Fuel cell is one of the most promising clean energy and alternative energy technologies due to its advantages of low emissions and high efficiency. One application of the fuel cell technology is onboard auxiliary power units (APUs) for power generation in aircrafts, ships, and automobiles. In order to supply hydrogen or syngas for the fuel cell APUs, onboard fuel processing technology was proposed to convert hydrocarbon fuels into syngas through reforming reactions. Two major tasks need to be completed in onboard fuel processing technology. Firstly sulfur compounds have to be removed from hydrocarbon fuels because sulfur can cause reforming catalyst deactivation and fuel cell electrodes poisoning problems. Secondly hydrogen and carbon monoxide shall be produced by reforming of hydrocarbon fuels at a high energy conversion efficiency. This dissertation focused on onboard fuel processing of Jet-A fuel to produce hydrogen and syngas for solid oxide fuel cell (SOFC) APUs. Jet-A fuel was studied because it is the logistic fuel commonly used for civilian airplanes and military heavy duty trucks. Ultra-deep adsorptive desulfurization of Jet-A fuel from over 1,000 ppmw to below 50 ppmw, and autothermal reforming of n-dodecane as a Jet-A fuel surrogate as well as the real desulfurized Jet-A fuel to produce syngas have been systematically investigated in the present study. For the adsorptive desulfurization of Jet-A fuel, a novel NiO-CeO₂/A1₂O₃-SiO₂ adsorbent was proposed and prepared in-house for experimental tests. The sulfur adsorption kinetic characteristic and isotherm at equilibrium were studied in batch tests, and the dynamic desulfurization performance of the adsorbent was investigated in fixed bed tests. Fixed bed tests operation conditions including liquid hourly space velocity (LHSV), adsorbent particle size, and fixed bed dimensions were optimized to achieve the highest adsorbent sulfur adsorption capacity. For the reforming of Jet-A fuel, autothermal reforming (ATR) method was employed and a bimetallic NiO-Rh catalyst was synthesized for the ATR reactions. A lab-scale 2.5 kWt autothermal reforming system including the reformer and balance-of-plant was designed, fabricated, integrated and tested. The reforming system performances at various operation conditions were compared. Reformer operation temperature, steam to carbon ratio and oxygen to carbon ratio, as well as pre-heating temperatures for fuel, air and steam were optimized based on system energy conversion efficiency, H₂ selectivity and COₓ selectivity.

Solid oxide fuel cells (SOFCs) that operate directly on hydrocarbon fuels eliminate the requirement for costly and complex external reforming systems. Atmospheric plasma spraying (APS) is an established manufacturing method that offers the potential to fabricate direct oxidation SOFC anodes in a single step, instead of the multiple steps currently required. Manufacturing by APS also allows the use of metal supports, which improve thermal shock resistance, allow rapid cell heat-up, and reduce total cost. In this study, direct oxidation SOFC anodes based on Cu and samaria-doped ceria (SDC) in combination with Co and/or Ni were investigated for their stability and performance in H2 and CH4 when plasma sprayed on ferritic stainless steel supports. Several different APS techniques were investigated. Two of these techniques were hybrid methods involving a combination of dry powder plasma spray and suspension plasma spray (SPS) processes. These techniques were proposed to help balance the degree of melting of the lower melting temperature oxides of the metals Cu, Co, and Ni with that of the higher melting temperature SDC. The use of a single suspension containing all of the anode component feedstocks was also investigated. Multi-component aqueous suspensions of CuO, Co3O4, and NiO were developed with or without the addition of carbon black and SDC. It was found that the use of a hybrid plasma spray technique can help to improve deposition efficiency (D.E.) and enhance partial melting of the low melting temperature feedstocks. However, plasma spraying all of the components in a single suspension can lead to more homogeneous mixing and greater resistance to metal coarsening at SOFC operating temperatures. In electrochemical tests of plasma-sprayed metal-supported cells containing these anodes, peak power densities as high as 0.6 W/cm2 were achieved at 750 deg C in humidified H2. In CH4, power density was limited by the activity of the anodes. Stability in CH4 was poor because of oxidation of the metal support and enhanced coking behaviour resulting from interactions between Fe in the support and Co and Ni in the anodes. When separated from the supports, the anodes demonstrated very low coking rates in thermogravimetric analysis experiments in CH4.

