The reduction of manufacturing costs and the facilitation of direct-oxidation of hydrocarbon fuels have been identified as means of promoting the commercialization of the solid oxide fuel cell, a technology that offers both environmental and fuel conservation benefits compared to conventional energy conversion technologies. This research was conducted with the aim of realizing the production of direct-oxidation anodes using atmospheric plasma spraying, which has been identified as a fabrication technique that has the potential to reduce the manufacturing costs of solid oxide fuel cells. This thesis details the rationale behind the selection of the anode compositions (BaO-Ni-YSZ, CeO2-Ni-YSZ, and Sn-Ni-YSZ) and the specifics of the specialized fabrication strategy (SPS-SPPS) that was devised with the aim of realizing microstructures similar to those where the secondary phases (BaO, CeO2, and Sn) coat the surfaces of the primary Ni and YSZ phases. Results of XRD, SEM and EDS analyses are presented.

The reduction of manufacturing costs and the facilitation of direct-oxidation of hydrocarbon fuels have been identified as means of promoting the commercialization of the solid oxide fuel cell, a technology that offers both environmental and fuel conservation benefits compared to conventional energy conversion technologies. This research was conducted with the aim of realizing the production of direct-oxidation anodes using atmospheric plasma spraying, which has been identified as a fabrication technique that has the potential to reduce the manufacturing costs of solid oxide fuel cells. This thesis details the rationale behind the selection of the anode compositions (BaO-Ni-YSZ, CeO2-Ni-YSZ, and Sn-Ni-YSZ) and the specifics of the specialized fabrication strategy (SPS-SPPS) that was devised with the aim of realizing microstructures similar to those where the secondary phases (BaO, CeO2, and Sn) coat the surfaces of the primary Ni and YSZ phases. Results of XRD, SEM and EDS analyses are presented.

A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.

In organischen Leuchtdioden (OLEDs) werden üblicherweise anorganische Materialien wie Indium-Zinn-Oxid (ITO) als transparente leitfähige Anoden verwendet. ITO besitzt allerdings eine geringe Austrittsarbeit und kann deshalb Löcher nicht effizient in organische Materialien injizieren. Weiterhin ist ITO eine Quelle von Indium- und Sauerstoff-Ionen, die in die organischen Materialien diffundieren und dort mit der Organik reagieren bzw. als effiziente Exzitonenvernichter agieren. Eine mögliche Alternative zu ITO sind hoch leitfähige Polymere wie PEDOT:PSS und Polyaniline. Diese Studie untersucht die physikalischen Aspekte von OLEDs mit elektrisch dotierten Ladungstransportschichten auf Polymeranoden. Hierbei werden pin-OLEDs auf ITO mit OLEDs auf Polymeranoden direkt verglichen und mit dem derzeitigen Stand der Technik diskutiert. Die Untersuchungen zeigen, daß OLEDs auf PEDOT:PSS Anoden eine höhere Effizienz erreichen als OLEDs auf ITO Anoden. Um die physikalischen Unterschiede von pin-OLEDs auf ITO und PEDOT:PSS Anoden zu untersuchen, werden optische Simulationen sowie Ultraviolett-Photoemissions-Spektroskopie (UPS) und Lebensdauermessungen durchgeführt. Die optischen Simulationen zeigen, daß die Polymeranoden durch ihren geringen Brechungsindex eine höhere Lichtauskopplungseffizienz besitzen als OLEDs mit einer ITO-Anode. Außerdem finden UPS-Messungen eine geringere Löcherinjektionsbarriere von PEDOT:PSS zu dotierten und undotierten Lochtransportschichten. Aus diesem Grund ist die Ladungsträgerinjektion an der Anoden-Organik-Grenzfläche effizienter, wenn eine PEDOT:PSS-Anode verwendet wird. Lebensdauermessungen von pin-OLEDs auf PEDOT:PSS-Anoden zeigen eine vergleichbare Lebensdauer zu OLEDs auf ITO-Anoden. Die Ergebnisse dieser Untersuchungen zeigen eindeutig, daß Polymeranoden das Potential besitzen, ITO als Anode zu ersetzen und zusätzlich die OLED-Effizienz zu erhöhen.

