Polygeneration systems attract attention recently because of their high efficiency and low emission compare to the conventional power generation technology. Three different polygeneration systems based on low temperature solid oxide fuel cell, atmospheric solid oxide fuel cell/ micro gas turbine, and pressurized solid oxide fuel cell/ micro gas turbine are mathematically modeled in this study using MATLAB (version 7.12.0.635). These systems are designed to provide space heating, cooling and hot domestic water simultaneously. This report provides the design aspects of such systems. Furthermore, the effects of some important operating properties on the polygeneration systems performance are investigated.

Ceramics oxides with mixed ionic and electronic conductivity have received a lot of attention due to their wide range of applications in solid oxide fuel cells, interconnects, gas sensors, and ion transport membranes. However, owing to harsh operating conditions, the choice of proper materials and engineering their properties are still challenging. Perovskite and fluorite structures are two promising structures for ceramic membrane applications. The objective of this research is to explore the stability of lanthanum chromite-based perovskite ((La,Sr)(Cr,Fe)O3-δ) as single phases and dual-phase composites with fluorite phases under fabrication and operating conditions of Oxygen Transport Membranes (OTM). The current research has been categorized into two sections: structural and chemical stability of perovskite phases and dual-phase perovskite/fluorite composites. Also, investigation on both categories has been conducted with two separate approaches: experimental examinations and computational Thermodynamic. In the computational part, independent methods have been considered for the single-phase perovskite and dual-phase perovskite/fluorite composites. In the experimental section, the bulk chemical stability of the dual-phase samples has been examined under controlled oxygen partial pressure p(O2) atmospheres at 1400ᵒC for 10 hours with slow and fast cooling rates. Besides, the phase stability of the perovskite structures as a single-phase has been also examined under OTM fabrication conditions. The results present new phenomena in the chemical stabilities of the materials. They include formations of liquid phases, Sr-segregation, and perovskite phase separations. The correlations between compositions/ temperature/ p(O2) and secondary phases have been investigated to improve the chemical stability and extend the lifetime of the materials. The findings in this thesis enhance the knowledge about the chemical stabilities of OTMs and help to develop more reliable materials for ceramic-based OTMs.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19703号 / 工博第4158号 / 新制||工||1641(附属図書館) / 32739 / 京都大学大学院工学研究科航空宇宙工学専攻 / (主査)教授 吉田 英生, 准教授 岩井 裕, 教授 鈴木 基史, 教授 江口 浩一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19730号 / 工博第4185号 / 新制||工||1645(附属図書館) / 32766 / 京都大学大学院工学研究科物質エネルギー化学専攻 / (主査)教授 江口 浩一, 教授 安部 武志, 教授 陰山 洋 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21424号 / 工博第4534号 / 京都大学大学院工学研究科航空宇宙工学専攻 / (主査)教授 吉田 英生, 教授 黒瀬 良一, 准教授 岩井 裕, 教授 江口 浩一 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Atomistic modelling has widely been applied for studying structures and properties of materials. There are various methods to perform atomistic modelling. This master thesis presents a combined density functional theory (DFT) and cluster expansion (CE) study of Gd2O3 and Gd2O3-CeO2 interface (GCI) relevant for solid oxide fuel cells (SOFCs).    The energy differences (ΔE) of Va-O exchanges in C-type Gd2O3 and at GCI are calculated using both DFT and CE methods. We also calculated the migration energy (Emig) of Va jumps in Gd2O3 and at GCI by DFT. The comparison between the CE and DFT results demonstrates that the CE method provides a relatively accurate estimation of ΔE while it requires less computational resources. Furthermore, the CE method is used to study the Va migration in the vicinity of the Gd2O3-CeO2 interface. The potential energy landscapes of different types of paths are studied. / Atomistisk modellering har i stor utsträckning använts för att studera strukturer och  egenskaper  hos  material.  Det  finns  många  olika  metoder  för  att  utföra atomistisk   modellering.   Detta   masterprojekt   presenterar   en   kombinerad density functional theory (DFT) och   cluster expansion (CE) studie av Gd2O3- och Gd2O3-CeO2 gränssnittet (GCI), relevant för fastoxidbränsleceller (SOFC). Energiskillnaderna (ΔE) för Va-O-utbytet i C-typ Gd2O3 och vid GCI beräknas med   användning   av   både   DFT-   och   CE-metoder.   Vi   beräknade   också migrationsenergin   (Emig)   av   Va-hopp   i   Gd2O3   och   vid   GCI   med   DFT. Jämförelsen  mellan  CE  och  DFT-resultaten  visar  att  CE-metoden  ger  en relativt    noggrann    uppskattning    av ΔE    samt    att    den    kräver    mindre beräkningsresurser.   Vidare   används   CE-metoden   för   att   studera   Va- migrering  i   närheten   av   Gd2O3-CeO2-gränssnittet.   Det   potentiella   energilandskapet  för olika vägar studeras.