Solid oxide fuel cells (SOFCs) that operate directly on hydrocarbon fuels eliminate the requirement for costly and complex external reforming systems. Atmospheric plasma spraying (APS) is an established manufacturing method that offers the potential to fabricate direct oxidation SOFC anodes in a single step, instead of the multiple steps currently required. Manufacturing by APS also allows the use of metal supports, which improve thermal shock resistance, allow rapid cell heat-up, and reduce total cost. In this study, direct oxidation SOFC anodes based on Cu and samaria-doped ceria (SDC) in combination with Co and/or Ni were investigated for their stability and performance in H2 and CH4 when plasma sprayed on ferritic stainless steel supports. Several different APS techniques were investigated. Two of these techniques were hybrid methods involving a combination of dry powder plasma spray and suspension plasma spray (SPS) processes. These techniques were proposed to help balance the degree of melting of the lower melting temperature oxides of the metals Cu, Co, and Ni with that of the higher melting temperature SDC. The use of a single suspension containing all of the anode component feedstocks was also investigated. Multi-component aqueous suspensions of CuO, Co3O4, and NiO were developed with or without the addition of carbon black and SDC. It was found that the use of a hybrid plasma spray technique can help to improve deposition efficiency (D.E.) and enhance partial melting of the low melting temperature feedstocks. However, plasma spraying all of the components in a single suspension can lead to more homogeneous mixing and greater resistance to metal coarsening at SOFC operating temperatures. In electrochemical tests of plasma-sprayed metal-supported cells containing these anodes, peak power densities as high as 0.6 W/cm2 were achieved at 750 deg C in humidified H2. In CH4, power density was limited by the activity of the anodes. Stability in CH4 was poor because of oxidation of the metal support and enhanced coking behaviour resulting from interactions between Fe in the support and Co and Ni in the anodes. When separated from the supports, the anodes demonstrated very low coking rates in thermogravimetric analysis experiments in CH4.

A new reactor and a novel in-situ sampling technique were developed for the study of the synthesis of Ce02 powders produced from dissolved cerium nitrate salts. The reactor minimized particle recirculation and provided a highly symmetric and undisturbed plasma flow suitable for the analysis of the phenomena affecting the formation of Ce02 powders. The sampling probe provided in-situ sampling of in-flight CeCb particles and allowed continuous sampling without cross contamination. The sampled particles were collected using a wet collection system composed of a mist atomizer acting as a scrubber and a custom-made spray chamber. The entire collection system is portable and it was tested in the particle range of 20 nm to 100 jam. This information provided a picture of how Ce02 particles were formed. A numerical simulation of different plasma operating parameters using Fluent was presented. A comprehensive droplet-to-particle formation mechanism was deduced based on calorimetry. thermodynamics of Ce02 formation, numerical simulations and collected particles. The effect of adding water soluble fuels (alanine and glycine) to the original cerium nitrate solutions was investigated. Fuel addition decreased the temperature of CeC>2 formation by acting as a local heat source as a result of fuel auto-ignition. The addition of fuel caused “particle size discrimination’*, and a single mode particle size distribution centered between 50-140 nm was achieved along the centerline of the reactor. [...] / Un nouveau reacteur et une technique innovatrice d’echantillonnage in situ furent developpes pour etudier la synthese de poudres de Ce02 produites a partir de sels de nitrate de cerium dissous. Le reacteur minimise la recirculation des particules et fournit un plasma non perturbe et grandement symetrique approprie pour l’analyse des phenomenes affectant la formation de poudres de Ce02. De plus, une sonde permet un echantillonnage in situ et en vol des particules de Ce02 et ce, en continu et sans contamination croisee. Les particules ainsi captees sont recueillies grace a un systeme de collecte par voie humide qui est compose d’un atomiseur de brume (mist atomizer) qui joue le role d’un recureur (scrubber) et d’une chambre d’atomisation (spray chamber) maison. Le systeme d’echantillonnage est mobile et fut teste sur des particules ayant des tailles de 20 nm a 100 jam. C’est grace a l’analyse des particules ainsi recueillies que nous sommes en mesure de comprendre comment les particules de Ce02 sont formees. Nous presentons aussi une simulation numerique, effectuee avec le logiciel Fluent, qui utilise les differents parametres d’experimentation. Le mecanisme detaille de la formation des particules a partir de gouttelettes fut deduit grace a des etudes calorimetriques, a une etude thermodynamique de la formation du Ce02, a des simulations numeriques et a l’analyse des particules recueillies. Nous avons aussi etudie l’effet d’un ajout de combustibles hydrosolubles (l’alanine et la glycine) a la solution originale de nitrate de cerium. Cette addition de combustibles diminue la temperature de formation du Ce02 en agissant comme une source locale de chaleur resultant de 1’auto-ignition du combustible. Aussi, le combustible cause une « segregation des particules » selon leur taille.

