FIGURE 6 Schematic diagram of solid oxide cell, a high-efficiency, all-solid-state power generating device with about 50 percent efficiency.

The solid oxide cell is probably the only high-efficiency, all-solid-state power generating device (Figure 6). The key element is a yttria-zirconia alloy that conducts oxygen ions at 900°C. Gaseous fuel is applied to one side of the tube and air to the other. Oxygen ions migrate through the ceramic and react with the fuel, releasing electrons as they do so. The device thus generates power. It may reach about 50 percent efficiency, exceeding the 42 percent efficiency of a coal-fired plant.

In this area of technology there is a lot of room for research in ionic conduction in solids, and better conductors at lower temperatures would be a great help.

This discussion has focused on the near-term electric energy technologies. Obviously, there are many, more long-term developments, such as fusion, magnetohydrodynamic power, and geothermal power, where the limitations of present high-temperature materials are one of the principal barriers to progress—an area in which future materials research should be concentrated.

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