cell type design (right). (Bottom) Typical apparatus for electrochemical promotion studies using a three-pellet single chamber reactor.

This type of cell operates at the highest temperature (1000 °C) of all current fuel cell types. This high operating temperature has many advantages including producing steam suitable for co-generation, the ability to reform many fuels efficiently and the overall fast kinetics of the... 

Fuel cell type Electrolyte Operating Temperature CO... 

The dynamic behavior of fuel cells is of importance to insure the stable operation of the fuel cells under various operating conditions. Among a few different fuel cell types, the direct methanol fuel cell (DMFC) has been known to have advantages especially for portable... 

The situation changed drastically in the mid-1990s in view of the considerable advances made in the development of membrane hydrogen-oxygen (air) fuel cells, which could be put to good use for other types of fuel cells. At present, most work in methanol fuel cells utilizes the design and technical principles known from the membrane fuel cells. Both fuel-cell types use Pt-Ru catalyst at the anode and pure platinum catalyst at the cathode. The membranes are of the same type. 

Different fuel cell types exist. They operate at different temperatures and are generally distinguished by their electrolytes. The status of development differs widely for each type. Table 6.4 provides a comparison of the major types of fuel cells currently under development. 

Fuel Cell Type Electrolyte Temp., °C Efficiency, % Advantages Disadvantages Operation Field... 

Depending on the operating temperature and the complexity of the device some fuel cells types are better fit than others to small-scale residential applications (typically in the range from 30 kWe to 1 MWe), although all types of FCs have to be commercially viable at the small scale before they can be viable at the large scale. 

The technically relevant fuel cell types are shown in Fig. 13.5 a newer development of the PEM fuel cell is the direct-methanol fuel cell (DMFC), which uses a diluted... 

Table 13.2. Fuel gas composition requirements of different fuel-cell types...

Table 1-1 Summary of Major Differences of the Fuel Cell Types... 

The fuel cell types addressed in this handbook have significantly different operating regimes. As a result, their materials of construction, fabrication techniques, and system requirements differ. These distinctions result in individual advantages and disadvantages that govern the potential of the various cells to be used for different applications. 

The characteristics, advantages, and disadvantages summarized in the previous section form the basis for selection of the candidate fuel cell types to respond to a variety of application needs. 

Participants Application Size range Fuel /Fuel Cell type Nature of Activity... 

The above discussion implies that MCFCs should be operated at low reactant gas utilizations to maintain voltage levels, but doing this means inefficient fuel use. As with other fuel cell types, a compromise must be made to optimize overall performance. Typical utilizations are 75 to 85% of the fuel. 

For every molecule of hydrogen (H2) that reacts within a fuel cell, two electrons are liberated at the fuel cell anode. This is most easily seen in the PAFC and PEFC because of the simplicity of the anode (fuel) reaction, although the rule of two electrons per diatomic hydrogen molecule (H2) holds true for all fuel cell types. The solution also requires knowledge of the definition of an ampere (A) and an equivalence of electrons. 

Fuel Cell Type Location Status Start Date Operating Hours MWhrs Output Size, kw Design Actual Eff. % Avail. %... 

Year Customer Size, kWe Fuel Cell Type CeU Length (cm) Operating Hours Cell Number MWH (DC) Operating Hours... 

There are several types of fuel cells with different characteristics and uses. Fuel cells are usually classified according to the electrolyte that is used. Table 7.1 shows some common fuel cell types and their uses. 

The AFC is one of the oldest fuel cell types. The cell reactions are as follows (the existence of the peroxide intermediate H02 has been already discussed) ... 

Fuel Cells are taken up in Section 1, which begins with a brief overview of fuel cell fundamentals and a synopsis of each of the major fuel cell types. It then provides a review of lEA government work as it relates to each fuel cell type, including R D efforts directed as specific fuel cell types a review of programs undertaking basic fuel cell R D and, the section concludes with a review of fuel cell demonstrations for transportation and stationary applications. 

Direct methanol fuel cell technology is relatively new compared to that of fuel cells powered by pure hydrogen, and research and development are roughly 34 years behind that of other fuel cell types. Nonetheless, the DMFC appears to be the most promising as a battery replacement for portable applications such cellular phones and laptop computers, and a number of manufacturers are already introducing commercial versions of these applications. 

Although they are more resistant to impurities than other fuel cell types, scientists are looking for ways to make MCFCs resistant enough to impurities from coal, such as sulphur and particulates. 

Solid oxide fuel cells (SOFC) use a hard, non-porous ceramic compound as the electrolyte. Since the electrolyte is a solid, the cells do not have to be constructed in the plate-like configuration typical of other fuel cell types. SOFCs are expected to be around 50-60 percent efficient at converting fuel to electricity, however, calculations show that over 70 percent may be achievable. In applications designed to capture and utilize the system s waste heat (co-generation), overall fiiel use efficiencies could top 80-85 percent. 

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