Orta sıcaklıklı katı oksit yakıt pilleri için LSC-113/LSC-214 katot malzemelerinin geliştirilmesi.

Solid oxide fuel cells are environmentally friendly, efficient and fuel versatile energy conversion devices which suffer from high operating temperatures. For lowering the operating temperatures of solid oxide fuel cells (SOFC), LSC-113/LSC-214 composite cathodes have recently attracted much attention due to their enhanced kinetics. However, the full potential of this novel system is still unknown. In this study, a combinatorial approach was used to develop cathode materials which would reduce operating temperatures of SOFCs to the range 500 - 600 ⁰C. The kinetics of cathodic processes were investigated for LSC-113/LSC-214 composite cathode films deposited with magnetron sputtering and screened with measurement of EIS responses on symmetric cells. The study is made up of three parts. Part I is related to the fabrication of sputtering targets. Part II comprises the main study which was on combinatorial screening of LSC-113/LSC-214 co-sputtered cathodes, and Part III is related to the stability of composite LSC cathodes for prolonged use; In the first part of this study, a novel approach is illustrated to fabricate sputtering targets for thin film production. In this approach, deformable dies made up of poly-tetrafluoroethylene (Teflon) were used instead of conventional rigid dies. It was shown that this method is suitable for products of low volume productions. With the use of teflon rings LSC-113 and LSC-214 sputtering targets were succefully fabricated and used for the deposition of thin film cathodes. In the second part, a combinatorial approach was used to obtain the optimum composition in LSC-113/LSC-214 composite system. A thin film composite cathode library was obtained by co-sputtering of LSC-113 and LSC-214 onto suitably positioned substrates each with controlled compositions. The cathode library was screened with an electrochemical impedance spectroscopy and showed that co-sputtered LSC-113/LSC-214 composite cathodes have low area specific resistance values (ASR) as compared to those reported in the literature. Practically useful ASR value of 0.15 Ω.cm2 was obtainable at many of the compositions in LSC-113/LSC-214 below 700 ⁰C. The best compositional range is 0.40M.S. - Master of Scienc

FEN BİLİMLERİ ENSTİTÜSÜ/LİSANSÜSTÜ TEZ PROJESİ

METAL HİDRÜRLE EŞLEŞTİRİLMİŞ KATI OKSİT HÜCRELER İÇİN ARAYÜZEY KONTROLLÜ MALZEMELERİN GELİŞTİRİLMES

İnce Film-Katı Oksit Yakıt Pillerinde Performans Optimizasyonu

Katı oksit yakıt pilleri sahip oldukları yüksek enerji verimliliği, alternatifli yakıt seçenekleri ve çevre dostu olmak gibi üstün özelliklerinden dolayı yeni nesil enerji cihazlarının geliştirilmesi alanında son derece dikkat çeken enerji dönüşüm düzenekleridir. Oksit malzemelerde difüzyon mekanizmasını aktive etmek için gerekli olan yüksek sıcaklıklar, katı oksit yakıt pillerinin hem üretim hem de kullanım aşamalarında düşük güvenlik, yüksek maliyet ve kısa çalışma ömrü gibi çeşitli zorlukları beraberinde getirmektedir. Bu nedenle çalışma sıcaklıklarının 1000⁰C gibi yüksek sıcaklıklardan 600⁰C gibi orta sıcaklık seviyelerine çekilmesi gerekmektedir. Bu amaç doğrultusunda ince film teknikleriyle üretilen düzenekler önem kazanmaktadır. Bu proje, ileri üretim teknikleriyle hazırlanan ince film-katı oksit yakıt pillerinin performanslarının ölçülmesi, bu doğrultuda elektrot ve elektrolit malzemelerinin kalınlıkları, çalışma sıcaklıkları ve yakıt verimliliği gibi parametrelerin optimizasyonlarının yapılmasını kapsamaktadır. Bu sayede orta sıcaklık seviyelerinde yüksek verimlilikle çalışabilen uzun ömürlü katı oksit yakıt pillerinin üretilebilmesi hedeflenmektedir. Başarılı olunması durumunda enerji verimliliğinin son derece yüksek olduğu yeni bir düzenek elde edilmiş olacaktır

