Toward an Inexpensive Aqueous Polysulfide–Polyiodide Redox Flow

Jul 3, 2017 - His research focuses on the development and system-level analysis of cost-effective aqueous redox flow batteries for large-scale energy ...
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Toward an Inexpensive Aqueous Polysulfide−Polyiodide Redox Flow Battery Liang Su,†,‡ Andres F. Badel,‡ Changsu Cao,‡,§ Jesse J. Hinricher,‡ and Fikile R. Brushett*,†,‡ †

Joint Center for Energy Storage Research, Argonne National Laboratory, Argonne, Illinois 60439, United States Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States

‡

S Supporting Information *

ABSTRACT: Redox flow batteries (RFBs) hold promise for large-scale energy storage to facilitate the penetration of intermittent renewable resources and enhance the efficiency of nonrenewable energy processes in the evolving electric power system. While all vanadium redox flow batteries (VRFBs) represent the current state-of-the-art, their system price is near 4-fold higher than the price targets outlined by the U.S. Department of Energy, inspiring research into cost reduction through increased energy density or reduced materials cost contributions. Motivated by the abundance and low cost of sulfur and iodine, herein, we explore the feasibility of an aqueous flow battery system using a polysulfide negative electrolyte and polyiodide positive electrolyte. The polysulfide−polyiodide flow battery (SIFB) has an open circuit voltage of 1 V and uses Na+ as the working ion to balance the charge in each electrolyte. Both positive and negative electrolytes display coulombic efficiency close to 100%. Without significant system optimization, the SIFB gives a peak power of 65 mW/cm2 and consistent cycling performance for more than 200 cycles (ca. 530 h) with a stabilized energy efficiency of ca. 50%. Techno-economic analysis shows that the proposed SIFB has the potential to achieve lower prices than the VRFB and to meet the established price targets, but further research is needed with a particular focus on reducing the power cost contributions and developing ion-exchange membranes with improved conductivity and species selectivity.

1. INTRODUCTION Electrochemical energy storage is emerging as a critical technology to enable sustainable electricity generation by alleviating intermittency from renewable sources, reducing transmission congestion, enhancing grid resiliency, and decoupling generation from demand.1−3 As of 2010, pumped hydroelectric storage (PHS) accounted for ca. 99% of the overall worldwide storage capacity, due in part to its high technology readiness level and cost competitiveness.4,5 However, geographic and environmental constraints limit the applicability of PHS to emerging needs and necessitate the development of alternative storage technologies. Redox flow batteries (RFBs) are rechargeable electrochemical devices that hold promise for storing megawatt hours (MWh) of electrical energy on the multihour (h) time scale and at the low system prices needed for economic viability. In a typical RFB, charge-storing active species are dissolved in liquid electrolytes, which are stored in tanks. The electrolytes are pumped through an electrochemical stack, where the active species undergo a reduction or oxidation reaction on the porous electrode surfaces to charge or discharge the battery. Often referred to as the positive and negative electrolyte based on their respective redox potentials, the two electrolytes are separated within the stack by a selective membrane, which enables ion transfer to balance charge but blocks the transport of other compounds, such as the active species and solvents. Compared to enclosed batteries, flow batteries have several key advantages that are particularly relevant to grid storage including © XXXX American Chemical Society

decoupled power and energy scaling, long operational lifetimes, easy maintenance, simplified manufacturing, high active-toinactive materials ratio (particularly at long storage durations), and improved safety characteristics.3,6,7 While numerous flow battery chemistries have been proposed, only a few technologies have been demonstrated at scale and none have experienced widespread commercial success due to technical and economic challenges.8 In recent years, the U.S. Department of Energy (DOE) has established target prices for energy storage systems that reflect the low cost of electricity in the country. Notably, the Office of Electricity Delivery and Energy Reliability set a long-term target of $150/kWh for a fully integrated 4 h discharge energy storage system, including installation and power conditioning equipment.9 The Advanced Research Projects Agency−Energy (ARPA-E) suggested a long-term system cost of $100/kWh.10 However, current price estimates are significantly higher than these targets. For example, all-vanadium redox flow battery (VRFB) systems, arguably the most advanced flow battery technology, are on the order of $400−500/kWh.11−13 Despite this, recent work has established that pathways exist for flow batteries to meet (and even surpass) these targets, either through Received: Revised: Accepted: Published: A

