A new type of solid oxide fuel cells (SOFC) has been developed, realizing reduction of fuel cell operating temperature while maintaining high efficiency, especially for the use of fuel cells in portable devices and distributed energy production systems. These fuel cells are comprised of extremely thin layers fabricated by thin-film deposition processes.  This thin-film SOFC design incorporates an electrolyte thin-film layer of thickness less than 1mm on a foil nickel substrate followed by lithographic patterning of the foil substrate to form a porous anode, and finally followed by the deposition of a thin-film oxide cathode to complete the thin-film SOFC structure. These processes are similar, but less complex than processes used in the microelectronics industry, and promise extremely cost effective production possibilities.

The thin-film fuel cell is comprised of three principal layers: anode, electrolyte and cathode.  These thin film layers are deposited by commercially viable metallorganic chemical vapor deposition or pulsed laser deposition. The fuel cell thin film electrolyte layer, currently yttria-stabilized zirconia (YSZ), is deposited on a nickel foil, which is used as the substrate for the cell fabrication process and also as the anode of the fuel cell.  Since the nickel foil substrate is required to be porous to form the anode, the Ni side of substrate foil (after YSZ electrolyte deposition) is subjected to photolithographic patterning, and chemical or electro-chemical etching to develop pores in the nickel substrate. The pore structure can be varied to obtain improved fuel cell performance and is somewhat dependent on Ni substrate foil thickness.

The crux of this thin film solid oxide fuel cell design is the ultra-thin nature of the solid oxide electrolyte.  This results in a major reduction in cell operating temperatures. As a result, the thin-film fuel cells can operate over a temperature range of from 450 to 550°C. The performance of a typical YSZ-based thin film fuel cell as a function off temperature is shown (at right). The cell open circuit voltage is over 0.8V and is being increased with a new sealing design.   The maximum cell output power increases with an increase in temperature varying from 30mW/cm2 at 480°C to a maximum power output of ~110mW/cm2 at 570°C. This maximum power output is lower than that for bulk SOFC’s operating at 900°C, however, it is much higher than bulk SOFC’s or other ‘thin’ film SOFC’s operating at 550°C.