CAREER: Enabling Efficient Separation of Rare-Earth Elements Using Liquid-Metal Bipolar Membranes

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Rare-earth materials are components of renewable energy technologies such as permanent magnet motors for wind turbines and electric vehicles. Despite the critical role of rare-earth materials in the transition to a low-carbon economy, less than 1% of the rare earths are currently recycled. The projected increase in demand for rare earths over the next decade will outpace supply from mined ore. The development of efficient and environmentally-friendly rare-earth recycling techniques is essential for future deployment of clean energy technologies. The goal of this project is to develop an efficient rare-earth element separation using liquid metals as a selective barrier (i.e., a bipolar membrane) that allows rare-earth elements, but not other elements, to pass through when a voltage is applied. This study will test the hypothesis that strong chemical interactions between liquid metals and rare-earth elements will enhance the passage of the rare-earth elements through the bipolar membrane. If successful, the liquid-metal bipolar membrane will provide a way to recycle rare-earth materials from end-of-life products through direct separation in a single electrochemical cell. This will broadly benefit society by reducing the environmental burden associated with rare-earth mining and reliance on energy-intensive rare-earth separation technology. Research and education are integrated by engaging students in fields essential to long-term U.S. economic competitiveness, including electrochemical energy storage, materials synthesis, separation of energy-critical materials, and corrosion-resistant coatings. Graduate and undergraduate students' knowledge of electrochemistry will be cultivated through a holistic curriculum that integrates hands-on research experience with targeted coursework. High school students and STEM educators will be engaged through the "Electrochemistry for Materials Sustainability" outreach program. The program aims to introduce non-experts to the field of electrochemistry, cultivating a curiosity about electrochemistry, its role in solving real-world challenges, and motivating the pursuit of STEM careers.The Principal Investigator's long-term career goal is to enable materials sustainability through the development of energy-efficient separation and recycling technologies. Toward this goal, this project investigates a new electrochemical approach for efficient separation of rare-earth elements, utilizing liquid metals as a bipolar membrane that allows for unique electrochemical reactions and mass transport of rare-earth elements across the liquid-metal bipolar membrane under an electric field. The research objectives for this project are to establish the fundamental thermodynamic, interfacial, and transport properties of a liquid-metal bipolar membrane that govern electrochemical selectivity and permeability for rare earths. The outcomes of the project will include highly accurate thermodynamic, interfacial, and transport properties of rare earths, essential for developing liquid-metal bipolar membranes, as well as development of reliable experimental techniques for their measurement. The experimentally-verified properties will be integrated into the development of computational tools (solution models and first-principles calculations) for simulating atomic bonding, phase equilibria, interfacial kinetics, and atomic diffusion. This approach will accelerate the design of liquid-metal bipolar membranes that possess an exceptional selectivity and permeability for rare earths, enhance the predictive capabilities of computational materials modeling, and advance the current knowledge of rare earths. The scientific approaches developed in this project will serve as a general means for the discovery of superior materials with better control over chemical selectivity for other energy-critical materials beyond rare earths.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.