All-PEGylated redox-active metal-free organic molecules in non-aqueous redox flow battery

Abstract

A non-aqueous redox flow battery based on all-PEGylated, metal-free compounds is presented. The PEGylation enhances the stability of the redox-active materials, alleviating crossover by increasing the anolyte and catholyte species’ molecular sizes.

Azobenzene‐Based Low‐Potential Anolyte for Nonaqueous Organic Redox Flow Batteries

“…The PEG3‐PTZ catholyte with three ethylene glycol units (PEG3) is synthesized following a reported procedure from our group [26] (Figure S2 and Scheme 1). Compared with PEG12‐PTZ with 12 PEG units in our previous study, PEG3‐PTZ has higher neat concentration (3.39 M vs. 1.72 M) [26b] for higher energy density. Odom et al .…”

Dual function organic active materials for nonaqueous redox flow batteries

“…While recent molecular engineering efforts have focused on multi-property optimization to increase active species solubility and stability for high energy density RFBs, 14,16 to date, only a few molecular cores have shown promise as potential active materials, including derivatives of benzoquinone, 20,21 anthraquinone, 18,[22][23][24] nitroxyl radicals, 19,25 dialkoxybenzenes, 26,27 phenazine, 13,17,28 cyclopropeniums, 12,29 pyridiniums, 16,30 viologen,31-35 and phenothiazine. 6,14,35,36 Although a large variety of organic redox couples demonstrate stable cycling in nonaqueous RFBs, in many cases, results were obtained from flow cells operated at low concentrations, 4,26,30,33,36 some of which are a result of limited active species solubility -especially in their charged forms. It is important to evaluate active materials at concentrations used in commercial cells so that performance metrics and limitations can be identified.…”

Bipolar Redox‐Active Molecules in Non‐Aqueous Organic Redox Flow Batteries: Status and Challenges

“…The crossover performance of electroactive materials can be evaluated by their permeabilities (P) using a H-cell. [29] As depicted in Scheme 2a, one chamber of the H-cell, termed the retentate side, is filled with ROM solution; while the permeate side only contains supporting electrolyte. The volumes of the retentate and permeate sides are set to be equal for the balance of osmotic pressure.…”

“…These permeability measurements can be employed to analyze whether ROM structure (e. g., ionic or neutral, [29a] size [29b,c] ), or synthesized membranes [30] reduce the crossover of active species. Notably, this set up simulates the scenario where a RFB has distinct ROMs in each compartment, and only neutral ROMs are present.…”

“…In addition, a second‐electron transfer is achievable, but cycling of these high oxidation states showed significant capacity decay [38] . Permeability is an important factor in evaluating crossover, [29a,c] yet such studies are often absent in the literature. Further, mechanistic studies including charge transport dynamics, decomposition processes and products are still rare.…”