Solid oxide fuel cells (SOFCs) conventionally operate between 800 and 1000°C. The barriers for full-scale commercialization of SOFCs are the high cost and relatively poor long-term stability due to the high temperatures used in current state-of-the-art SOFCs. One solution is to decrease the operating temperature, e.g. to 550-750°C but this requires developing new electrolytes and electrode materials. Also, to increase efficiency and practicality, the anode should be able to internally reform hydrocarbon fuels especially methane because it is the most common hydrocarbon in natural gas. The overall goal of this research is to develop a coke-tolerant Ni1-x-yCuxMgyO-SDC anode for methane fuelled IT-SOFCs. The Ni-Cu-Mg-O-SDC anode has been chosen based on the premises that doped-ceria is suitable for intermediate operating temperatures (550-800°C), Ni is known as an active metal and good electronic conductor, Cu increases resistance to coking, MgO helps prevent agglomeration of Ni during reduction, and finally SDC improves oxide ion transport to the cell at this intermediate temperature range. In this work, these materials were characterized in three primary ways: material physical and chemical properties, methane steam reforming activity and electrochemical performance. Two different methods have been used to add Cu to Ni1-yMgyO: a one-step co-precipitation method and a two-step co-precipitation/impregnation method. For the first method, Ni1-x-yCuxMgyO was synthesized via co-precipitation of Ni, Mg and Cu. In the two-step method, Ni0.9Mg0.1O was first prepared by co-precipitation, followed by addition of copper to Ni0.9Mg0.1O by impregnation. However, co-precipitation of all metal in one step limits the sintering temperature of the anode in the cell fabrication due to the low boiling point of CuO. Therefore, co-precipitation of Cu is not a practical method and only Cu impregnation should be considered for practical SOFC applications. It was found that the addition of Mg (Ni0.9Mg0.1O) lowers the reducibility of NiO. Addition of Cu to Ni0.9Mg0.1O up to 5% shows similar reducibility as Ni0.9Mg0.1O. The reducibility of Ni1-x-yCuxMgyO becomes lower when the Cu content is increased to 10%. Nonetheless, all materials are fully reduced at 750ºC. The XRD patterns of pure NiO, Ni0.9Mg0.1O, and the Cu-containing material when Cu is less than 10 mol% are similar. The lower reducibility of Ni-Mg-O and Ni-Cu-Mg-O compared to NiO indicates that they form a solid solution with NiO as the matrix. Solid oxide fuel cells (SOFCs) conventionally operate between 800 and 1000°C. The barriers for full-scale commercialization of SOFCs are the high cost and relatively poor long-term stability due to the high temperatures used in current state-of-the-art SOFCs. One solution is to decrease the operating temperature, e.g. to 550-750°C but this requires developing new electrolytes and electrode materials. Also, to increase efficiency and practicality, the anode should be able to internally reform hydrocarbon fuels especially methane because it is the most common hydrocarbon in natural gas. The overall goal of this research is to develop a coke-tolerant Ni1-x-yCuxMgyO-SDC anode for methane fuelled IT-SOFCs. The Ni-Cu-Mg-O-SDC anode has been chosen based on the premises that doped-ceria is suitable for intermediate operating temperatures (550-800°C), Ni is known as an active metal and good electronic conductor, Cu increases resistance to coking, MgO helps prevent agglomeration of Ni during reduction, and finally SDC improves oxide ion transport to the cell at this intermediate temperature range. In this work, these materials were characterized in three primary ways: material physical and chemical properties, methane steam reforming activity and electrochemical performance. Two different methods have been used to add Cu to Ni1-yMgyO: a one-step co-precipitation method and a two-step co-precipitation/impregnation method. For the first method, Ni1-x-yCuxMgyO was synthesized via co-precipitation of Ni, Mg and Cu. In the two-step method, Ni0.9Mg0.1O was first prepared by co-precipitation, followed by addition of copper to Ni0.9Mg0.1O by impregnation. However, co-precipitation of all metal in one step limits the sintering temperature of the anode in the cell fabrication due to the low boiling point of CuO. Therefore, co-precipitation of Cu is