This dissertation presents findings from two disparate research projects relating to the cathodic protection (CP) of piles supporting bridge elements. The first was a proof of concept study for developing a new hybrid pile repair system incorporating embedded sacrificial zinc anodes within a fiber reinforced polymer (FRP) wrap. The second was to develop and remotely monitor the performance of magnesium anodes protecting steel H-piles supporting two bridges in Florida. The hybrid FRP-CP system involved a proof-of-concept laboratory study to refine pressure / vacuum bagging systems for pile repair and to quantify the improvement in the FRP concrete bond. Two different FRP systems, one epoxy based and the other urethane based, were evaluated. Improvement in bond was determined through destructive pullout tests conducted on full-size pile specimens that were wrapped while partially submerged in a fresh water tank. The results showed that pressure led to significant improvement in FRP-concrete bond. Pressure was optimal for the epoxy-based system, while vacuum proved better for the urethane-based system. The pressure system was subsequently used to install FRP over embedded anodes in a field demonstration project where four corroding piles were repaired using the hybrid FRP-CP system. Cathodic protection was provided by embedding eight zinc anodes in each concrete pile. Protection below the water line was provided by bulk anodes. Reference electrodes were installed to monitor the performance of the CP system and data loggers were used to monitor the anodic current. Results from over 12 months of monitoring showed that the hybrid FRP-CP system worked and the current demand of the steel was lower in the FRP wrapped piles compared to the unwrapped control. Numerical simulations were carried out to determine how the hybrid FRP-CP system could be improved. Initially the investigation focused on determining if bulk anodes alone could be used to provide the required protection. Results showed that while bulk anodes were more effective in FRP wrapped piles, they could not provide adequate protection over the entire splash-zone. In view of this, a preliminary three dimensional finite element analysis was carried out using commercially available software. The analysis showed that anode strips embedded in the pile just beneath the surface may provide adequate protection. Such anodes would be easier to install and are an improvement over the system investigated. The second project involved the development of a remote monitoring system to assess the performance of a sacrificial anode cathodic protection system used for steel piles on two bridges along I-75 in Florida. The problem was the inexplicable consumption rate of the magnesium anodes. Commercially available systems and sensors were used to successfully monitor the environment and the anodic current of the CP system for over 12 months. A solution for the excess magnesium consumption was proposed through the incorporation of an in-circuit variable resistor that could regulate the current draw from the anode. The system was implemented but its performance will be monitored by the Florida Department of Transportation who assumed responsibility for the equipment. Initial results were promising.

High fuel utilization SOFCs could eliminate emissions from systems that include afterburners and potentially be suitable for carbon sequestration, while producing electricity more efficiently. Current fuel utilization operating points are typically chosen at approximately 85% for Ni-cermet anodes because higher fuel utilization frequently results in the formation of nickel oxide and reduces drastically the performance of the SOFC. In this work the feasibility of an in-plane graded anode architecture with a transition from a material with high catalytic activity to materials more stable under high fuel utilization conditions was evaluated through a steady-state SOFC finite element model. Thereafter, plasma spraying of solution precursor feedstock (SPPS) and suspension feedstock (SPS) was used to fabricate ceramic coatings that could potentially be used as SOFC anodes for high fuel utilization conditions. Microstructural, electrical and electrochemical properties of LST, LSBT and LSFCr coatings with additions of carbon black pore former were investigated.

High fuel utilization SOFCs could eliminate emissions from systems that include afterburners and potentially be suitable for carbon sequestration, while producing electricity more efficiently. Current fuel utilization operating points are typically chosen at approximately 85% for Ni-cermet anodes because higher fuel utilization frequently results in the formation of nickel oxide and reduces drastically the performance of the SOFC. In this work the feasibility of an in-plane graded anode architecture with a transition from a material with high catalytic activity to materials more stable under high fuel utilization conditions was evaluated through a steady-state SOFC finite element model. Thereafter, plasma spraying of solution precursor feedstock (SPPS) and suspension feedstock (SPS) was used to fabricate ceramic coatings that could potentially be used as SOFC anodes for high fuel utilization conditions. Microstructural, electrical and electrochemical properties of LST, LSBT and LSFCr coatings with additions of carbon black pore former were investigated.

