Bio-Inspired Electroactive Organic Molecules for Aqueous Redox Flow Batteries. 1. Thiophenoquinones

Abstract

Redox flow batteries (RFB) utilizing water-soluble organic redox couples are a new strategy for low-cost, eco-friendly, and durable stationary electrical energy storage. Previous studies have focused on benzoquinones, napthoquinones, and anthraquinones as the electroactive species. Here, we explore a new class of moleculesthiophenoquinonesspecifically focusing on the caldariellaquinone-, sulfolobusquinone-, and benzodithio­phenoquinone-like frameworks that are used for metabolic processes in thermophilic aerobic Sulfolobus archaebacteria. We demonstrated that B3LYP/6-311+G­(d,p) thermochemical calculations (using the SMD solvation model) reproduce experimental reduction potentials to within ±0.04 V. We then studied the effect of amine, hydroxyl, methyl, fluoro, phosphonic acid, sulfonic acid, carboxylic acid, and nitro functional group modifications on the reduction potential and Gibbs energy of solvation in water (using density functional theory) and aqueous solubility (using cheminformatics). Next we enumerated all of the 10 611 possible combinations of functional group substitutions on these frameworks and identified 1056 potential molecules with solubilities exceeding 2 mol/L; of these, 36 molecules have reduction potentials below 0.25 V and 15 molecules above 0.95 V (versus the standard hydrogen electrode (SHE)). The combination of high solubility and wide voltage range makes these molecules promising candidates for high performance aqueous RFB applications. Finally, using our data set of ab initio reduction potentials, we developed a cheminformatics model that predicts ab initio reduction potentials to within ±0.09 V based solely on molecular connectivity. We found that a model trained with as few as 200 examples generates rank-ordered predictions allowed us to identify the highest performance candidates with half the number of ab initio calculations. This offers a strategy for improving the tractability of future computational searches for high performance RFB molecules.

Recent developments in organic redox flow batteries: A critical review

“…Recent research and development in the redox flow battery community has focused on the identification, synthesis and modification of novel redox active molecules [43][44][45][46][47]76].…”

“…Even in the early stages of development, the electrolyte cost of some organic-based flow batteries has been demonstrated to be lower than USD$ 35 (kW h) -1 (based on half-cell estimates) [39][40][41][42]. With advances in synthetic chemistry, the properties of these organic molecules can be further tailored to provide fast kinetics and high solubility, and to yield high cell voltages in batteries [43][44][45][46][47]. The electrolyte cost per kW h can be lowered further by selecting active species based on the cell voltage and/or on multi-electron transfers.…”

Molecular Engineering with Organic Carbonyl Electrode Materials for Advanced Stationary and Redox Flow Rechargeable Batteries

“…However, soluble organic compounds are ideal candidates for RFBs, in which the electroactive species are stored in tanks with circulated liquid electrolyte. [213][214][215][216][217] With such a key difference, RFBs are more durable and scalable than conventional stationary battery systems, making them promising for large-scale applications.…”

Quantum chemistry reveals the thermodynamic principles of redox biochemistry

“…We note that we subtracted the energy of molecular hydrogen (obtained with the same SPE model chemistry) from in order to get redox the E Δ Electronic potentials relative to the standard hydrogen electrode. A similar approach has been used to model redox reactions in the context of organic redox flow batteries 54 .…”