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Independent Professional: Experienced educator and management consultant for engineering educational institutions, researcher, trainer, technical consultant on sustainable technologies, related to cement manufacturing and characterisation, using industrial and agricultural wastes in cement and concrete, durability of concrete and fuel cell power.

Friday, December 18, 2009

IT-SOFC

Due to their high efficiency, solid oxide fuel cells (SOFC) not only conserve valuable natural resources but also assist in reducing pollution and greenhouse gas (GHG) emissions. However, long-term degradation problems associated with the high-temperature operation and relatively high manufacturing costs remain the main challenges for the commercialization of this technology. Lowering the operating temperature to an intermediate temperature (IT) range (400–700 °C) not only improves reliability but also lowers the cost, time and energy. This will extend its application domain to residential power and portable devices. However, with the current state-of-the-art SOFC materials, it is not possible to obtain sufficient power in the IT range. This is because of high ohmic losses and electrode polarization, which have a detrimental effect on performance and efficiency. Thus, there is a need to develop materials that show improved properties in the IT range.

High ionic conductivity solid oxide electrolytes are critical for the development of SOFCs that can successfully generate reasonable power at IT range. In recent years, doped ceria electrolytes have emerged as a potential candidate due to their higher ionic conductivity than that of the conventional yttria stabilized zirconia (YSZ) at intermediate temperatures. Among doped ceria materials, Gd0.10Ce0.90O2−δ (GDC) is widely accepted to exhibit the high ionic conductivity in the IT range. However, recent research shows that co-doping based on Sm3+ and Nd3+ leads to further enhancement in the ionic conductivity in ceria systems [3] S. Omar, E.D. Wachsman and J.C. Nino, Appl. Phys. Lett. 91 (2007), p. 144106. Full Text via CrossRef | View Record in Scopus | Cited By in Scopus (8)[See Ref.]. Optimization of dopant concentration in the Smx/2Ndx/2Ce1−xO2−δ system resulted in the development of Sm0.075Nd0.075Ce0.85O2−δ (SNDC), which exhibits 30% higher grain ionic conductivity than that of GDC at 550 °C in air.

The current–voltage performance of the cell was measured at intermediate temperatures with 90 cm3 min−1 of air and wet hydrogen flowing on cathode and anode sides, respectively. At 650 °C, the maximum power density of the cell reached an exceptionally high value of 1.43 W cm−2, with an area specific resistance of 0.105 Ω cm2. Impedance measurements show that the power density decrease with decrease in temperature is mainly due to the increase in electrode resistance. The results confirm that Sm0.075Nd0.075Ce0.85O2−δ is a promising alternative electrolyte for intermediate temperature solid oxide fuel cells.

Ref.: Jin Soo Ahn, Shobit Omar, Heesung Yoon, Juan C. Nino and Eric D. Wachsman, “Performance of anode-supported solid oxide fuel cell using novel ceria electrolyte”, Journal of Power Sources, Volume 195, Issue 8, 15 April 2010, Pages 2131-2135