High-Performance Aqueous Organic Flow Battery with Quinone-Based Redox Couples at Both Electrodes

Abstract

We have demonstrated the repeated cycling of a redox flow cell based on water-soluble organic redox couples (ORBAT) at high voltage efficiency, coulombic efficiency and power density. These cells were successfully operated with 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) at the positive electrode and anthraquinone-2,6-disulfonic acid (AQDS) at the negative electrode. Reduction of the voltage losses arising from mass transport limitations, and understanding of the chemical transformations of BQDS during charging have led to these improvements in performance. The specific advances reported here include the use of organic redox couples in the free-acid form, improvements to the flow field configuration, and novel high-surface-area graphite-felt electrode structures. We have identified various steps in the chemical and electrochemical transformations of BQDS during the first few cycles. We have also confirmed that the crossover of the reactants through the membrane was not significant. The performance improvements and new understanding presented here will hasten the development of ORBAT as an inexpensive and sustainable solution for large-scale electrical energy storage. With the increasing penetration of solar photovoltaic and windbased electricity generation, the variable and intermittent output of these energy generation systems is a grave concern for stable operation of the electricity grid. To buffer the inevitable surges in electricity supply and demand, large-scale energy storage systems are needed. Such energy storage systems must be capable of storing thousands of giga-watt hours of electricity per day. Rechargeable batteries are particularly attractive for electrical energy storage because of their high energy efficiency and scalability.1-3 However, for such a largescale application, these batteries must be inexpensive, robust, safe, and sustainable. None of today's commercially-available batteries can meet all the performance and cost targets at this scale of deployment of energy storage. This situation has led to a global search for a transformational solution.In 2013, we described an organic redox flow battery -also known as ORBAT -that uses water-soluble organic redox couples as a safe, scalable, and efficient energy storage system with the potential to meet the United States Department of Energy (DoE) cost target of $100/kWh for large-scale energy storage. 4 In such a battery, aqueous solutions of two different water-soluble organic redox couples -quinones and anthraquinones or their derivatives -were circulated past carbon electrodes in an electrochemical cell. In our current system, the positive electrode is supplied with a solution of 4,5-dihydroxybenzene-1,3-disulfonic acid (BQDS) and the negative electrode uses a solution of anthraquinone-2,6-disulfonic acid (AQDS). The positive and negative electrode compartments are separated by a proton-conducting polymer electrolyte membrane (Figure 1). During charge and discharge, the redox couples undergo rapid proton-coupled electron transfer to store ...

A New Michael-Reaction-Resistant Benzoquinone for Aqueous Organic Redox Flow Batteries

“…The charge and discharge curves at 100 mA/cm 2 showed a single plateau (Figure 7), which is markedly different from that of the BQDS where multiple plateaus were observed from the very first cycle. 21 Furthermore, with BQDS the first discharge only returned one-third of the first charge capacity, consistent with the transformations caused by the Michael reaction, needing three times the amount of charge to reach the final charged state. When DHDMBS was used, the first charge and discharge capacities were almost equal, proving that there was no Michael transformation occurring with DHDMBS.…”

“…13 C NMR chemical shifts were determined relative to the 13 In our previous publication, we demonstrated that changing the starting material from an alkali metal salt to an acid greatly increased its solubility. 21 The acid-form allowed us to reach higher concentration values -as high as 3 M for BQDS and 2 M for AQDS. In turn, this increase in concentration yielded higher operating current densities and improved the overall performance of the cell.…”

“…21 In this cell with BQDS as the positive electrolyte and AQDS as the negative electrolyte, undesired chemical transformations of BQDS occur in addition to the necessary redox reactions. While AQDS is stable and does not undergo such chemical transformations, BQDS undergoes the Michael reaction with water.…”

Comparison of Capacity Retention Rates During Cycling of Quinone-Bromide Flow Batteries

“…Recently, quinones have been demonstrated as inexpensive electroactive species for aqueous flow batteries [2][3][4][5]. One hundred charge-discharge cycles have been demonstrated in an all-quinone flow battery using a tiron posolyte (positive electrolyte) and an anthraquinone-2,6-disulfonic acid negolyte (negative electrolyte), at 35% depth of discharge, with no mention of capacity retention [5].…”

“…One hundred charge-discharge cycles have been demonstrated in an all-quinone flow battery using a tiron posolyte (positive electrolyte) and an anthraquinone-2,6-disulfonic acid negolyte (negative electrolyte), at 35% depth of discharge, with no mention of capacity retention [5]. Our group demonstrated 750 deep cycles of a quinone-bromide flow battery (QBFB) using anthraquinone-2,7-disulfonic acid (AQDS), with 99.84% capacity retention per cycle [6].…”