Molecular Engineering Strategies for Symmetric Aqueous Organic Redox Flow Batteries

Abstract

Symmetric aqueous organic redox flow batteries (RFBs) are potentially an inexpensive, durable, and safe energy storage technology. Unlike normal asymmetric flow batteries, they are based on electrolytes that exist in at least three oxidation states and can undergo a minimum of two distinct redox processes. We compute the redox potentials of selected electrolytes, with the intent to understand how the interaction between the redox units affects the potentials. We find that electronic interaction between redox units and intramolecular hydrogen bonding can be exploited to tune the difference between the redox potentials, i.e., the theoretical voltage of the battery. The redox potentials can be further fine-tuned in either direction by adding substituents. Starting from these observations, we formulate a set of rules that will help in finding ideal candidates for symmetric RFBs.

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

“…A potential pitfall of this strategy is that if the molecules are not functionalized from natural compounds, preparing such artificial structures can be very synthetically challenging. To date, this concept has been illustrated by Fornari et al [45] They outlined 35 electron donoracceptor pairs on two aromatic rings and further connected on a compact molecular core. The redox potentials were computed and compared to their single-redox counterparts -the molecules that only possess one of the redox motifs.…”

“…[59] However, the effectiveness of these mixed electrolytes as compared to BRMs in battery performance remains to be discussed. For example, the solubility of BRMs was computed and found to be higher than their single redox counterparts, [45] yet this still requires experimental evidence. Because the presence of supporting electrolytes decreases the solubility limits of ROMs in solution, [26] adding catholyte into anolyte or vice versa in theory also decreases the maximum concentration of ROMs.…”

Bipolar Organic Polymer for High Performance Symmetric Aqueous Proton Battery

“…[24,25] Among these, bipolar-type organic molecules, which can simultaneously serve as electron acceptor (n-type) and donor (p-type), are particularly attractive to construct organic symmetrical batteries due to the simplified fabrication process and low cost. [26][27][28] However, the difficulty in designing bipolar-type organic compounds is the selection of suitable functional groups to perform different functions. Quinones with n-type functional group, which can achieve fast two H + uptake/removal, have been used as anode for APBs.…”

A Computational Protocol Combining DFT and Cheminformatics for Prediction of pH-Dependent Redox Potentials

“…27,28 The relationship between intramolecular hydrogen bonding and stability has been reported before. 10,29 Calculation of the redox potential at pH 0. For a general proton-coupled reduction reaction Ox +…”

“…One of the main motivations for benchmarking such predictions is the computational screening of the vast chemical space of organic molecules to identify electrolytes for redox flow batteries (RFBs). [1][2][3][4][5][6][7][8][9][10][11][12][13] At some point in any computational workflow for materials discovery, one needs a reliable method to predict with reasonable accuracy and moderate computational cost the properties of an already pre-selected candidate pool. The redox potential is one of the most important properties of redox-active materials.…”