MHI, earlier this year, delivered solid polymer electrolyte fuel cells (PEFC)to the independent administrative institution, the Japan Marine Science and Technology Center (Below, JAMSTEC)for use as the main motive power for the "Urashima", an unmanned Autonomous Underwater Vehicle. On the 28th of February, a cruising test, beginning from Suruga Bay, was carried out that included a continuous cruise of 317km in length thus setting a world record *1.

This Autonomous Underwater Vehicle, the Urashima, is designed to carry out wide-ranging explorations of the deep floors of the ocean so that the ability to carry out long distance cruising was required. Such cruising ability exceeds the capacity of engines, storage batteries and other motive power sources used in the past. A new source of power with high efficiency and high output density was required. MHI, together with JAMSTEC, choose PEFC for the motive power source for this application because of its high power generating efficiency exceeding 50% and because, in recent years, commercial testing indicated that PEFC technology was nearing the level required for practical use.

However, the commercially available PEFC products were being used for land-based, fixed location, open exhaust related application environments. Compared to this, for use in the Urashima, the PEFC was required to operate successfully at low temperatures near 0°C, and in deep waters, exposed to water pressure and in a closed system. For these reasons, the requirements related to the fuel supply system, maintenance of running temperatures and high performance in a sealed pressure system were special problems that did not occur in the case of existing commercial products.

To deal with these problems, many new types of technology had to be developed and applied. In the case of the PEFC used for the Urashima were "separator-type" *2 design-type cells. To handle the high-pressure seal requirement, steel was used instead of carbon materials. In addition, a fuel supply system was developed that made it possible to make use of exhaust heat from power generation even in deep water and a stable system was developed that assured stable operation of the PEFC. Further, the system made it possible to use 100 percent of the fuel supplied for power generation with the only substance emitted by the system being water, a system that can be used in a sealed space.

The Urashima, equipped with these newly developed PEFC was able to carry out a 230km continuous cruise in December of last year. However, in the case of the more recent test cruise *3, the Urashima was able to extend the distance even further to 56 hours and 317km, a new world's record.

With this success as another step forward, it is now the goal to raise the reliability level of the system even higher, complete commercialization and achieve wide use of the system.

*1		The previous record was held by the English Southampton Marine research Institute that used primary manganese alkali batteries for its motive source and achieved a distance of 262km for its unmanned cruise vehicle.
*2		The PEFC generating cells consist of layered solid polymer electrolyte membranes and electrodes. The “separators” lie between the cell layers so as to produce electric current.   At the same time, to promote the flow of fuel and air (oxygen) to the cell surfaces, the separators are grooved. For the fuel, carbon is used because of its conductivity, workability, and resistance to corrosion.
*3		From 7:10am on February 26 th , the Urashima cruised around a fixed course in the center of Suruga Bay. The Urashima cruised around set course consisting of a 25 kilometer long arm running north to south, and an arm 25km long running east to west at a depth of 800m, proceeding and returning around two fixed points until 3:10pm on the 28 th , a period of 56 continuous hours of cruising.

(Output)

4kW [2kW2 units] (Operating temperature) 60°C (Power generation efficiency) 54% (Fuel used) Pure hydrogen/pure oxygen