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1. Solid Oxide Membrane (SOM)-Based Technology for Carbon-Free Efficient Production of Solar-Grade Silicon

   Haoxuan Yan; Michelle Sugimoto; Adam Powell; Uday Pal (January 2022, REWAS 2022: Developing Tomorrow’s Technical Cycles (Volume I))

   Lazou, A.; Daehn, K.; Fleuriault, C.; Gökelma, M.; Olivetti, E.; Meskers, C (Ed.)

   State-of-the-art solar-grade silicon production is energy intensive and has a negative impact on the environment. Due to the robust and rapid growth of the Si-based photovoltaic (PV) industry, it is necessary to develop a greener technology for silicon production. Solid oxide membrane (SOM) electrolysis is a proven versatile green technology that can be developed to economically produce many important metal or metal compounds from their oxides. This work will discuss application of SOM electrolysis to produce solar-grade silicon from silica in a single-step resulting in net-zero-carbon emission. The high-temperature SOM electrolysis cell employs stable molten oxide-fluoride bath with silicon wafer cathode and stabilized zirconia membrane-based novel anodes. The cell design and process parameters are selected to enable silicon deposition on the Si wafer cathode. However, initially an electrochemical oxidation reaction occurred between silicon and oxygen that involved the cathode/flux/gas interfaces. An approach to successfully prevent this side reaction has been demonstrated. Electrochemical characterization of the SOM process is presented, and post-experimental characterization demonstrates Si deposits in the form of silicon carbide due to the use of graphite crucible and graphite current collector. 

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2. Macroscopic Modeling and Phase Field Modeling of Solar Grade Silicon by Molten Salt Electrolysis

   Moudgal, Aditya; Asadikiya, Mohammad; Moore, Douglas; Espinosa, Gabriel; Wallace, Lucien; Wadsworth, Alexander; Melo, Tyler; Alonzo, Alexander; Charlebois, Andrew; Costa, Evan; et al (February 2022, REWAS 2022: Energy Technologies and CO2 Management (Volume II))

   Tesfaye, Fiseha; Zhang, Lei; Guillen, Donna Post; Sun, Ziqi; Baba, Alafara Abdullahi; Neelameggham, Neale R.; Zhang, Mingming; Verhulst, Dirk E.; Alam, Shafiq (Ed.)

   DOI: 10.1007/978-3-030-92559-8_5 The sixth Intergovernmental Panel on Climate Change report (IPCC) recently released predicts a deep reduction in emissions to meet global goals of 1.5 °C reduction in temperature. It states that concentrations of CO₂ have continuously increased in the atmosphere reaching averages of 410 ppm in 2019. Therefore, it becomes imperative to reduce CO₂ in any way possible. Silicon, which is an important material for renewable energy, electronics, and metallurgy, is primarily produced by the carbothermic reduction of quartz. This metallurgical grade silicon is then refined by the Siemens Process to solar grade silicon using hydrogen chloride. The by-product of trichlorosilane from this process is highly volatile and unstable. This work aims to achieve the above process of reduction in a single step using electrochemistry. This would eliminate multiple steps and save energy and cost and reduce emissions if a suitable inert anode is used in production. Understanding electrochemical cell characteristics therefore is needed to prove and scale this technology. Macroscopic models help engineers to design, develop, and improve the efficiency of electrochemical cells. They solve conservation equations of mass, momentum, and energy and help determine electrode current distribution, fluid flow, heat distribution, and stability of the cell. They also help in correlating experimental work and understanding measurements in cells from a lab scale to a plant scale. However, they do not predict the microstructure and plating of material on the cathode. This can be calculated using phase field models. These phase field models predict interface stability and deposition morphology in the cell. In this work, we present these models in addition to proof-of-concept experiments. 

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3. Critical Material Applications and Intensities in Clean Energy Technologies

   https://doi.org/10.3390/cleantechnol1010012  

   Leader, Alexandra; Gaustad, Gabrielle (December 2019, Clean Technologies)

   Clean energy technologies have been developed to address the pressing global issue of climate change; however, the functionality of many of these technologies relies on materials that are considered critical. Critical materials are those that have potential vulnerability to supply disruption. In this paper, critical material intensity data from academic articles, government reports, and industry publications are aggregated and presented in a variety of functional units, which vary based on the application of each technology. The clean energy production technologies of gas turbines, direct drive wind turbines, and three types of solar photovoltaics (silicon, CdTe, and CIGS); the low emission mobility technologies of proton exchange membrane fuel cells, permanent-magnet-containing motors, and both nickel metal hydride and Li-ion batteries; and, the energy-efficient lighting devices (CFL, LFL, and LED bulbs) are analyzed. To further explore the role of critical materials in addressing climate change, emissions savings units are also provided to illustrate the potential for greenhouse gas emission reductions per mass of critical material in each of the clean energy production technologies. Results show the comparisons of material use in clean energy technologies under various performance, economic, and environmental based units. 

