A fuel cell is equivalent to a generator: it converts a fuel's chemical energy directly into electricity. The main difference between these energy conversion devices is that the fuel cell acccomplishes this directly, without the two additional intermediate steps, heat release and mechanical motion.

A fuel cell has two basic elements: a fuel delivery system and an electro-chemical cell that converts the delivered fuel into useful electricity. It is this unique combination that enables fuel cells to potentially offer the best features of both heat engines and batteries. Like batteries, the cell generates a dc electric output and is quiet, clean, and shape-flexible, and may be manufactured using similar plate and film-rolling processes. By contrast, the fuel delivery system ensures that fuel cells, like heat engines, can be quickly refueled and operate for long periods between stoppages.

Figure 1. Timeline of major fuel cell milestones.

"Fuel cell...