not a practical method and only Cu impregnation should be considered for practical SOFC applications. It was found that the addition of Mg (Ni0.9Mg0.1O) lowers the reducibility of NiO. Addition of Cu to Ni0.9Mg0.1O up to 5% shows similar reducibility as Ni0.9Mg0.1O. The reducibility of Ni1-x-yCuxMgyO becomes lower when the Cu content is increased to 10%. Nonetheless, all materials are fully reduced at 750ºC. The XRD patterns of pure NiO, Ni0.9Mg0.1O, and the Cu-containing material when Cu is less than 10 mol% are similar. The lower reducibility of Ni-Mg-O and Ni-Cu-Mg-O compared to NiO indicates that they form a solid solution with NiO as the matrix. Addition of Mg also lowers the BET specific surface area from 11.5 m2/g for NiO:SDC to 10.4 m2/g for Ni0.9Mg0.1O. The surface area is further reduced when Cu is added; for example, at 10% Cu, the surface area is 8.2 m2/g. The activity of 50wt% Ni1-x-yCuxMgyO/50wt% SDC samples for methane steam reforming (SMR) and water-gas-shift reaction (WGS) was evaluated in a fully automated catalytic fixed-bed reactor where the exiting gases were analyzed online by a gas chromatograph (GC). The tests were performed at steam-to-carbon ratios (S/C) of 3, 2 and 1, and at temperatures of 750°C and 650°C for twenty hours. Higher methane conversions were obtained at the higher temperature and higher S/C ratio. Higher methane conversion are obtained using NiO:SDC and Ni0.9Mg0.1O:SDC than Ni-Cu-Mg-O. The conversion decreases with increasing Cu content. Over NiO:SDC and Ni0.9Mg0.1O:SDC the methane conversions are the same; for example 85% at 750°C for S/C of 3. At the same conditions, impregnation of 5%Cu and 10%Cu yields lower conversions: 62% and 48%, respectively. The activity for the WGS reaction was determined by mornitoring CO2/(CO+CO2) ratio. As expected because WGS is a moderately exothermic reaction, this ratio decreases when increasing the temperature. However, the CO2/(CO+CO2) ratio increases with higher S/C. The results indicate that adding Mg does not affect the WGS activity of NiO. The WGS activity of Ni0.9Mg0.1O:SDC is higher when Cu is added. The effect of additional Cu is more pronounced at 650ºC. At 750°C, changing the amount of Cu does not change the WGS activity because the WGS reaction rapidly reaches equilibrium at this high temperature. At 750°C for S/C of 1, carbon filaments were found in all samples. At 650ºC, different types of deposited carbon were observed: carbon fibers and thin graphite layers. Spent NiO:SDC had the longest carbon fibers. Addition of Mg significantly reduced the formation of carbon fibers. Impregnating 5% Cu on Ni0.9Mg0.1O:SDC did not change the type of deposited carbon. Monitoring the amount of deposited carbon on Ni0.9Mg0.1O:SDC, 3%Cu and 5%Cu impregnated on Ni0.9Mg0.1O:SDC for S/C of 0 at 750ºC showed that Cu addition deactivated methane cracking causing a reduction in the amount of carbon deposited. Electrochemical performance in the presence of dry and humidified hydrogen was determined at 600, 650, 700 and 750ºC. Electrolyte-supported cells constructed with four different anodes were tested using polarization curve and electrochemical impedance spectra. The four anodes were NiO:SDC, Ni0.9Mg0.1O:SDC, 3%Cu and 5%Cu on Ni0.9Mg0.1O:SDC. Adding Mg improved the maximum power density from 356 mW.cm-2 with NiO:SDC to 369 mW.cm-2 with Ni0.9Mg0.1O:SDC at 750ºC in dry hydrogen. Addition of Cu, on the other hand, lowered the maximum power density to 325 mW.cm-2 with 3%Cu impregnated and to 303 mW.cm-2 with 5% Cu impregnated. The cell with Ni0.9Mg0.1O:SDC was also tested under dry methane. To minimize methane cracking under this extreme condition, a current density of 0.10 A.cm-2 was always drawn when methane was present in the feed. The voltage decreased during the first hour from 0.8 to 0.5 V, then remained stable for 10 hours, and then started to drop again. Many small cracks were observed on the anode after completion of the electrochemical test, but there was no evidence of much carbon being deposited. In addition to dry methane, tests were also carried out, using the same material, with a H2O/CH4 mixture of 1/6 in order to generate a polarization curve at 750°C. Under these conditions, the maximum power density was 226 mW.cm-2. This is lower than the maximum power density obtained with humidified hydrogen, which was 362 mW.cm-2.

