| Solid oxide fuel cell (SOFC) is an energy conversion device with very high efficiency and very low environmental pollution. It has a great positive role on the economizing of energy and environment protection. For the whole system efficiency and commercialization of SOFC, it’s critical to directly use hydrocarbon fuels such as methane directly. To achieve this target, we need to develop anode material with high carbon deposition resistance.The aim of this thesis is to achieve the above target. In this work, a brief review of SOFC technology and material requirements is firstly presented. A series of experimental work were carried out. Sr2FeMoO6(SFMO), NiO-Sm0.2Ce0.8O3(SDC) and Sn-NiO-SDC anode materials have been developed and used in methane fueled SOFCs. Experiments and thermodynamic calculations have been done to figure out the influence of output current on the stability of SOFCs.Study of SFMO double perovskite anode materials. SFMO was synthesized via a combined citrate and EDTA complexing method, electrolyte supported SFMO|La0.8Sr0.2Ga0.83Mg0.17O3(LSGM)|Ba0.5Sr0.5Co0.8Fe0.2O3(BSCF) single cells were prepared by screen printing technology. Results indicate that SFMO has a good chemical and thermal compatibility with LSGM. XPS characterization results confirm the existence of multiple valence pairs in the B side of double perovskite structure. In H2fuel, the single cell exhibits maximum power densities (Pmax) of863.8,603.2and435.6mW cm-2at850,800and750oC, respectively. In CH4fuel, the Pmax is604.8and429.1mW cm-2for850and800oC. In CH4fuel, the cell performance only drops about6.1%and5.7%at850and800oC after20testing cycles.Development of NiO-SDC anode materials. In chapter3, High oxygen ion conductivity material SDC was combined with NiO and used in SOFCs. Results indicate the Pmax of anode supported NiO-SDC|SDC|BSCF single cell in H2fuel achieves624.46,518.91and353.50mW/cm2at700,650and600oC, respectively. While at the above temperatures, the Pmax in CH4fuel is671.24,494.12and305.42mW/cm2. The durability tests were carried out by operation the cell under a300mA constant output current at600oC, and only3.7%performance drop was observed during the72h operation. High resolution SEM characterization on the tested cell anode surface indicates the existence of small amount of carbon deposition, mainly formed on the Ni surface and Ni-SDC interface. The TPO-MS analyses on the grounded anode-electrolyte bilayer powder suggest there are four kinds of carbon deposits with different oxidation temperature. The poorly polymerized, H-rich coke on Ni surface is the dominating part. Results also show the total amount of coke is increasing with increasing operation time.Study of Sn-NiO-SDC anode materials. In chapter4, Sn-NiO-SDC materials with different Sn loading were prepared by incipient wetness technique. Characterization indicates after reduction, Sn can form surface alloy with Ni. TPR data show the introducing of Sn decrease the reduction temperature of NiO-SDC. Results show the performance of single cell in H2and CH4both decrease with the increase of Sn loading. But from the stability test results, introducing Sn into NiO-SDC can improve the stability and inhibit the coke formation.Research about the effect of single cell output current on the stability under CH4fuel. In chapter5, experiments and thermodynamic calculations were combined to investigate the influence of output current on the stability. We found the stability is improved by increasing the output current. Meanwhile, from the calculation results, we found the coke formation rate is increasing with increasing temperature under low current condition, but reversed under high current condition. Data also show that increasing the local concentration of H2O and CO2near the reaction site can improve the carbon deposition resistance. |
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