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No description available.

Solid Oxide Fuel Cells (SOFC) are attractive candidates in the search for cleaner and energy efficient production due to their numerous advantages such as fuel flexibility, modularity and exceptional efficiencies when combined heat and power is harnessed. A key element in its design are the interconnects which are mainly manufactured from custom ferritic stainless steels to carry the electricity between two adjacent cells. However, the high operation temperatures increase the chromia scale thickness in those steels, which reduces their conductivity. At the same time, chromium (VI) volatilization due to the wet atmosphere poisons the electrodes and reduces the cell life. Therefore, the narrow of the selection of suitable materials and high production costs have hindered their commercialization. Recent advances in lower temperature SOFC operation have opened a window for new interconnect materials and innovative processes. A Ce/Co nanocoating can be applied in the readily available AISI 441 ferritic steel to form a protective spinel oxide layer that reduces the effect of both degradations in the interconnects. The coating is applied in a continuous roll-to-roll process and then the interconnect shape is pressed in the material, manufactured as Sanergy HT 441 by Sandvik. However, mechanical stresses cause microcracks that expose the substrate material, which can impact the oxidation behaviour negatively. Fortunately, pre-treatments can achieve the spinel to diffuse over short distances and combine with elements in the substrate, homogenizing the protective effect. This phenomenon known as self-healing has not been studied with sufficient depth for the Sanergy HT 441. Thus, different series of temperature and short pre-treatments times were tested, and self-healing properties were observed by means of SEM surface characterization and chemical analysis. The results indicate that self-healing can be obtained within short times using isothermal pre-treatments at temperatures over 750 °C. / Solid Oxide Fuel Cells (SOFC) är attraktiva kandidater i jakten på renare och energieffektiv produktion på grund av deras många fördelar som bränsleflexibilitet, modularitet och exceptionella effektivitet när kombinerad värme och kraft utnyttjas. Ett viktigt element i dess utformning är sammankopplingar som huvudsakligen tillverkas av anpassade ferritiska rostfria stål för att transportera elektricitet mellan två angränsande celler. De höga driftstemperaturerna ökar emellertid tjockleken på kromskalan i dessa stål, vilket minskar deras konduktivitet. Samtidigt förorenar krom (VI) på grund av den våta atmosfären elektroderna och reducerar celllivslängden. Därför har det smala urvalet av lämpliga material och höga produktionskostnader hindrat deras kommersialisering. De senaste framstegen inom SOFC-drift med lägre temperatur har öppnat ett fönster för nya sammankopplingsmaterial och innovativa processer. En Ce / Co-nanocoating kan appliceras i det lättillgängliga AISI 441 ferritstålet för att bilda ett skyddande spinelloxidskikt som minskar effekten av båda nedbrytningarna i sammankopplingarna. Beläggningen appliceras i en kontinuerlig rulle-till-rullningsprocess och sedan pressas sammankopplingsformen in i materialet, tillverkat som Sanergy HT 441 av Sandvik. Mekaniska spänningar orsakar emellertid mikrokrackar som exponerar underlagsmaterialet, vilket kan påverka oxidationsbeteendet negativt.Lyckligtvis kan förbehandlingar uppnå att spinellen diffunderar över korta avstånd och kombineras med element i underlaget och homogeniserar den skyddande effekten. Detta fenomen som kallas självhelande har inte studerats med tillräckligt djup för Sanergy HT 441. Således testades olika serier av temperatur och korta förbehandlingstider, och självhelande egenskaper observerades med hjälp av SEM-ytkarakterisering och kemisk analys. Resultaten indikerar att självläkning kan uppnås inom korta tider med användning av isotermisk förbehandling vid temperaturer över 750 ° C.