6deposition of YSZ on Ni/YSZ composite film by rf sputtering technique;
7deposition of Ag and YSZ on YSZ film by dc and rf sputtering technique, respectively;
8deposition of Ag on Ag/YSZ composite film by dc sputtering technique; and
9removal of silicon nitrate from backside of structure by reactive ion etching。
Prepared in this way mSOFC-MEMS provides 0。15 W at 3168C (Morse and Jankowski, 1999)。 The film can be deposited by other techniques, e。g。 pulse laser deposition (Rupp and Gauckler, 2006), but the sputtering methods are the most popular (La O et al。, 2004; Hertz and Tuller, 2004; Bieberle-Hutter and Tuller, 2006)。
Currently the ETH, Zurich is developing the mSOFC system called ONETBAT。 It is fabricated on Foturanw which is a glass ceramic 300 mm thick substrate, by spray pyrolysis, pulse laser deposition or sputtering (Bieberle-Hu¨ tter et al。, 2005, 2008)。 To prepare the mSOFC, first the platinum current collector-anode (,50 nm thick) is deposited and then on top subsequently the ,550 nm thick YSZ electrolyte and
,200 nm thick LSCF perovskite cathode。 Next, the structure is annealed at 6008C to crystallize the ceramic layers and then
Figure 7 Schematic view of mSOFC prepared by MEMS technology
Cathode Electrolyte Anode
O2 (0。21 atm) e–
Silicon support
Source: Srikar et al。 (2004) reproduced with permission of Elsevier
the selected parts of the Foturanw substrate are UV-exposed and back etched to release the ceramic membrane。 The mSOFC at 5508C provided the open circuit voltage of
1。06 V and the power of 150 mW/cm2。
It is important to note that the ceramics films are deposited at low temperature and therefore most likely they are going to have nanocrystalline structure。 Therefore, one might expect that the grain boundary conductivity might be a significant portion of the electrolyte total conductivity, which will influence the performance of the mSOFC。 As an example, the temperature dependence of nanocrystalline conductivity of samarium doped ceria electrolyte is shown in Figure 8。
3。Single chamber solid oxide fuel cells
The working mechanism of SC-SOFC operation is based on the difference in electrocatalytic activity of the electrodes to air and hydrocarbon。 If anode is catalytically active to hydrocarbon reforming, then a following chemical reaction is expected to occur (1):
O2 þ 4e2 ! 2O22 ð2Þ
H2 þ O22 ! H2O þ 2e2 ð3Þ
CO þ O22 ! CO2 þ 2e2 ð4Þ
Reaction (1) is exothermic and causes increase of the fuel cell temperature。 This is advantageous because the higher temperature lowers resistances of electrolyte and electrodes。
The major advantage of SC-SOFCs is a possibility of direct use of hydrocarbon without loss of fuel cell performance。 While in case of the SOFC direct use of hydrocarbon fuel usually leads to carbon deposition on anode side and as a result the fuel cell performance decrease。 Another advantage is related to the possibility of application of porous electrolyte (Suzuki et al。, 2005), because mechanism of operation is based on difference of catalytic activities of electrodes。 This significantly simplifies technological requirements and cost effective technologies can be used for fuel cell fabrication,
e。g。 screen printing (Suzuki et al。, 2005)。 A major drawback of the SC-SOFCs is lower fuel utilization than conventional 微型固体氧化物燃料电池英文文献和中文翻译(4):http://www.youerw.com/fanyi/lunwen_101140.html