Perovskite Oxide for Solid Oxide Fuel Cells
The continuing development of fuel cells offers promising technologies for the conversion of chemical energy from hydrocarbon fuels into electricity without forming air pollutants. Perovskite Oxides for Solid Oxide Fuel Cells provides insight into the mat
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Overview of Intermediate-Temperature Solid Oxide Fuel Cells Harumi Yokokawa
2.1 Introduction The first breakthrough in solid oxide fuel cell (SOFC) technology was achieved by Westinghouse Power Corporation (WHPC; currently Siemens Power Generation Corporation) [1] in the late 1980s in their efforts in establishing tubular SOFCs with the following technologically important points: 1. Optimizing the materials [yttrium-stabilized zirconia (YSZ) for the electrolyte, lanthanum strontium manganite for the cathode, nickel for the anode, and lanthanum magnesium chromite for the interconnect]. 2. Adopting an excellent processing technology of electrochemical vapor deposition (EVD) [2] that has extraordinary advantages in fabricating dense films on porous materials or in anchoring nickel on YSZ. 3. Adopting a sealless tubular stack design to avoid usage of sealant materials. 4. Aiming for stationary applications. This breakthrough leveraged up the development of the SOFC stacks/ systems from the R&D stage to a more realistic stage with specifically targeted market sectors. The long operation life was successfully demonstrated, and also the high conversion efficiency from natural gas to electricity was demonstrated as 47% Lower Heating Value (LHV) for stationary 100-kW SOFC systems and as 52% for combined SOFC-gas turbine systems. Immediately after the first breakthrough with sealless tubular cells, detailed analyses were made by Ackerman at the Argonne National Laboratory (ANL) to identify the merits and demerits of the sealless tubular cells [3]. The main disadvantages were pointed out as follows:
H. Yokokawa (*) Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology, Higashi 1-1-1, AIST Central No.5, Tsukuba, Ibaraki 305-8565, Japan e-mail: [email protected]
T. Ishihara (ed.), Perovskite Oxide for Solid Oxide Fuel Cells, Fuel Cells and Hydrogen Energy, DOI 10.1007/978-0-387-77708-5_2, Ó Springer ScienceþBusiness Media, LLC 2009
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1. High fabrication costs because the EVD process utilizes metal chloride vapors in vacuum. 2. Low volumetric power densities because the electrical paths lie transversely along the cathode layer in tubular cells. Since then, various attempts [4–6] have been made to investigate the following main points: 1. Planar cells to improve the power density. 2. Tubular cells to lower the fabrication cost or to increase the power density. The next new wave in developing solid oxide fuel cells arose around the mid-1990s. One of the biggest achievements in this period was the discovery of a new oxide ion conductor, namely, lanthanum strontium gallium magnesium oxides (LSGM), by Ishihara in 1994 [7, 8]. Another important impact on SOFC technology was the proposal of using SOFCs as auxiliary power units for automotive applications by BMW and Delphi [9]. A similar proposal was made by ANL for monolithic SOFCs in the late 1980s [10] in their efforts to overcome the demerits of sealless tubular cells. Even so, the proposal by BMW/ Delphi w
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