Collaborative Research: DMREF: Rational design of redox-responsive materials for critical element separations

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Non-technical Description: Rare-earth elements and platinum group metals are critical elements for applications ranging from smartphones and light-emitting-diode (LED) lights to green energy technologies. Other countries mine and process most of the world’s REE supply. US mines can contribute to 15% of the world’s annual supply of rare-earth elements. However, US mines produce mixtures of these elements, which cannot be used in applications until they are separated from one another. This program will develop sustainable strategies for separating and recovering rare-earth elements and platinum group metals from waste streams. This project will utilize electrically-driven separations to separate these valuable elements. This approach is modular, reversible, minimize waste, and can be driven by renewable sources. Electrode materials that bind these elements will be developed from conductive polymers and carbon nanotubes. Beyond contributing to the critical materials economy, the knowledge gained can be applied to other challenging separations, like removing heavy metals and toxic contaminants from water. This project will also help educate and cultivate a diverse future workforce with key competencies in data science, computation, and experiments. New educational content will be released, students will be trained on advanced materials topics, and K-12 outreach programs will be implemented. Technical Description: Electrochemical charge-transfer materials have been proposed as new-generation technologies for separation processes, including water desalination, critical element recovery, and remediation of toxic contaminants. Electrically-driven systems offer significant advantages such as integration with renewable energy, elimination of secondary pollutants or regeneration chemicals by being solely electrochemically regenerable, and modularity. However, recovery of platinum group metals (PGMs) and rare-earth elements (REEs) is a significant challenge for separations science because these elements are found as dilute ions in the presence of excess levels of competing species and with complex speciation depending on pH and ion concentration – and the applicability of electroseparations to REEs and PGMs is severely limited by the fundamental lack of molecular selectivity. This program will develop and implement efficient electrochemical systems for REE and PGM recovery by discovering new polymer-based electrode materials with innovative adsorbate–ion interaction modes, which provide highly selective yet reversible binding. Though typical design approaches employ energy storage materials or use trial­and­error, where machine learning (ML) trained on molecular dynamics (MD) simulations and experimental data will guide chemical selection, synthesis, and electrode ink creation to produce ion-selective yet processable redox­polymers. The simultaneous design of molecular binding and polymer secondary structure in a closed­loop can help accelerate downstream deployment of advanced redox­materials. MD­guided selection of polymer backbones and solvents that maximize ink stability, paired with advanced rheology and coating processes, will enable the creation of electrosorbents with desired macroscopic properties through scaleup, overcoming solubility and processing challenges typical of redox­polymers. Iteration between computation and experiments will produce a framework for rationally designing redox electrodes that, in addition to addressing critical element mixtures of direct relevance to mining and critical materials recycling, can be extended to address challenges in water desalination and environmental remediation.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.