Challenges to obtaining high efficiency in solid oxide fuel cells

Efficient conversion of hydrocarbon fuels to electricity is the main motivation for development of solid oxide fuel cells (SOFCs), for applications in both military and commercial markets. A requirement for high efficiency is that the fuel cell be operated at as high a cell voltage as possible while still producing a practical current density. This implies that the open circuit voltage (OCV) must be near theoretical in order to achieve high operating potential. A commonly stated problem with the planar SOFC design is the difficulty in sealing adjoining cells to the bipolar interconnects. However, experimental evidence indicates that because the OCV is strongly affected by a non-uniform or {open_quotes}mixed{close_quotes} potential due to cell edge leaks, estimates of leakage from OCV are much greater than actual leakage. A second phenomenon that affects the OCV of a SOFC stack is the mixed conduction exhibited by the interconnect material. The effects of these mechanisms on SOFC operational performance and efficiency are discussed.