Category: 10. Fuel-Cell Stack and System Design

A fuel cell is being considered for a manned space flight. Because hydrogen and oxygen are needed for propulsion power, these are the preferred fuel and oxidant. The basic cell performance is shown in Figure 10.20. Our job is to recommend the current density and voltage at which the fuel cell operates. A high current…

It might seem odd to include mechanical concerns in a text on electrochemical engineering. Experience has taught us that the mechanical design is critical in electrochemical systems. Many times performance difficulties can be traced to poor mechanical design or structural failure. Of course, mechanical engineering of materials is a large field in itself. Here our…

For any fuel cell system at steady operation, water must be balanced; that is, the amount of water entering the fuel-cell system plus the water produced by the reactions must equal the amount of water in the exhaust. Similarly, water must be in balance around each component of the system. Just as a water balance…

As was noted in Section 10.4, the fuel and oxidant must be directed over the surface of anode and cathode in the fuel-cell stack. Most often this is done with rectangular channels. The set of channels make up the flow field. Drawing on what we have learned in the previous sections, we now have a…

For both the fuel and oxidant streams, utilization is an important design factor. The utilization of fuel plays a key role in the fuel efficiency, and the utilization of the oxidant, typically air, affects the mechanical efficiency of the system and polarization losses in the cell. We’ll first consider the oxidant by examining the cathode of a…

Let’s now take a more detailed look at the components of a bipolar fuel-cell stack as illustrated in Figure 10.4. Multiple layers are assembled together to form a cell, and these layers are arranged like a deck of cards to form the stack. Starting from the center of the cell in Figure 10.4 and working out, the electrolyte…

Potentials of individual cells are about 1 V. Most applications require at least a few volts, but often hundreds of volts are desired. Single cells can be fabricated and then connected in series to increase the voltage, just as is done in batteries. The first approach, which is used commonly in batteries, is referred to as…

In this section, we consider the initial or basic design of the fuel-cell stack. The fuel-cell stack is part of the fuel-cell system, which itself is part of a larger system. Therefore, some of the important design specifications and constraints for the fuel-cell stack are derived from the high-level requirements of the larger system. For…

In contrast to the battery, a fuel cell is typically a steady-state device. As such, the fuel and oxidant are supplied continuously. In the previous chapter, we focused on the electrochemistry of the fuel cell. Now we will examine the entire fuel-cell system. Many cells are combined to form a cell stack assembly (CSA), which…