CAREER: Understanding and Overcoming the Fundamental Barriers to the Direct Reduction of Aluminum Hydroxide to Aluminum Metal

铝是仅次于钢的世界第二大金属，然而，铝在自然界中很少以纯金属的形式存在。铝确实大量存在于地壳中，以氢氧化铝的形式存在于铝土矿中，铝是从铝土矿中提取出来的。这种有130年历史的方法被称为拜耳(Bayer)法(1888)和霍尔-赫鲁特法(Hall-Héroult)(1886)，用于从铝土矿中生产铝，但这是一个能源和碳高度密集的工业过程。生产一公斤铝消耗超过15千瓦时的电能，并释放多达14公斤的二氧化碳。因此，大幅降低能源消耗和碳排放的替代工艺将极大地影响铝的经济和利用率。该学院早期职业发展(CALEAR)奖支持旨在阐明和克服阻碍氢氧化铝在室温下直接转化为铝的根本障碍的研究。这一过程有可能改变传统的铝冶炼模式，避免直接的碳排放，并消除在熔化起始和/或中间材料时的能源浪费。除了对环境的积极影响外，由于美国使用的大部分铝都是从水力发电成本较低的国家进口的，因此这里提出的较低能耗工艺使美国的铝生产更具竞争力，并使美国经济和社会受益。拟议的研究与涉及铝生命周期的各种教育和推广活动相结合，将向宾夕法尼亚聋人学校的肢体残疾学生和费城及其周边国家代表不足的K-12学生展示。从热力学上讲，氢氧化铝可以在室温下被电解成金属铝，这个过程涉及氢氧化物离子，需要水溶液。不幸的是，金属铝与水的高反应性使得水溶液电解液的使用成为问题。为了克服这一障碍，人们正在开发一种新型的水/非水混合电化学池，并将其用于在室温下实现氢氧化铝直接电解还原为铝。用X射线散射技术实时研究了还原过程中的反应路径，绘制了生成的铝的尺寸、曲率和晶体结构的演变图。同时，将利用电化学技术研究反应过电位和界面电荷传输动力学。从电化学测量和基于X射线散射的实时结构表征中获得的基本见解将为工艺优化技术提供信息，以实现最大的氢氧化物到铝的产率和可伸缩性。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

Aluminum is the second most used metal worldwide after steel, however, aluminum rarely exists in nature in the form of pure metal. Aluminum does abundantly exist in the Earth’s crust in the form of aluminum hydroxide found in bauxite ore from which it is extracted. The 130-year-old method, known as the Bayer (1888) and Hall-Héroult (1886) process, is used to produce aluminum from bauxite, but it is a highly energy- and carbon-intensive industrial process. Production of one kilogram of aluminum consumes over 15 kilowatt-hours of electrical energy and releases up to 14 kilograms of carbon dioxide. Therefore, an alternative process that significantly reduces energy consumption and carbon emissions would greatly impact the economy and utilization of aluminum. This Faculty Early Career Development (CAREER) award supports research to elucidate and overcome the fundamental barriers that impede the direct conversion of aluminum hydroxide to aluminum at room temperature. This is a process that has the potential to shift the conventional aluminum smelting paradigm by avoiding direct carbon emissions and eliminating energy waste in melting the starting and/or intermediate materials. Beyond the positive environmental impact, since most of the aluminum used in the U.S. is imported from countries with cheap hydroelectric power, the lower energy-consumption process proposed here allows the U.S. production of aluminum to be more competitive and benefit the U.S. economy and society. The proposed research is integrated with various education and outreach activities involving the aluminum life cycle, which will be showcased to students with physical disabilities from the Pennsylvania School for the Deaf and underrepresented K-12 students from Philadelphia and its surrounding counties.Thermodynamically, aluminum hydroxide can be electrolytically reduced into aluminum metal at room temperature in a process that involves hydroxide ions and requires an aqueous electrolyte. Unfortunately, the high reactivity of metallic aluminum with water renders the use of an aqueous electrolyte problematic. To overcome this obstacle, an innovative hybrid aqueous/nonaqueous electrochemical cell is being developed and used to achieve direct electrolytic reduction of aluminum hydroxide to aluminum at room temperature. The reaction pathways is studied using X-ray scattering techniques in real time during the reduction process to map the evolution of size, curvature and crystal structure of the aluminum created. In parallel, the reaction overpotentials and interfacial charge transport kinetics will be investigated using electrochemical techniques. The fundamental insights gained from electrochemical measurements and real-time structural characterization based on X-ray scattering will inform process optimization techniques to achieve maximum hydroxide-to-aluminum yield and scalability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.