Development and Optimization of High Temperature Electrolysis Pathways to Produce Carbon, Calcium Oxide, and Ammonia Using Molten Salt Electrolytes
Open AccessHigh temperature electrolysis reactions are a viable route for CO2 free production of a variety of societal staples. The studies in this dissertation will demonstrate the ability to capture and transform CO2 to produce valuable carbon products at electrolysis potentials less than 1V at high current densities and with non-noble metal electrodes. Additionally, the resulting carbon product can be tailored to specific nanostructures by controlling the metal nucleation sites present at the electrode, the amount of metal oxide available in the electrolyte, and by altering the current density of the electrolysis. A molten carbonate electrolyzer has the potential to act as a CO2 capture and transformation technology. An electrolysis CO2 transformation technology is an improvement to conventional carbon capture sequestration technology due to the fact that the product produced can be several times more valuable as well as being highly stable, allowing for easy storage. Thermodynamically, the energy required for such a process can capture and transform all the CO2 from a combined cycle natural gas power plant, while still producing electricity. An alternative pathway for the production of lime is presented by taking advantage of the solubility difference between calcium carbonate and calcium oxide in lithium carbonate. Proceeding in a molten carbonate system, the limestone (CaCO3) is electrolyzed into a solid carbon product, oxygen, and calcium oxide. With no CO2 emissions being released, this pathway allows for the production of a green cement that is needed for the future. A third electrolysis pathway for the production of ammonia through high temperature electrolysis in molten hydroxides is also presented using a simple nano-iron catalyst and non-noble metal electrodes. The process has been shown to have a high coulombic efficiency (< 30%), while requiring a potential of 1.23V. A high-pressure configuration of this system demonstrated a decrease in voltage and an increase in coulombic efficiency. Utilizing a novel solar pressurizing design, this configuration is able to be performed using only solar energy creating an entirely CO2 free pathway for the production of ammonia.A high temperature electrolysis system has been shown to have very high solar to product efficiency, as a result of the ability to utilize the entire spectrum of solar energy. A mobile outdoor system was capable of capturing atmospheric CO2 and transforming it into a solid carbon product. By utilizing concentrated solar thermal energy, the system was able to maintain an electrolyte in excess of 750°C, while driving an electrolyzer with a concentrated photovoltaic. Additionally, the entire system was based off of readily available commercial parts demonstrating the maturity of the technology required to implement a high temperature electrolysis. These three electrolysis pathways utilize high temperature molten salt chemistries to perform high rate, low energy, and CO2-free electrolysis reactions to produce important societal staples.
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