(722b) Ligand-Functionalized Polymer Membranes for Battery Sustainability

Upcycling battery waste into pristine materials simultaneously resolves pressing challenges for sourcing critical metals and managing hazardous waste streams. Electrochemical membrane reactors present a potential route to separating dissolved metal ions directly from battery leachate, but are limited by the poor selectivity of available membrane materials. Moreover, explicit design principles for engineering membranes to favor one ion over another remain obscured, especially when the ions of interest exhibit similar size, valency, and electronic structure.

In this presentation, I explore highly tunable polymer membranes comprising poly(ethylene glycol) dimethacrylate networks with grafted ion-binding moieties (i.e. ligands) of varying coordinating power. Surveying a representative subset of charged and uncharged polymer-bound functional groups reveals that heterocyclic L-type ligands are uniquely capable of distinguishing transition metals, resulting from the formation of transient dative-covalent bonds which in turn direct competitive sorption and diffusion. Fine-tuning ligand frontier orbital energies with electronic donating or withdrawing substituents emerges as a powerful knob for regulating metal ion permeation rates, which may follow or defy the periodic trends commonly invoked to rationalize permeation behavior (e.g., ionic radius and hydration energy). I further interrogate the coordination structure of permeating metal species with vibrational spectroscopy and synchrotron measurements, gaining additional insights into the dynamics of permeating species, which change substantially as a consequence of feed composition and device operating conditions. I conclude with a discussion of the opportunities and limitations for applying design principles established in known molecular organometallic complexes to ion-selective membranes in emerging clean energy technologies, considering urgent needs in critical metal extraction and advanced separators for rechargeable batteries.