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4. Membrane distillation at the water-energy nexus: limits, opportunities, and challenges

   https://doi.org/10.1039/C8EE00291F  

   Deshmukh, Akshay; Boo, Chanhee; Karanikola, Vasiliki; Lin, Shihong; Straub, Anthony P.; Tong, Tiezheng; Warsinger, David M.; Elimelech, Menachem (January 2018, Energy & Environmental Science)

   Energy-efficient desalination and water treatment technologies play a critical role in augmenting freshwater resources without placing an excessive strain on limited energy supplies. By desalinating high-salinity waters using low-grade or waste heat, membrane distillation (MD) has the potential to increase sustainable water production, a key facet of the water-energy nexus. However, despite advances in membrane technology and the development of novel process configurations, the viability of MD as an energy-efficient desalination process remains uncertain. In this review, we examine the key challenges facing MD and explore the opportunities for improving MD membranes and system design. We begin by exploring how the energy efficiency of MD is limited by the thermal separation of water and dissolved solutes. We then assess the performance of MD relative to other desalination processes, including reverse osmosis and multi-effect distillation, comparing various metrics including energy efficiency, energy quality, and susceptibility to fouling. By analyzing the impact of membrane properties on the energy efficiency of an MD desalination system, we demonstrate the importance of maximizing porosity and optimizing thickness to minimize energy consumption. We also show how ineffective heat recovery and temperature polarization can limit the energetic performance of MD and how novel process variants seek to reduce these inefficiencies. Fouling, scaling, and wetting can have a significant detrimental impact on MD performance. We outline how novel membrane designs with special surface wettability and process-based fouling control strategies may bolster membrane and process robustness. Finally, we explore applications where MD may be able to outperform established desalination technologies, increasing water production without consuming large amounts of electrical or high-grade thermal energy. We conclude by discussing the outlook for MD desalination, highlighting challenges and key areas for future research and development. 

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5. Exploring the practical efficiency limit of silicon solar cells using thin solar-grade substrates

   https://doi.org/10.1039/d0ta04575f  

   Augusto, A.; Karas, J.; Balaji, P.; Bowden, S. G.; King, R. R. (August 2020, Journal of Materials Chemistry A)

   null (Ed.)

   Multiple silicon solar cell technologies have surpassed or are close to surpassing 26% efficiency. Dielectric and amorphous silicon-based passivation layers combined with minimal metal/silicon contact areas were responsible for reducing the surface saturation current density below 3 fA cm −2 . At open-circuit, in passivated contact solar cells, the recombination is mainly from fundamental mechanisms (Auger and radiative) representing over 3/4 of the total recombination. At the maximum power point, the fundamental recombination fraction can drop to half, as surface and bulk Shockley–Read–Hall step in. As a result, to further increase the performance at the operating point, it is paramount to reduce the bulk dependence and secure proper surface passivation. Bulk recombination can be mitigated either by reducing bulk defect density or by reducing the wafer thickness. We demonstrate that for commercially-viable solar-grade silicon, thinner wafers and surface saturation current densities below 1 fA cm −2 , are required to significantly increase the practical efficiency limit of solar cells up to 0.6% absolute. For a high-quality n-type bulk silicon minority-carrier lifetime of 10 ms, the optimum wafer thickness range is 40–60 μm, a very different value from 110 μm previously calculated assuming undoped substrates and solely Auger and radiative recombination. In this thickness range surface saturation current densities near 0.1 fA cm −2 are required to narrow the gap towards the fundamental efficiency limit. We experimentally demonstrate surface saturation currents below 0.5 fA cm −2 on pi/CZ/in structures across different wafer thicknesses (35–170 μm), with potential to reach open-circuit voltages close to 770 mV and bandgap-voltage offsets near 350 mV. Finally, we use the bandgap-voltage offset as a metric to compare the quality of champion experimental solar cells in the literature, for the most commercially-relevant photovoltaic cell absorbers and architectures. 

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