Silicon Epitaxy by Molten Salt Electrolysis

Author(s): Yi Jie Wu; Sarat Buasai; Alexander McMahon

Advisors: Adam C. Powell; Aaron Deskins; Walter Towner

Category: Undergraduate

The development of solar technology, one of the most dominant renewable energy sources, is critical towards the goal of reaching a fully sustainable future. An increasing demand for solar cells causes an urgent need to produce higher-purity silicon, the main material of new generation cells, at a lower cost. Yet, the dominant Silicon manufacturing method, the Siemens process, is a costly, fuel intensive, and perilous process, resulting in many casualties. The proposed alternative innovation, however, will produce the desired Silicon, directly from Silicon Dioxide (silica). This process will use a molten salt electrolysis process and a novel metal bath, MgF₂-CaF₂-YF₃-CaO-SiO₂, with low viscosity and volatility, as well as high ionic conductivity and SiO2 solubility. The purpose of this project is to study the feasibility of the Molten Salt Electrolysis technology by analyzing the thermodynamics and mass and energy balance of the process, optimizing the performance through cell design, and determining economic viability to scale up the process. The team found that the silicon growth rate on the cathode can reach 1.13 mm/hr at a current density of 1 A/cm2 and an operating temperature of 1100 C°. Each cell unit (1m x 1m x 6.25m) has one rotating cathode tube in the middle surrounded by four 1/4th anodes tubes equidistant apart; the plant design is a network of multiple cell units. The cost analysis shows that a 2 billion dollars capital investment on the technology pilot plant will be able to break even in 11 years by selling the Silicon at $3 per kg, a reduction in the current average price of more than 55%. The silicon production through Molten Salt Electrolysis will allow the process to operate solely on sustainable energy at lower electricity consumption and without any CO₂ emissions, taking the next step towards a sustainable future.

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