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

PI: Pal， Uday机构：波士顿大学受托人提案号：1210442标题：热切：基于固体氧化物膜的太阳能级硅生产电解工艺的可行性这是一个为期一年的早期探索性研究计划，旨在从二氧化硅生产硅。如果成功，它将导致一个更大的研究计划，生产太阳能级硅，并实现太阳能发电1美元/瓦（瓦特峰值）的工业目标，这可能会实现广泛的电网平价。知识优势：这种基于膜的二氧化硅电解工艺将采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。可行性研究将涉及将二氧化硅与一定量的杂质氧化物（如磷、铁和铬的氧化物）溶解在熔融氟化物通量中，并增加电极之间的施加电位，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产生纯氧气，由SOM保护免受熔融助熔剂的影响。为了证明可行性，将进行以下研究活动：-采用适当的熔融氟化物助熔剂系统对二氧化硅进行SOM电解，并控制杂质氧化物的数量。研究将包括使用差热分析、阻抗和热重测量对氟化物通量系统进行调查和选择。-使用简单的电解池设计和适当的参考电极来测量和分析电流响应作为外加电位的函数。这些信息将用于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传递机制。表征金属沉积物（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，将采用多个气体鼓泡管、热电偶和阴极进行更详细的工艺表征，以去除杂质和太阳级硅沉积。将对该矿床的化学和物理性质进行表征，以评估其是否适合太阳级应用。建立SOM电解过程的有限元模型。过程模型将电流密度与传热、流体流动和扩散结合起来，作为过程设计的工具。它将在三维空间运行，并计算边界层结构，以估计浓度极化和传质阻力的变化。其他模型特征将包括确定：使用传质计算的边界层剖面来估计电负性较高和较低的物质以及硅的沉积速率；生长硅阴极的形状演变，以优化电极放置以获得有利的产品形状；除了氩气鼓泡或采用直流磁场等旋转电极外，还提出了新的搅拌方法。通过使用这个模型？MOxST吗?将探索电极的几何形状和位置，以及工艺放大的搅拌条件。更广泛的影响：太阳级硅（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，该工艺有望显著降低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，但该工艺可用于生产其他能源密集型金属（Li, Ti， Al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，增加在电化学处理和能源/环境系统领域的专业知识。我们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，明确招募学生。本科生将通过补充REU提案和BU？S配合奖助金计划。

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.