EAGER: Feasibility of the Solid Oxide Membrane-Based Electrolysis Process for Solar Grade Silicon Production

PI：PAL，Uday Institution：波士顿大学的托管人提案编号：1210442标题：EIGER：基于固体氧化物薄膜的电解太阳能级硅生产工艺这是一个为期一年的早期探索性研究计划，旨在从二氧化硅中生产硅。如果成功，这将导致一个生产太阳能级硅的更大的研究计划，并实现太阳能发电的工业目标，即1美元/WP(峰值暴露时的瓦特)，这可能使广泛的电网并网发电。智能优点：这种基于膜的二氧化硅电解工艺将使用固体氧离子导电膜(SOM)，如稳定的氧化锆，来电解二氧化硅和其他杂质氧化物。可行性研究将包括将二氧化硅与受控数量的杂质氧化物(如P、Fe和Cr氧化物)溶解在熔融的氟化物熔剂中，并增加电极之间的外加电势，以首先沉积更多的电负性杂质，然后在阴极沉积纯硅。电解过程中的阳极反应将在惰性阳极上产生纯氧气气体，由SOM保护，使其不受熔融熔剂的影响。为了证明可行性，将进行以下研究活动：-使用适当的熔融氟化物熔剂系统进行SOM电解二氧化硅，并控制杂质氧化物的数量。研究将包括使用差热分析、阻抗和热重测量来调查和选择氟化物助熔剂系统。&amp；#56256；&amp；#56440；-使用带有适当参考电极的简单电解槽设计来测量和分析作为施加电势的函数的电流响应。这些信息将被用来模拟系统中由于化学扩散、迁移和对流而产生的传质阻力，并了解沉积过程中的电荷转移机制。-表征金属沉积层(硅)的微观结构和化学成分，并将其与工艺模型联系起来。在该计划的下一阶段，将使用多个气泡管、热电偶和阴极进行更详细的工艺表征，以去除杂质和太阳能级硅沉积。将对矿床的化学和物理性质进行表征，以评估其适用于太阳能级应用。建立了SOM电解过程的有限元模型。该工艺模型将电流密度与传热学、流体流动和扩散相结合，作为工艺设计的工具。它将在三个维度上运行，并计算边界层结构，以估计浓度极化和传质阻力的变化。其他模型功能将包括确定：使用来自传质计算的边界层轮廓来估计电负性较大和较少的物种以及硅的沉积速率的多物种沉积；生长的硅阴极的形状演变，以优化电极布置以获得有利的产品形态；除吹氩或旋转电极外的新的搅拌方法，如使用直流磁场。通过使用该模型：MOxST？将探索电极几何形状和位置，以及工艺扩大的搅拌条件。广泛影响：太阳能级硅(SOG-Si)占太阳能电池成本的很大一部分。与目前使用的硅生产方法相比，这一工艺有望显著降低SOG-Si的成本，减少温室气体(GHG)，并提高能源效率。虽然这项研究的重点是SOG-Si，但该工艺也可用于生产其他能源密集型金属(锂、钛、铝等)，从而提高整体能源效率并减少温室气体排放。该项目将为两名研究生提供研究机会，增加电化学加工和能源/环境系统领域的专业知识。学生将通过与代表性不足的学生组织合作，以及通过我们与霍华德大学的联系来明确招收。本科生将通过补充REU提案和北大-S配对助学金计划得到支持。

PI: Pal, Uday Institution: Trustees of Boston UniversityProposal Number: 1210442Title: EAGER: Feasibility of the Solid Oxide Membrane-Based ElectrolysisProcess for Solar Grade Silicon ProductionThis is a one-year early-stage exploratory research program aimed at producing silicon from silica. If successful, it will lead to a larger research program producing solar grade silicon and achieving the industrial goal for solar power of $1/Wp (watt at peak exposure) which could enable widespread grid parity.Intellectual Merit: This membrane-based silica electrolysis process will employ a solid oxygen-ion conducting membrane (SOM), such as stabilized zirconia, to electrolyze silica and other impurity oxides. The feasibility studies will involve dissolving silicon dioxide with controlled amounts of impurity oxides (such as those of P, Fe and Cr) in a molten fluoride flux and increasing the applied electrical potential between the electrodes to first deposit more electronegative impurities, followed by the deposition of pure Si at the cathode. The anodic reaction during the electrolysis process will produce pure oxygen gas at an inert anode, protected from the molten flux by the SOM.In order to demonstrate feasibility, the following research activities will be undertaken:- Employ appropriate molten fluoride flux system for performing SOM electrolysis of silica with controlled amounts of impurity oxides. Research will include survey and selection of the fluoride flux systems using differential thermal analysis, impedance and thermo-gravimetric measurements.�� - Use a simple electrolysis cell design with appropriate reference electrodes to measure and analyze current response as a function of the applied electrical potential. This information will be used to model mass-transfer resistance in the system due to chemical diffusion, migration and convection and understand the charge-transfer mechanism during the deposition process.- Characterize the microstructure and chemical composition of the metal deposit (silicon) and relate it to the process model. In the next phase of the program, more detailed process characterization employing multiple gas bubbling tubes, thermocouples and cathodes will be performed for impurity removal and solar grade silicon deposition. The chemical and physical properties of the deposit will be characterized to assess its suitability for solar grade application. A finite element SOM electrolysis process model will be developed. The process model will combine electric current density with heat transfer, fluid flow, and diffusion for use as a tool for process design. It will run in three dimensions, and calculate boundary layer structures in order to estimate changes in concentration polarizations and mass transfer resistances. Other model features will include determining: multiple species deposition using boundary layer profiles from mass transfer calculations to estimate deposition rates for more- and less-electronegative species as well as for silicon; shape evolution of the growing silicon cathode in order to optimize electrode placement for favorable product form; new stirring methods in addition to argon bubbling or rotating electrodes such as employing DC magnetic field. By using this model ?MOxST? will explore electrode geometry and placements, and stirring conditions for process scaleup.Broader Impact: Solar-grade silicon (SoG-Si) represents a large fraction of the cost of solar cells. This process is expected to significantly lower the cost of SoG-Si, reduce Green House Gases (GHG), and increase energy efficiency compared to the currently used methods of silicon production. While this study is focused on SoG-Si, the process can be used for production of other energy-intensive metals (Li, Ti, Al, etc.), leading to increased overall energy efficiency and reductions in GHG emissions. The project will provide research opportunities for two graduate students, increasing expertise in the areas of electrochemical processing and energy/environmental systems. Students will be explicitly recruited by working in conjunction with under-represented student organizations, and through our contacts with Howard University. Undergraduates will be supported through a supplementary REU proposal and through BU?s matching grant programs.