Benzoquinone-Hydroquinone Couple for Flow Battery
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Benzoquinone-Hydroquinone Couple for Flow Battery Saraf Nawar,1 Brian Huskinson,2 and Michael Aziz2 1 Harvard College, Cambridge, MA 02138, USA 2 Harvard School of Engineering and Applied Sciences, 29 Oxford Street, Cambridge, MA 02138, USA ABSTRACT At present, there is an ongoing search for approaches toward the storage of energy from intermittent renewable sources like wind and solar. Flow batteries have gained attention due to their potential viability for inexpensive storage of large amounts of energy. While the quinone/hydroquinone redox couple is a widely studied redox pair, its application in energy storage has not been widely explored. Because of its high reversibility, low toxicity, and low component costs, we propose the quinone/hydroquinone redox couple as a viable candidate for use in a grid-scale storage device. We have performed single-electrode tests on several quinone/hydroquinone redox couples, achieving current densities exceeding 500 mA/cm2, which is acceptable for use in energy applications. We fabricated a full cell using para-benzoquinone at the positive electrode against a commercial fuel cell hydrogen electrode separated by a Nafion membrane. We evaluated its performance in galvanic mode, where it reached current densities as high as 150 mA/cm2. The results from these studies indicate that the quinone/hydroquinone redox couple is a promising candidate for use in redox flow batteries. INTRODUCTION In recent years, there have been enormous annual increases in wind and solar power generation, and continued rapid increases are anticipated. Because these sources are intermittent, it is becoming crucial to find cost-effective means of grid-scale energy storage, so that the temporal profile of natural supply can be matched to the demand profile. Flow batteries have received recent attention for this purpose, due to our ability to decouple energy and power capacities in their design, thereby allowing for the optimal sizing of Figure 1. Reduction and oxidation each capability independently [1]. They may also mechanism for para-benzoquinone/ hydroquinone couple become competitive with Pb-acid batteries for stationary storage applications such as off-grid storage of photovoltaically generated energy. Nevertheless, it remains a challenge to design a scalable energy storage system permitting very low cost per kWh. The vanadium redox system, which has received the most attention, suffers from a high vanadium market price, which sets a floor on the ultimate capital cost per kWh [2]. We are investigating organic molecule-based electrochemical cells as cost-effective alternatives. In particular, quinones and their derivatives appear to be promising candidates as they offer low cost, low toxicity, and high reversibility in electrochemical reactions. Furthermore, quinones are already ubiquitously found in nature, as
they play an active role in oxygen-evolving photosynthesis as part of the electron-transport chain in photosystem II [3]. Fig. 1 shows the mechanism for the oxidation and reduction of para-benzoqu
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