In this work, numerical and experimental methods are used to characterise the effects of convective transport in an anode-supported tubular solid oxide fuel cell (SOFC). To that end, a computational fluid dynamics (CFD) model is developed to compare a full transport model to one that assumes convection is negligible. Between these two approaches, the variations of mass, temperature, and electrochemical performance are compared. Preliminary findings show that convection serves to reduce the penetration of hydrogen into the anode, and becomes more important as the thickness of the anode increases. The importance of the permeability of SOFC electrodes on the characterization of convection is also investigated. Experiments performed on Ni-YSZ anodes reveal that permeability is a function of the cell operating conditions, and increases with increasing Knudsen number. An empirical Klinkenberg relation is validated and proposed to more accurately represent the permeability of electrodes in a CFD model. This is a departure from an assumption of constant permeability that is often seen in the literature. It is found that a varying permeability has significant effects on pressure variation in the cell, although according to the electrochemical model developed in this work, variation in permeability is only found to have minor effects on the predicted performance. Furthermore, it is revealed that an electrochemical model which makes the simplifying assumption of constant overpotential is in error when predicting current and temperature variation. In this work, this is found to predict an unrealistic spatial variation of the current. It is suggested that this approach be abandoned for the solution of a transport equation for potential which couples the anodic and cathodic currents. This will lead to a more realistic prediction of temperature and performance. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2008-11-04 13:54:35.743

No description available.

No description available.

No description available.

No description available.