Steel might replace expensive ceramics in fuel cells

FINLAND'S Technical Research Centre (VTT) is investigating new options to help make solid oxide fuel cells commercially viable as a clean source of distributed power generation. The VTT says reducing the operating temperature would allow the use of tough metallic components rather than brittle ceramics in the interconnectors.

In the VTT's tests, relatively cheap Finnish stainless steel performed well, promising good durability and low manufacturing costs for next-generation fuel cells.

Commercial applications of solid oxide fuel cells (SOFC) in distributed power generation have been slow to emerge due to high cost, gradually decreasing performance and limited lifespans.

While manufacturing costs can be expected to decrease with increasing production volumes, poor durability and short life add to the cost and much remains to be improved in the cells' critical parts, according to the VTT. These critical parts include the cell interconnectors, which until recently were mostly made of brittle ceramics.

New cell types can operate at lower temperatures (650-750°C), opening the possibility to use steel in the interconnectors,according to the VTT.

But even this temperature range is still sufficient to induce material degradation. Dedicated interconnector steels have been developed for stability and electrical performance in the operating environment, but certain standard steel types have also been applied for the purpose.

VTT has tested the performance of different interconnector steels for SOFC service in the actual operating environment with hydrogen fuel.

In these experiments, a Finnish ferritic steel grade performed surprisingly well in comparison with newer high-chromium steels from Japan and Germany.

For long-term service, further development may be necessary, but a satisfactory combination of alloy stability and electrical performance was achieved with a currently available alloy, the VTT claimed.

This result is promising and is expected to help in bringing the solid oxide fuel cells to commercial reality towards the end of the decade, according to the VTT. This would allow efficient production of distributed heat and power with almost no harmful emissions or noise.