The two most common designs of SOFCs are the tubular and the planar (Singhal, 2002)。 The tubular cell of Siemens Westinghouse design is shown in Figure 1。 The cell components might be deposited in the form of thin layers on a doped lanthanum manganite cathode tube (Singhal, 2000)。 The cathode tube is fabricated by extrusion and sintering, while YSZ electrolyte is deposited in the form of about 40 mm thick dense layer by electrochemical vapour deposition。 Finally, the Ni/YSZ anode is deposited either by nickel slurry application followed by electrochemical vapour deposition of YSZ or by sintering of a Ni/YSZ slurry。 The doped lanthanum chromite interconnection strip along the length of the cell is deposited by plasma spraying。 The image in Figure 1(b) shows six HPD5 and nine Delta9 cells fabricated by Siemens Westinghouse。 Those cells, due to increased surface area in comparison to tubular cells, exhibit improved performance and therefore are their successors。
Figure 1 Tubular design of SOFC: (a) schematic diagram; (b) real stack
Source: Courtesy of Siemens Westinghouse
Their electrical efficiency is of about 200 and 600 mW/cm3 (of about 0。3 W/cm2), respectively。
In the planar design the cells are prepared in the form of thin and flat plates as shown in Figure 2。 The interconnection is in a form of plate corrugated on both sides, which forms gas flow channels and serves as a bipolar gas separator contacting the anode and the cathode of neighbouring cells。 The cells are usually fabricated by low-cost conventional ceramic processing techniques such as tape casting, slurry sintering, screen printing and plasma spraying。 The power efficiency can reach 2 W/cm2 in case of the anode supported cells with YSZ electrolyte of about 10 mm thick。 Specific power density of planar design can be one order of magnitude higher than in tubular design。 Even though the tubular design has a huge advantage over planar, because the high-temperature seals are not necessary for tubular cells operation。 The high- temperature seals, which are required for planar design, are one of technological challenges and still need to be improved。 The images of stacks shown in Figures 1(b) and 2(b) are designed rather for stationary or mobile application, which require more than 5 kW of power, so it is hard to call them mSOFC。 Currently in Japan is being developed a SOFC system, which is called micro tubular SOFC (Funahashi et al。, 2007; Suzuki et al。, 2006, 2007)。 This system is based on ceramic technologies, which are used to prepare tiny elements。 In Figure 3 are presented images of such a system。 The single cells consist of 70 wt% NiO-Gd doped ceria (GDC) as an anode (support tube), GDC as an electrolyte and 70 wt% (La, Sr)
Figure 2 Planar design of SOFC: (a) schematic diagram; (b) real stack
Figure 3 (a) SEM image of cross section of single cell; (b) real stack
Source: Courtesy of AIST Nagoya
(Fe, Co)O3-GDC as a cathode。 The NiO-GDC tubes (1 mm in diameter) are extruded from a plastic mass using a die forming。 After drying, the tubes are cut to length and then dip-coated in a GDC slurry to form an electrolyte。 The coatings are left to dry in air, then sintered at 1,4508C。 Next, the tubes are dip-coated in cathode slurry。 After dip-coating, to complete a cell, the tubes are dried in air and sintered at 1,0008C。 Simultaneously matrices are prepared by extruding the clay from a metal mold using a screw cylinder type extruder。 The extruded matrices are cut to 3 cm long, dried and sintered in air。
Following, matrixes and tubes are assembled into cube
shaped micro tubular SOFC stack according to procedure shown in Figure 4。 The bonding paste, which is made of LSCF powder, is screen-printed on the surface of the cathode matrices。 The tubular cells are placed into the matrix before the paste is dried。 After the cube is assembled by sandwiching the cathode matrices and the tubular cells, the cube is sintered at 1,0008C for 1 h in air。 The stack (size of 3 £ 3 £ 3 cm) prepared in this way shows excellent performance of 2 W/cm3 (about 1 W/cm2)。 微型固体氧化物燃料电池英文文献和中文翻译(2):http://www.youerw.com/fanyi/lunwen_101140.html