Polymer electrolyte fuel cell (PEFC) is expected to applications for various usages such as a power source for small robots and personal computers because PEFC has high energy density and can generate electric power under low temperature environment. As the application, swimming fish robots with PEFC are useful for various usages such as ecological investigation in water etc. In the case that rechargeable batteries are used for supplying electricity to robots, they are not able to continue swimming for a long time because of low energy density of the batteries. Therefore, a small and ultra-light passive-type polymer electrolyte fuel cell called "Power Tube" has been developed. On the basis of this fuel cell technology, the authors have created low energy consumption small fish robots powered by Power Tubes on a float or a buoy. The fish robot with a float swims for approximately 50 minutes by only Power Tubes with a voltage booster and the other fish robot with a submersible system can also swim for about 50 minutes by a hybrid system of a lithium polymer battery and Power Tubes.
