We introduce a novel Organic Redox Flow Battery (ORBAT), for meeting the demanding requirements of cost, eco-friendliness, and durability for large-scale energy storage. ORBAT employs two different water-soluble organic redox couples on the positive and negative side of a flow battery. Redox couples such as quinones are particularly attractive for this application. No precious metal catalyst is needed because of the fast proton-coupled electron transfer processes. Furthermore, in acid media, the quinones exhibit good chemical stability. These properties render quinone-based redox couples very attractive for high-efficiency metal-free rechargeable batteries. We demonstrate the rechargeability of ORBAT with anthraquinone-2-sulfonic acid or anthraquinone-2,6-disulfonic acid on the negative side, and 1,2-dihydrobenzoquinone-3,5-disulfonic acid on the positive side. The ORBAT cell uses a membrane-electrode assembly configuration similar to that used in polymer electrolyte fuel cells. Such a battery can be charged and discharged multiple times at high faradaic efficiency without any noticeable degradation of performance. We show that solubility and mass transport properties of the reactants and products are paramount to achieving high current densities and high efficiency. The ORBAT configuration presents a unique opportunity for developing an inexpensive and sustainable metal-free rechargeable battery for large-scale electrical energy storage. The integration of electrical energy generated from solar and wind power into the grid is faced with the challenge of intermittent electricity output from these sources. This challenge can be effectively met by storing the electricity during times of excess production and releasing the electrical energy to the grid during times of peak demand. Rechargeable batteries are very attractive for energy storage because of their high energy efficiency and scalability.1-3 Since grid-scale electrical energy storage requires hundreds of gigawatt-hours to be stored, 4 the batteries for this application must be inexpensive, robust, safe and sustainable. None of today's mature battery technologies meet all of these requirements. The vanadium redox flow battery is one such battery technology that has reached an advanced level of development for grid-scale applications.5 However, the limited resources of vanadium, the high expense associated with the cell materials, and the toxicity hazard of using large quantities of soluble vanadium, have been the major challenges to the widespread adoption of the vanadium redox flow battery. 2,6,7 Aiming to overcome these disadvantages, we have demonstrated for the first time an aqueous redox flow battery that uses water-soluble organic redox couples at both electrodes that are metal-free. Such a battery has the potential to meet the demanding cost, durability, eco-friendliness, and sustainability requirements for grid-scale electrical energy storage. We have termed this battery an Organic Redox Flow Battery (ORBAT).In ORBAT, two different aqueous solutions...

Easy to prepare solid materials based on fumed silica impregnated with polyethylenimine (PEI) were found to be superior adsorbents for the capture of carbon dioxide directly from air. During the initial hours of the experiments, these adsorbents effectively scrubbed all the CO(2) from the air despite its very low concentration. The effect of moisture on the adsorption characteristics and capacity was studied at room temperature. Regenerative ability was also determined in a short series of adsorption/desorption cycles.

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 ...

