The sugar cube-sized SOFC
The sugar cube-sized SOFC
[Click to enlarge image]
The honeycomb-type SOFC
The honeycomb-type SOFC
[Click to enlarge image]

The National Institute of Advanced Industrial Science and Technology (AIST) developed an extremely small SOFC (solid-oxide fuel cell) that is operable at 550°C.

The size of the cylindrical cell was substantially downsized so as to increase the ratio of electrode area to volume. Despite the small size, the fuel cell features high power output.

Twenty five needle-like modules, each with a diameter of 0.8mm, are integrated to form a sugar cube-sized SOFC that can generate 3W of electricity (Fig 1). In another method, cells can be fit into an extrusion-molded honeycomb with a density of more than 250 cells/cm2 (Fig 2).

The product is intended for cogeneration applications and automotive APUs (auxiliary power unit). It will be exhibited in the NEDO's booth at the nano tech 2009 International Nanotechnology Exhibition and Conference, which will take place at Tokyo Big Site from Feb 18 to 20, 2009.

Compared with other fuel cells, SOFCs are characterized by their high efficiency. And they are appropriate for power generation and cogeneration. However, existing SOFCs are vulnerable to load change because of their high operating temperature ranging from 700 to 1,000°C. Therefore, PEFCs (polymer electrolyte fuel cell) have been believed to be superior to SOFCs for automotive use.

The prototyped module is so small that its heat capacity is low, resulting in low operating temperature. Also, the absolute value of thermal expansion is low, which means less thermal shock and quick activation.

It is actually activated in about five minutes, but "we feel that it is possible to activate it in less than a minute," said Masanobu Awano, group leader of the Functional Assembly Technology Group at the Advanced Manufacturing Research Institute of AIST.

At present, the fuel cell is intended for use by automotive APUs, whose load change is small But it can be used to provide power to fuel-cell vehicles if technology for effectively connecting multiple modules is established, according to AIST.