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

铝是世界上仅次于钢的第二大使用金属，然而，铝很少以纯金属的形式存在于自然界中。铝确实以氢氧化铝的形式大量存在于地壳中，这种氢氧化铝存在于铝土矿中。这种有着130年历史的方法被称为拜耳（1888）和霍尔-埃鲁（1886）工艺，用于从铝土矿中生产铝，但它是一种高度能源和碳密集型的工业过程。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，显著降低能耗和碳排放的替代工艺将极大地影响铝的经济性和利用率。该学院早期职业发展（CAREER）奖支持研究，以阐明和克服阻碍氢氧化铝在室温下直接转化为铝的基本障碍。这是一种具有通过避免直接碳排放和消除熔化起始和/或中间材料中的能量浪费来改变常规铝熔炼范例的潜力的工艺。除了积极的环境影响外，由于美国使用的大部分铝都是从水力发电便宜的国家进口的，因此本文提出的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，这些活动将向来自宾夕法尼亚州聋人学校的身体残疾学生和来自费城及其周边县的代表性不足的K-12学生展示。氢氧化铝可以在室温下在涉及氢氧根离子并需要电解的方法中电解还原成铝金属。电解质水溶液不幸的是，金属铝与水的高反应性使得使用含水电解质成问题。为了克服这一障碍，正在开发一种创新的混合水/非水电化学电池，并用于在室温下实现氢氧化铝直接电解还原为铝。在还原过程中使用X射线散射技术在真实的时间中研究反应途径，以绘制所产生的铝的尺寸、曲率和晶体结构的演变。同时，将使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扩展性。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识价值和更广泛的影响审查标准进行评估来支持。

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.