No description available.

Solid oxide fuel cells (SOFCs) are promising power generation devices due to its high efficiency and low pollutant emissions. SOFCs operate with a wide range of fuels from hydrogen (H2) to hydrocarbons, and are mainly intended for stationary power generation. Compared to combustion systems, SOFCs have significantly lower environmental impacts. However, the full scale commercialization of SOFCs is impeded by high cost and problems associated with long-term performance and durability. The cell performance can be affected by various internal losses, involving cathode, anode and electrolyte. Anodic losses make a significant contribution to the overall losses, practically in anode-supported cells. Therefore, it is desirable to reduce the anodic losses in order to enhance the overall cell performance. Knowledge of the actual elementary reaction steps and kinetics of electrochemical reactions taking place on the anode is critical for further improvement of the anode performance. Since H2 and carbon monoxide (CO) are the primary reforming products when hydrocarbons are used as SOFC fuels, investigation of electrochemical reactions involving H2 and CO should provide a better understanding of SOFC electrochemical behavior with hydrocarbon feeds. However, still exist uncertainties concerning both H2 and CO electrochemical reactions. The overall objective of this research is to investigate the mechanistic details of H2 and CO electrochemical reactions on SOFC anodes. To achieve this objective, Ni/YSZ pattern anodes were used in the experimental study and as model anodes for the simulation work due to their simplified 2-D structure. The Ni/YSZ pattern anodes were fabricated using a bi-layer resist lift-off method. Imaging resist nLOF2035 and sacrificial resist PGMI SF11 were found to be effective in the bi-layer photolithographic process. Suitable undercut size was found critical for successful pattern fabrication. A simple method, involving taking microscopic photographs of photoresist pattern was developed, to check if the undercut size is large enough for the lift-off; semi-circle wrinkles observable in photographs indicate whether the undercut is big enough for successful pattern anode fabrication. The final product prepared by this method showed straight and clear Ni patterns. A systematic study was performed to determine the stable conditions for Ni/YSZ pattern anode performance. The microstructure and electrochemical behavior changes of the pattern anode were evaluated as a function of Ni thickness, temperature and H2O content in H2 environment. Ni/YSZ pattern anodes with 0.5 µm thick Ni were tested in dry H2 at 550°C without significantly changing the TPB line. Ni/YSZ pattern anodes with Ni thickness of 0.8 µm were tested at 550°C under dry and humidified H2 (3-70% H2O) conditions without TPB line change. For 0.8 µm thick patterns, the TPB length showed pronounced changes in the presence of H2 with 3-70% H2O at 700°C. Significant increase in TPB length due to hole formation was observed at 800°C with 3% and 10% H2O. Ni/YSZ pattern anodes with 1.0 µm thick Ni were stable in H2 with 3% H2O in the range 500-800°C, with only slight changes in the TPB line. Changes of TPB line and Ni microstructure were observed in the presence of 3-70% H2O above 700C. Stabilization of the pattern anode performance depends on temperature. To accelerate stabilization of the cell, pre-treatment of the cell in H2 with 3% H2O for ~22 hrs at 750°C or 800°C could be performed. In addition, comprehensive data sets for H2 and CO electrochemical oxidation reactions on Ni/YSZ pattern anodes were obtained under stable test conditions. For the H2/H2O system, the polarization resistance (Rp) increases as temperature, overpotential, H2 partial pressure, TPB length decreases. Rp is also dependent on H2O content. When the H2O content is between 3% and 30-40%, Rp decreased with increasing H2O content. However, Rp is less affected with further increases in H2O content. For the CO/CO2 system, polarization resistance depends on partial pressure of CO and CO2, temperature and overpotential. Moreover, the polarization resistance decreases when the partial pressure of CO2 and temperature increase. The partial pressure of CO has a positive effect on the polarization resistance. The polarization resistance decreases to a minimum when the overpotential is 0.1 V. For both H2 and CO electrochemical oxidations, charge transfer reactions contribute to the rate limiting steps. A 1-D dynamic SOFC half-cell model considering multiple elementary reaction kinetics was developed. The model describes elementary chemical reactions, electrochemical reactions and surface diffusion on Ni/YSZ pattern anodes. A new charge transfer reactions mechanism proposed by Shishkin and Ziegler (2010) based on Density Functional Theory (DFT) was investigated through kinetic modeling and pattern anode experimental validation. This new mechanism considers hydrogen oxidation at the interface of Ni and YSZ. It involves a hydrogen atom reacting with the oxygen ions bound to both Ni and YSZ to produce hydroxyl (charge transfer reaction 1), which then reacts with the other hydrogen atom to form water (charge transfer reaction 2). The predictive capability of this reaction mechanism to represent our experimental results was evaluated. The simulated Tafel plots were compared with our experimental data for a wide range of H2 and H2O partial pressures and at different temperatures. Good agreements between simulations and experimental results were obtained. Charge transfer reaction 1 was found to be rate-determining under cathodic polarization. Under anodic polarization, a change in rate-limiting process from charge transfer reaction 1 to charge transfer reaction 2 was found when increasing the H2O partial pressure. Surface diffusion was not found to affect the H2 electrochemical performance.

