Authors: Alejandra C, Acevedo Montano | Yang Huang | Shuai Tan | Andrew Ritchhart | Josiah C. Wray | Manh‐Thuong Nguyen | Grant E. Johnson | Venkateshkumar Prabhakaran
Source: ECS Meeting Abstracts (article, 2025-11-24)
Field: Materials Science — Materials Chemistry

Multielectron Redox-Mediated Separation of Rare Earth Elements at Polyoxometalate-Functionalized Electrodes The selective extraction of rare earth elements (REEs) is essential for advanced technologies in national security, energy, high-performance electronics, and catalysis. The main challenge to selectively separating lanthanides is the chemical similarity of these ions, which exhibit nearly identical charge, size, and hydration. These similarities make conventional separation methods like solvent extraction both energy-inefficient and chemically intensive. As the demand for REEs increases and supply chains become tighter, it is increasingly important to develop precise, low-waste, and energy-efficient separations. Recent innovations in electrochemical REE separations have shown that alternating current and redox-coupled approaches enable selective ion recovery from complex feedstocks by leveraging subtle differences in electron-transfer kinetics, hydration shell structure, or interfacial affinity. However, current electrochemical separation strategies are often limited by single-electron transfer mechanisms or kinetically driven precipitation phenomena, which fail to sufficiently discriminate among neighboring lanthanides. These limitations hinder the precise modulation of ion-binding thermodynamics and redox-coupled coordination behavior, restricting adaptability across the full lanthanide series. Addressing this knowledge gap requires systems capable of stable, multielectron redox control to fine-tune selectivity and reversibility at the molecular level. In this work, we address this challenge by employing a redox-mediated separation approach based on polyoxometalates (POMs) - a class of multielectron, redox-active metal-oxides that offer high structural stability, well-defined redox transitions, and tunable proton-coupled electron transfer properties ( Figure 1 ). Keggin-type phosphotungstic acid POMs were covalently immobilized onto carbon nanotube electrodes using nitrogen-containing organic linker molecules, forming a hybrid electrode with redox-tunable cation coordination sites. This functionalized electrode interface enables selective adsorption and desorption of REEs with electrochemical potential control. A representative subset of lanthanide cations - La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Dy³⁺, and Yb³⁺—was selected to investigate trends in coordination selectivity across the series. Cyclic voltammetry and electrochemical impedance spectroscopy were used to quantify the charge transfer resistance as a function of REE identity and applied potential, revealing distinct interfacial behavior that reflects both cation-specific binding and redox accessibility ( Figure 1 ). Spectroscopic methods, including Raman, ultraviolet-visible absorbance, and X-ray photoelectron spectroscopy, confirmed the formation of reversible inner-sphere coordination complexes and tracked changes in the redox states during ion adsorption and desorption. To complement the experimental measurements, molecular dynamics calculations were employed to elucidate the atomistic configurations and electrostatic interactions within polyoxometalate (POM)–lanthanide complexes. These findings reveal that proton-coupled electron transfer in the POM plays a decisive role in modulating REE affinity and selectivity. Overall, this work demonstrates that multielectron redox-active electrodes enable enhanced control over interfacial chemistry and ion transport, allowing precise tuning of selectivity in electrochemical REE separations. This approach provides a scalable platform for future separations driven by molecular-level tunability, supporting the broader transition toward efficient and selective recovery of critical materials from domestic feedstocks. Figure 1 Lanthanide ; Electrochemistry ; Electron transfer ; Redox ; Electrode ; Extraction (chemistry) ; Adsorption ; Coordination complex Polyoxometalates: Synthesis and Applications ; Iron oxide chemistry and applications ; Extraction and Separation Processes