The shuttling of polysulfide ions between the electrodes in a lithium-sulfur battery is a major technical issue limiting the self-discharge and cycle life of this high-energy rechargeable battery. Although there have been attempts to suppress the shuttling process, there has not been a direct measurement of the rate of shuttling. We report here a simple and direct measurement of the rate of the shuttling (that we term "shuttle current"), applicable to the study of any type of lithium-sulfur cell. We demonstrate the effectiveness of this measurement technique using cells with and without lithium nitrate (a widely-used shuttle suppressor additive). We present a phenomenological analysis of the shuttling process and simulate the shuttle currents as a function of the state-of-charge of a cell. We also demonstrate how the rate of decay of the shuttle current can be used to predict the capacity fade in a lithium-sulfur cell due to the shuttle process. We expect that this new ability to directly measure shuttle currents will provide greater insight into the performance differences observed with various additives and electrode modifications that are aimed at suppressing the rate of shuttling of polysulfide ions and increasing the cycle life of lithium-sulfur cells. The rechargeable lithium-sulfur battery is of great interest due to its high theoretical specific energy of 2600 Wh/kg and also the relatively low cost of sulfur. However, large-scale deployment of lithium-sulfur batteries has been limited by several performance issues relating to power density and cycle life. [1][2][3][4][5][6][7][8][9] With sulfur at the positive electrode and lithium metal at the negative electrode, the lithium-sulfur battery operates over a voltage range of 1.5 to 2.8 V. The reactions at the positive and negative electrode during charge and discharge are shown schematically in Figure 1. During discharge, sulfur at the positive electrode is reduced progressively to various polysulfides and eventually to the sulfide, while lithium metal at the negative electrode is oxidized to lithium ions. During charge, the lithium ions are reduced to lithium at the negative electrode, and the sulfide is re-oxidized at the positive electrode to the higher-order polysulfides. The organic electrolyte is a 0.5 M solution of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in a 1:1 mixture by volume of dioxolane (DOL) and dimethoxyethane (DME). A "solid electrolyte interphase" (SEI) protects the lithium anode from reacting freely with the organic electrolyte. The polysulfides produced during discharge are usually soluble in the battery electrolyte. Summary of technical challenges with lithium-sulfur batteries.-The principal challenge for the realization of a practical lithium-sulfur battery with long cycle life arises from the solubility of the higherorder polysulfides (S 8 2− , S 6 2− , S 4 2− ) in the electrolyte. These polysulfides, generated at the positive electrode during discharge, diffuse to the negative lithium electrode where they are reduced to...

Inexpensive, robust and efficient large-scale electrical energy storage systems are vital to the utilization of electricity generated from solar and wind resources. In this regard, the low cost, robustness, and eco-friendliness of aqueous iron-based rechargeable batteries are particularly attractive and compelling. However, wasteful evolution of hydrogen during charging and the inability to discharge at high rates have limited the deployment of iron-based aqueous batteries. We report here new chemical formulations of the rechargeable iron battery electrode to achieve a ten-fold reduction in the hydrogen evolution rate, an unprecedented charging efficiency of 96%, a high specific capacity of 0.3 Ah/g, and a twenty-fold increase in discharge rate capability. We show that modifying high-purity carbonyl iron by in situ electro-deposition of bismuth leads to substantial inhibition of the kinetics of the hydrogen evolution reaction. The in situ formation of conductive iron sulfides mitigates the passivation by iron hydroxide thereby allowing high discharge rates and high specific capacity to be simultaneously achieved. These major performance improvements are crucial to advancing the prospect of a sustainable large-scale energy storage solution based on aqueous iron-based rechargeable batteries. Large-scale electrical energy storage systems are needed to accommodate the intrinsic variability of energy supply from solar and wind resources.1,2 Such energy storage systems will store the excess energy during periods of electricity production, and release the energy during periods of electricity demand. Viable energy storage systems will have to meet the following requirements: (i) low installed-cost of <$100/kWh, (ii) long operating life of over 5000 cycles, (iii) high round-trip energy efficiency of over 80%, and (iv) ease of scalability to megawatt-hour level systems.2 Rechargeable batteries are particularly suitable for such large-scale storage of electrical energy because of their high round-trip efficiency and scalability. Among the types of rechargeable batteries under consideration are vanadium-redox, sodium-sulfur, zinc-bromine, zinc-air and lithium-ion batteries. 3,4 In addressing the challenges of durability, cost, and large-scale implementation of the foregoing types of batteries, the beneficial features of iron-based alkaline batteries for large-scale energy storage have been largely overlooked. Nickel-Iron batteries have been used in various stationary and mobile applications for over 70 years in the USA and Europe until the 1980s when the iron-based batteries were largely supplanted by sealed lead-acid batteries. Iron-air batteries because of their high specific energy underwent active development for electric vehicles and military applications in the 1970s after the "oil shock" but major research in this area was abruptly discontinued after 1984. Except for some seminal research in India by Shukla et al. during the period 1986-1992, iron electrodes have not received any significant attention. [5][6][7] We e...