Sulfonated Diels-Alder Poly(phenylene) Membrane for Efficient Ion-Selective Transport in Aqueous Metalorganic and Organic Redox Flow Batteries

Abstract

Redox flow batteries (RFBs) can achieve long lifetimes and high performance when employing highly selective and conductive membranes. Neutral and alkaline RFBs suffer from higher resistances due to lower cation conductivity, compared to acidic RFBs utilizing proton transport. We report the use of a sulfonated Diels-Alder poly(phenylene) membrane that exhibits low and stable potassium area specific resistance and high efficiency RFB cycling relative to Nafion, as well as undetectable ferricyanide crossover. An alkaline (pH 12) organic anthraquinone derivative RFB using this membrane demonstrates over 10 days of cycling without capacity loss from crossover. A neutral chelated chromium complex RFB using this membrane demonstrates a peak discharge power of 1.23 W cm−2, and 80% energy efficiency cycling at an average discharge power density of 446.3 mW cm−2. Finally, the membrane exhibits similar favorable conductivity for many monovalent cations, opening the opportunity to improve the cycling and crossover performance of other acidic, neutral, and alkaline RFBs.

Membrane–Electrolyte System Approach to Understanding Ionic Conductivity and Crossover in Alkaline Flow Cells

“…The ferrocyanide concentration of the filtrate was determined by UV−vis spectrophotometry and a previously established calibration curve. 50 The filter paper was dried in air, and the mass of the filter paper with filtered precipitates was measured with an analytical balance (METTLER TOLEDO). Figure S3 shows a photograph of an example filter paper from this process.…”

“…But, to the best of our knowledge, only one membrane, a sulfonated poly(phenylene), has matched the undetectable crossover of as-received Nafion NR212 while improving upon its potassium conductivity. 50 We urge that flow battery membrane researchers, especially for aqueous organic RFBs, consider the transport properties of as-received Nafion as more important benchmarks than those of pretreated Nafion. Moreover, we emphasize that the properties of Nafion are extremely pretreatment-dependent, and therefore, all membrane pretreatments should be clearly reported in the main text of manuscripts discussing this material.…”

Planar carbenium ions for robust symmetrical all organic redox flow batteries

“…The working electrode was polished prior to each record using aluminum oxide on polishing paper and anhydrous CH 3 CN to remove residual particles. CVs were recorded at different scan rates (10,25,75,100,250,400, and 500 mV s À1 ) in an CH 3 CN electrolyte solution, containing 1 mM C + and 0.1 M TBAPF 6 .…”

“…The irreversible capacity loss 22 caused by the entropic diffusion of redox-active material throughout the separating interface creates new pathways for chemical deterioration. 23 To reduce active material crossover, a number of methods have been suggested, including improved membrane composition, 24,25 size discrimination methods, 26,27 and also immiscible electrolyte solutions. 28…”

“…The irreversible capacity loss 22 caused by the entropic diffusion of redox-active material throughout the separating interface creates new pathways for chemical deterioration. 23 To reduce active material crossover, a number of methods have been suggested, including improved membrane composition, 24,25 size discrimination methods, 26,27 and also immiscible electrolyte solutions. 28 The design of vanadium redox flow batteries (VRFBs) with almost identical tank composition motivated the emergence of symmetrical Organic RFBs (SORFBs), which are now perceived as the most promising approach to reduce membrane crossover and extend the lifespan of the EES.…”