| 摘要: | 鈣鈦礦結構氧化物具有相當多的性質，尤其是其電子與離子傳導特性，故廣泛應用於固態氧化物燃料電池中。如：質子傳導固態氧化物燃料電池中之陽極與電解質材料、及氧離子傳導固態氧化物燃料電池中之陰極材料，甚至當作保護層材料披覆於金屬連接板表面上。本論文則主要討論La0.67Sr0.33MnO3(LSMO)鈣鈦礦氧化物當作保護層材料批覆於金屬連接板表面上、與SrCeO3質子傳導電解質材料。
在La0.67Sr0.33MnO3保護層研究方面，首先分別選擇Crofer22 APU, Crofer H, ss441 及兩個不同成分之ZMG232 之Fe-Cr合金。主要探討這五種材料於800℃高溫環境下之高溫抗氧化性與鉻揮性等。利用SEM/EDS與XRD來觀察及分析材料微結構變化與氧化層成分分析。高溫電阻則利用四點探針法進行量測。結果顯示，Crofer22 APU材料相較於其他四種材料，在長時間高溫環境下呈現出較薄氧化層厚度、較低的高溫電阻與較少的鉻揮發。
為了進一步提升連接板高溫抗氧化性，利用脈衝直流磁控濺射法、氣膠沉積法和網版印刷法、將La0.67Sr0.33MnO3（LSMO）塗覆於連接板表面上當作保護層。並於高溫氧化的環境下分析其高溫電阻變化及鉻揮發。實驗結果顯示，脈衝直流磁控濺射製程可製備出高品質與高緻密性保護層，能有效降低連接板之高溫電阻及減緩鉻向外揮發。
在質子傳導電解質材料方面，選擇SrCeO3當作基本材料，將鉀與釔分別摻雜於SrCeO3材料A-與B-site中 ，利用固態反應法製備出Sr1-xKxCe0.95Y0.05O3, (x=0, 0.025, 0.05)材料。並探討鉀的摻雜對於SrCe0.95Y0.05O3材料於氫氣與二氧化碳氣氛下、對於導電率及化學穩定性的影響。以X光粉末繞射儀(XRD)分析材料相與結構的變化，場發掃描式電子顯微鏡(FE-SEM)觀察材料表面形貌；利用兩點式電阻量測法分別在550, 600, 700, 800 及900℃濕氫氣(RH 30%)氣氛下進行電導率測試；化學穩定性則在600℃、1 atm二氧化碳氣氛下，分別進行2、4、8與16小時穩定性測試。結果顯示，鉀跟釔的摻雜能增加SrCeO3材料的導電率。Sr0.95K0.05Ce0.95Y0.05O3於900℃濕氫氣氣氛導電率可達到0.0081 S/cm2。在化學穩定性方面，鉀跟釔的摻雜無助於SrCeO3材料之化學穩定性，此現象也限制Sr1-xKxCe0.95Y0.05O3材料在固態氧化物燃料電池上的應用。
;Perovskite oxides exhibit wide range of electrical and ionic conductivities. They are extensively used as main materials in various components of the solid oxide fuel cells (SOFCs). For example, proton-conducting SOFCs (P-SOFCs) often choose perovskites as anode and electrolyte. On the other hand, in oxygen-conducting SOFCs (O-SOFCs), perovskites are used as cathode and protective layer for interconnects. This thesis presents studies about perovskites for the protection of La0.67Sr0.33MnO3 interconnects in O-SOFCs, and SrCeO3-based proton-conducting electrolyte in P-SOFCs.
For the part of La0.67Sr0.33MnO3 protective layer, five Fe-Cr interconnects, Crofer22 APU, Crofer H, ss441 and two different ZMG232 were selected for high temperature and long term oxidation tests. Our major focus is on these naked materials’ resistance to oxidation and Cr evaporation. The microstructures, morphologies and compositions of samples after oxidation are analyzed by SEM, XRD, EDS on surfaces and cross-sections. Electrical resistance of samples during oxidation is measured by four-point probe to obtain their variations over time. Experimental results revealed that Crofer22 APU has a better performance than others after long-hour oxidation with thinner oxidized layer, lower electrical resistance and less Cr evaporation.
After the oxidation study of naked Fe-Cr interconnects, La0.67Sr0.33MnO3 was coated on interconnects by pulsed-DC magnetron sputtering, aerosol deposition and screen printing respectively. The effects of coating processes and oxidation tests on these coated interconnects were carried out and systematically investigated. The experimental results indicate that the pulsed-DC magnetron sputtering yields much denser La0.67Sr0.33MnO3 protective layer on the interconnects, which leads to lower electrical resistance and Cr evaporation.
For the part of SrCeO3-based electrolyte. SrCeO3 was selected as base-material for their well-known proton-conducting capacity. We studied two different doping elements, i.e. the potassium and yttrium for their influence on the overall electrical/proton conductivities and chemical stability under various atmospheres (H2 and CO2). The potassium is a substitution for Sr (A-site substitute) while the yttrium is for Ce (B-site substitute). The doping content is well controlled and by solid state reaction to give the final products as Sr1-xKxCe0.95Y0.05O3 (x=0, 0.025, 0.05). Results show that conductivity of these new perovskites in moisture H2 atmosphere (RH 30%) can be enhanced with the increasing potassium concentration. The maximum conductivity of Sr0.95K0.05Ce0.95Y0.05O3 was found to attain 0.0081 Scm-1 at 900℃ in moisture H2 atmosphere (RH 30%). Overall speaking, the potassium- and yttrium- doped SrCeO3 possess higher conductivity but retain relatively not good CO2 resistance. Both issues are vital in solid oxide fuel cell applications. |
