Abstract
As redox active macromolecules are introduced to the materials repertoire of redox flow batteries (RFBs), nanoporous membranes, such as polymers of intrinsic microporosity (PIMs), are emerging as a viable separation strategy. Although their selectivity has been demonstrated, PIM-based membranes suffer from time-dependent resistance rise in nonaqueous electrolytes. Here, we study this phenomenon as a function of membrane thickness, electrolyte flow rate, and solvent washing using a diagnostic flow cell configuration. We find that the rate and magnitude of resistance rise can be significantly reduced through the combination of low electrolyte flow rate and solvent prewash. Further, our results indicate that, since the increase is not associated with irreversible chemical and structural changes, the membrane performance can be recovered via ex-situ or in-situ solvent washes.
Highlights
Redox flow batteries (RFBs) are a promising technology option for energy-intensive grid storage applications, but cost reductions are needed for broad deployment [1,2]
A recently reported strategy is the application of polymers of intrinsic microporosity (PIMs), which are typically used for gas separations [13], as size-exclusion membranes within electrochemical systems [10,12,14]
Swelling tests (Fig. 1b) evidenced that while water does not readily imbibe into the membrane (0.31 mmol gPIM-1−1), soaking in either ACN or propylene carbonate (PC) leads to significant dimensional changes
Summary
Redox flow batteries (RFBs) are a promising technology option for energy-intensive grid storage applications, but cost reductions are needed for broad deployment [1,2]. In most prior work, tests were performed under conditions where performance decay can be due to confluence of confounding factors (e.g., unstable active species for RFBs, solid-electrolyte-interphase formation for Li-S batteries), which can mask changes in the PIM properties. Continued advancement of this molecular platform requires an understanding of performance-determining factors within device embodiments that mirror intended applications. To this end, we evaluate the impact of electrolyte flow rate, membrane thickness, and pretreatment conditions on the ohmic resistance of a PIM-1 membrane in a single electrolyte flow cell
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