| It is agreed that solid oxide fuel cells (SOFC) hold the greatest potential of any alternative generators onboard for their efficient, clean, calm and dependable nature. Upon the recent developments of SOFC technologies, the working temperature for it has been significantly depressed into medium-low regime (600-800℃), which could make it possible of metallic interconnecter, especially stainless steel. However, both the long-term oxidation resistance and surface conductivity of stainless steel, and performance and compatibility of cathode material under high temperature will contribute to the reliability and output characteristics of SOFC.Electric pulse deposition method was used in the research to pre-oxidize stainless steel and create two different modification layers:MnCo2O4 and NiCo2O4 on the surface of SUS430. The oxidation kinetics and surface conductivity of this treated SUS430 was examined. Three different electrolytes were made, and the thermo-expansion property and electric conductivity of these three cathodes were tested. Composite cathodes were made with doping electrolyte to cathode materials. The thermo-expansion compatibility among composite cathode, electrolyte and modified interconnecter was also investigated.The MnCo2O4 and NiCo2O4 spinel powder were made using sol-gel dip-coating method in this study. The high temperature conductivities at 800℃ of the two kinds of spinel are 17.6 S·cm-1 (MnCo2O4) and 24.3 S·cm-1 (NiCo2O4), the thermo-expansion coefficients (TEC) of them are 11.5×10-6K-1 (MnCo2O4) and 11.8×10-6K-1 (NiCo2O4). The results indicate that their TECs are very close to that of SUS430 bulk (11.0×10-6 K-1). It can be concluded that all the tow kinds of spinel are very good candidates as modification layer materials on metallic interconnect.The pulsed electricdeposition method was also used to pre-oxidize stainless steel and create two different modification layers on the surface of SUS430:MnCo2O4 and 4. The Co-Ni spinel was first used as the modified surface layer of SOFC interconnecter. The characterization results show that the modification layers are uniform and compact, and in good connection with SUS430 bulk.These two modification layers can significantly reduce oxidation rate of SUS430 in simulated SOFC working environment. The MnCo2O4 modification layer shows a better performance, which decreased the oxidation rate of SUS430 from 2.702×10-4 mg2·cm-4·s-1 to 0.717×10-4 mg2·cm-4·s-1, so did the NiCo2O4 modification layer to 1.189×10-4 mg2·cm-4·s-1. In addition, the two kinds of spinel can increase the oxidation activation energy of SUS430 from 193.07 KJ·mol-1 to 275.94 KJ·mol-1 (MnCo2O4) to 250.13 KJ·mol-1 (NiCo2O4). The ASR of SUS430 with MnCo2O4 modification layer is lowered from 410 mΩ·cm2 to 206 mΩ·cm2 after 500 hours, so did that of NiCo2O4 is about 99 mΩ·cm2. It can be concluded that both the two kinds of spinel significantly promote the oxidation resistance at high temperature and surface conductivity of SUS430.Three different cathode materials were made in this study, which are La0.7Sr0.3MnO3-δ (LSM), La0.6Sr0.4Fe0.8Co0.2O3-δ (LSFC) and La0.7Sr0.3Co0.95Cu0.05O3-δ (LSCC). The TEC and electrochemical measurements show that LSCC has much better electrochemical property than the other two. The TEC of LSM has best match with SUS430. With doping SDC into LSCC, a new composite cathode material was made, which can decrease the TEC in LSCC, and also improve the electrochemical property. The high power output was got in a single cell test, which showed a short circuit current density of 0.352 A/cm2 and maximum output of 75 mW/cm2 at 800℃. |
PDF Full Text Request