4125 Molten Carbonate Fuel Cell MCFC

Molten carbonate fuel cells, originally developed to operate directly from coal, operate at 600°C and require CO or CO2 on the cathode side and hydrogen on the anode. The cells use carbonate as the electrolyte. The electrical efficiency of these fuel cells is high at about 50%, but the excess heat can be used for cogeneration for improved efficiency. The high temperatures required make these fuel cells not particularly suitable for vehicular applications, but they can be used for stationary power generation.

4.1.2.6 Solid Oxide Fuel Cell (SOFC, ITSOFC)

Solid oxide fuel cells (SOFCs) use a solid ionic conductor as the electrolyte rather than a solution or a polymer, which reduces corrosion problems. However, to achieve adequate ionic conductivity in such a ceramic, the system must operate at very high temperatures. The original designs, using yttria-stabilized zirconia as the electrolyte, required temperatures as high as 1000°C to operate, but the search for materials capable of serving as the electrolyte at lower temperatures resulted in the "intermediate temperature solid oxide fuel cell" (ITSOFC). This fuel cell has high electrical efficiency of 50 to 60%, and residual heat can also be used for cogeneration. Although not a good choice for vehicle applications, it is at present the best option for stationary power generation.

The fuel cell features described above are summarized in Table 4.1. The usable energy and relative costs of various fuels used in fuel cells are listed in Table 4.2. The selection of fuel cells as the primary energy source in EVs and HEVs depends on a number of issues, ranging from fuel cell technology to infrastructure to support the system. Based on the discussion in this section, the choice of fuel cell for the vehicular application is an alkaline or proton exchange design, while for stationary applications, it will be the SOFC. The size, cost, efficiency, and start-up transient times of fuel cells are yet to be at an acceptable stage for EV and HEV applications. The complexity of the controller required for fuel cell operation is another aspect that needs further attention. Although its viability has been well-proven in the space program, as well as in prototype vehicles, its immature status makes it a longer-term enabling technology for an EV and HEV.

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