One promising way to produce hydrogen with low carbon emissions is to produce hydrogen electrochemically with low carbon intensity electricity. High temperature electrolysis using solid oxide cells offers higher electrical efficiency compared to low temperature electrolysis based on thermodynamics and dynamics of operation. Solid oxide electrolysis cell (SOEC) systems operate across endothermic and exothermic regions which presents additional complexity for thermal management since both heat addition and heat rejection is required depending upon the operating conditions. Due to the unique nature of SOEC systems, development of thermal management strategies for efficient and resilient hydrogen production is essential.

In this dissertation, a thermophysical SOEC system model is developed to assess the dynamic behavior of the SOEC stack and evaluate novel thermal management strategies implemented for the proposed SOEC system. With the proposed SOEC system configuration and thermal control strategies, with diverse cell degradation rates of 5, 7.5 and 10 mΩcm2kh-1, the system can maintain its beginning of life hydrogen production efficiency for at least 9, 6, and 4.5 years, respectively. The efficiency is maintained in the system despite cell degradation because the heat generated by irreversibilities caused by degradation is used by the electrochemical reactions in the immediate vicinity and at the operating temperature, simulating a reversible heat transfer from the electrochemical losses to the water splitting electrochemical reactions themselves.

To evaluate the resiliency of the proposed SOEC system, hot-standby and cold-start operations are investigated. The developed model shows that the proposed system can operate dynamically at very high current density ramp rate of 0.073 A/cm2 per minute in case of an urgent shutdown or start-up to and from hot-standby and can also safely manage the dynamics of a complete shutdown and cold-start operation. The model is further developed to simulate a 3-dimensional SOEC stack and its dynamic performance characteristics. With a 3-dimensional stack model, heater failure scenarios are investigated. To overcome stack heater failure scenarios, increasing inlet air temperature is suggested as the system can operate without large temperature gradients and maintain the system efficiency.

Co-electrolysis emerges as a promising solution for producing the precursor synthesis gas (syngas) for making a variety of hydrocarbons, targeting the integration with sectors of the economy that are difficult to decarbonize. To comprehensively investigate SOECs operating in co-electrolysis mode, an SOEC model is developed which encompasses both electrochemical and thermochemical pathways for CO and H2 (syngas) production from CO2 and water. The model is used to evaluate and compare the performance characteristics of electrolyte-supported and fuel electrode-supported cells. Fuel electrode thickness impacts the reaction pathways in co-electrolysis operation where higher contribution of electrochemical conversion of CO2 is found in thinner fuel electrode SOECs than that of thicker fuel electrode SOECs.

Economic sectors such as transportation, electricity, industrial, commercial, residential, and agriculture depend on a reliable and consistent supply of energy. However, a vast majority of these sectors draw most of their energy from fossil fuels which emit pollutants and greenhouse gases (GHG) when combusted or processed. The emissions, as a result, are the largest contributing factors to recent climate change and environmental challenges. To reduce the emissions using sustainable and renewable energy sources (RES) in the power generating and cement manufacturing sectors, design and integration of a concentrated solar power (CSP) plant with a solid oxide electrolysis cell (SOEC) system for hydrogen production and with a coal-fired cement plant for producing cement are analyzed. To analyze the dynamic behavior, such as temperature variations for thermal management, and system performance characteristics, a dynamic CSP-integrated SOEC system model is developed, aiming to achieve high hydrogen production efficiency and to minimize the balance of plant power consumption. The results show that the electrical efficiency of the integrated hydrogen production system is greater than 90% throughout the majority of the operating time. Particularly, the electrical efficiency between 10 AM and 1 PM is nearly 100%. Such high efficiency is achieved as a result of the SOEC stack operating in endothermic conditions while taking thermal energy provided by the CSP plant. A CSP-integrated cement plant is modeled to assess the percent solarization, reduction in carbon dioxide (CO2) emissions, and costs of CO2 avoided. Five locations have been selected across the United States providing a wide range of Direct Normal Irradiance (DNI) potentials. The results show that the plant located in Southern California (SoCal) has the best performance characteristics with the highest percent solarization and reduction of CO2 emissions, utilizing solar thermal energy more than 70% of the operating time and reducing the CO2 emissions by 15%. Economically, the western region of the United States, especially the states of California, Arizona, Nevada, and New Mexico, is found to be the best region for integrating a conventional cement plant with a CSP plant where the annual DNI exceeds 2000 kWh/m2. The costs of CO2 avoided in the region range from 70 to 100 USD per ton of CO2 which makes such integration as competitive as integration with competing carbon capture technologies.

Dendritic cells are professional antigen presenting cells that activate naïve T cell to promote specific T cell responses. Until recently, the DCs’ recognition of microbial or inflammatory stimuli through PRRs was solely recognized to initiate DCs’ maturation. On the other hand, the role of PRR-independent activation of DCs has remained largely unexplored. This thesis will focus on a recent discovery of cAMP dependent DCs’ maturation. We treated various types of DCs with GPCR ligands and other regulators affecting GPCR/cAMP pathway. Here, we show that DCs’ varying levels of cAMP determine DCs’ ability to promote either Th2 responses or Th17 responses. We discovered that the increased cAMP level reduced the expression of DC’s transcription factors like IRF4 and KLF4. Subsequently, DC’s increased cAMP level reduced Th2 responses and increased Th17 responses. In fact, this cAMP dependent DC maturation is so robust that inducing cAMP signaling alone allowed Th2-promoting DC to switch into Th17-promoting DC. Surprisingly, we discovered that DC’s expression of IRF5 and inhibition of IRF4 are essential in Th17 polarization. In addition, we also described the implication of GPCR/cAMP pathway’s role in the onset of neutrophilic asthma. Th2 response in the airway is known to promote eosinophilic asthma while additional Th17 response induce neutrophilic asthma. Here, we show that a long-term

exposure to asthma’s common bronchodilator, LABA, also switches Th2 mediated eosinophilic asthma into Th17 mediated neutrophilic asthma by elevating DC’s cAMP level. These findings delineate an unforeseen contribution of cAMP signaling in the regulation of innate and adaptive immunity.

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