A series of cermet powders of composition NixCo(1-x)O-YSZ were synthesized for testing as cermet anode materials for SOFCs. The Co is found by powder XRD to become incorporated into the crystal lattice of the NiO, thus forming a true alloyed material. SEM and EDS results show two types of particles upon sintering to 1380oC: small, amorphous particles of YSZ and large, crystalline particles of nickel. The electrochemical oxidation of hydrogen on a cermet anode composed of Ni0.7Co0.3O-YSZ was investigated using a series of many button cells. Through EIS data, cyclic voltammetry data, the exchange current densities for these button cells were determined. Although a relatively large variation was found (expected to be due to microstructural variation) the average values for both methods of measurement is in good agreement in hydrogen. Following reduction in pure hydrogen, the fuel was changed to a mixture with high concentration of H2S. It was found that a concentration of 10 % H2S/H2 produced a sudden change in anode microstructure and resulted in loss of exchange current density. Lowering the amount of H2S in the initial fuel feed, which allowed for a more gradual microstructural change, allowed the cell to eventually function at concentrations in excess of 10 % H2S/H2. It was determined by OCV values in various concentrations of H2S/H2 that hydrogen is the predominant fuel of choice, even if H2S is available. Following electrochemical testing, slow cooling in a 10 % H2S/H2 mixture following produced metal sulfide spheres, as determined by SEM and EDS. Investigation in hydrocarbon, alcohol and biodiesel fuels was then undertaken to test the fuel variability of the given cermet anode material. Methane containing 10 % H2S was found to have increased exchange current density relative to poisoned hydrogen. Ethane and biodiesel experienced no increase in exchange current density, but a lengthening of the functional lifetime of the cell was observed, indicating reduced carbon poisoning. Methanol is a promising oxygen-containing SOFC fuel since it produced exchange current density values larger than hydrogen, and showed no evidence of coke formation by post-mortem SEM. Since oxygen-containing fuels are known to decompose in the gas phase at typical SOFC operating temperatures, the performance in a mixture of various CO/H2 fuels was then investigated. The Ni0.7Co0.3O-YSZ cermet anode gave higher exchange current density values for low ratio of CO/H2 fuels in the range 20/80 and 30/70 compared to pure H2. This is the first example of a Ni-based anode providing higher performance with a CO/H2 mixed fuel than for a pure H2 fuel. Finally, continuous running of a cell with fuel ratio 25/75 CO/H2 for 7 days produced exchange current density values, which were observed to increase significantly above the values for pure H2 during days 1-4 followed by deterioration below the value for hydrogen on subsequent days.