(45c) Uncovering Electrolyte Transport Mechanisms in Charged Mxene Membranes Via Continuum Modeling

MXenes are an emerging class of 2D sheet-like nanomaterials. While analogous to the more well-known graphene, what sets them apart is their unique blend of enhanced stability in aqueous media, near-metallic in-plane electrical conductivity, as well as their ability to sustain a surface charge. Membranes composed of layers of MXenes are, thus, promising candidates for next-generation water purification technologies, with the potential for electrostatically tunable ion transport and separation.

Recent experiments by our collaborators in the Noy Group at LLNL confirm that applying a gate voltage to a MXene membrane modulates the resulting transport of electrolytes. Specifically, in a diffusion-driven system, they observe that negative gate voltages lead to lower, saturating ion permeation rates, while positive gate voltages result in higher, increasing permeation rates—a behavior reminiscent of transistors. Additional experiments of the membrane in a pressure-driven system also show that the gate voltage can significantly modulate the magnitude of streaming current.

While prior studies on layered 2D nanomaterial membranes offer qualitative explanations for such phenomena via experiments, a robust, quantitative description grounded in theory continues to remain underdeveloped. To address this gap, we construct a physics-based model of the membrane, capable of accurately predicting its response to an applied gate voltage. Despite the presence of ultrathin nanopores, we adopt a continuum modeling approach, leveraging its unique ability to provide deep physical insights and enable rapid parametric studies. Building on the theory of electrokinetics in nanopores, our work provides the first quantitative look into the physical mechanisms underpinning electrolyte transport in MXene membranes.