SYNTHESIS OF DUAL PHASE CATHODE FOR IT SOFCs VIA THERMAL PLASMA

The combinatorial approach is particularly suitable for identification of suitable cathode materials. This involves a simultaneous deposition of thin film cathodes each with a different composition in a single experiment. The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). A main goal in SOFC research is the development of cathodes with a sufficiently low electrochemical resistance (- 0.15 Q.cm2) at operating temperatures significantly below 800°C. Focus has been shifted to particularly mixed conducting perovskites of the La I -xSncCo03-8 (LSC), Lal–xSniMnO3AZ (LSM), LaxSrl–xCoyFel–y03-8 (LSCF) family [1]. Since, Cnunl in et al.[2] and Sase et al. [3] exhibit improved electrochemical performance with hetero-structures [4]. Oxygen surface exchange was found to be enhanced at the heterointerface of LSC214/LSC113 [3]. It was recently shown that the sputter deposited (La0.8Sr0.2) Co03 (LSC-113) - (La0.5Sr0.5)2Co04 (LSC-214) dual phase cathode yield the best performance where the mixture had an amorphous-like structure [5]. In this study a composite cathodes LSC113- LSC214 and LSF-LSM were synthesized via thermal plasma using a large flow rate of quenching gas yielding non-equilibrium cathode powder. The purpose is to see if similar performance improvement could be obtained with plasma synthesized composite powders. The powders were screen printed onto suitable electrolytes and were characterized based on EIS responses using a symmetric cell under air. The typical EIS response at 500°C is given in Fig

Synthesis of Dual Oxide Cathode for IT-SOFCs via Th ermal Plasma

The composition and microstructure of cathode materials has a large impact on the performance of solid oxide fuel cells (SOFCs). It was recently shown that the sputter deposited (La0.8Sr0.2) CoO3 (LSC-113) - (La0.5Sr0.5)2CoO4 (LSC-214) dual phase cathode yield the best performance where the mixture had an amorphous-like structure. In this study a composite cathode of LSC-113: LSC-214 was synthesized via thermal plasma using a large flow rate of quenching gas yielding non-equilibrium cathode powder. The purpose is to see if similar performance improvement could be obtained with plasma synthesized powder. Powder obtained were then screen printed onto the gadolinium doped ceria (Gd0.1Ce0.9O1.95) electrolytes and were characterized based on EIS responses using a symmetric cell under air

Preparation of La0.8Sr0.2CoO3-δ / (La0.5Sr0.5)2CoO4 Sputtering Targets Using Deformable Compaction Die

Fabrication of sputtering targets deviates from the customary practices in ceramic processing as their production volumes are often quite low. The use of hot-press, in this context, greatly facilities the fabrication of sputter targets since both the density and the dimensions of the target are controlled during the pressing. In the absence of hot press, however, the fabrication requires extensive preliminary work, but difficult to justify due to limited volume production. In this study, in place of customary rigid die, we propose the use of a deformable die which greatly simplifies the fabrication procedure. In this approach, polytetrafluoroethylene (PTFE) rings are used as compaction die filled with powders, tapped to uniform density. The die is then deformed between parallel platens whereby compacting the powders. The method relies on the fact that the pressing leads to almost no change in the internal diameter of the ring. This approach was illustrated with the fabrication of 2 in. La0.8Sr0.2CoO3-δ (LSC-113) target where the deformable die was dimensioned by preliminary experiments on PTFE rings of small diameter. Sputter targets of sintered density greater than 0.95 and dimensions within the tolerances of the sputter gun were successfully fabricated. It is proposed that the approach may also be applicable to flat products of irregular shape, as high friction in tapped particulate media makes the lateral flow difficult, confining the compaction mainly to axial direction