April 10, 2017 June 26, 2017 July 3, 2017 July 3, 2017 DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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cell design, acidic chemistries typically exhibit lower resistance than near neutral or alkaline chemistries, because of the high mobility of protons through liquid electrolytes and solid Nafion.29,33 Consequently, at a system level, the chemical cost savings may be offset by higher reactor costs, which, in turn, impact the economic viability of the proposed technology. Thus, we investigate a similar flow battery chemistry, based on sodium polysulfide and sodium polyiodide, with a particular focus on connecting measured electrolyte and cell performance characteristics to system-level techno-economic assessment. In addition to quantifying the tradeoffs between chemical and reactor costs, we highlight key challenges with this particular system that must be overcome to realize the promise of inexpensive energy storage.

increased energy density or reduced materials cost contributions.7,14 In the context of aqueous RFBs, both organic15,16 and inorganic17,18 active compounds composed of highly abundant elements have shown promise. Note that this low system price must be achieved without compromising safety, scalability, or durability. Pursuant to this goal, we aim to identify new, or previously overlooked, inexpensive active materials with high abundance and low toxicity, which, in turn, may enable energy storage at prices well below the trajectory of current leading technologies. Here, we evaluate the feasibility of a low-cost aqueous flow battery based on a polysulfide negative electrolyte and a polyiodide positive electrolyte. Widely available as an undesired byproduct of natural gas and petroleum refining, sulfur holds promise as a charge storage material. High-temperature molten sodium−sulfur batteries have long been considered for stationary applications,19 and, more recently, nonaqueous lithium−sulfur batteries have been investigated as high-energy-density replacements for lithium-ion batteries in mobile applications.20 Sulfur also holds promise for flow batteries as polysulfides (Sn2−) can be dissolved in both aqueous and nonaqueous electrolytes at high concentrations. Indeed, polysulfide solubility is a confounding factor in nonaqueous lithium−sulfur batteries as the irreversible loss of active sulfur leads to capacity fade. Since their inception in the 1980s,21 polysulfide-based flow batteries have been sporadically investigated, typically in conjunction with a bromine/ bromide couple as the positive electrolyte.22−24 Notably, research and development efforts on polysulfide-bromine RFB culminated in the construction of the 12 MW/100 MWh Little Barford Regenesys plant in the United Kingdom, which, however, was ultimately never realized.25 While attractive from a performance and cost perspective, there are significant safety concerns associated with the bromine/bromide couple including high toxicity (0.1 ppm of OSHA Permissible Exposure Limit26) and high vapor pressure (28.8 kPa at 25 °C27). The iodine/iodide couple presents a promising alternative because of its improved safety characteristics, high aqueous solubility, and potential for low cost via high crustal abundance, albeit at a lower redox potential than that of bromine/bromide couple. Indeed, polyiodide-based electrolytes have been previously proposed in hybrid flow batteries coupled with zinc17 or protected lithium negative electrodes.28 Together, these redox couples result in a polysulfide and polyiodide flow battery (SIFB) with a theoretical equilibrium cell voltage of 0.99 V.29,30

2. EXPERIMENTAL SECTION 2.1. Chemicals. Sodium sulfide (Na2S, anhydrous, > 95%), sulfur (S, 99.999%), sodium hydroxide (NaOH, 99.99%), sodium iodide (NaI, 99.9%), and iodine (I2, 99.8%) were purchased from Alfa Aesar. Sodium sulfate (Na2SO4, anhydrous, ≥99.0%) was purchased from Sigma−Aldrich. All aforementioned chemicals were used as received. Sodium triiodide (NaI3) electrolyte was prepared by mixing a stoichiometric ratio of NaI and I2 at room temperature (ca. 23 °C). Sodium polysulfide (Na2Sx) electrolytes were prepared by mixing stoichiometric ratios of Na2S and S at room temperature. All electrolytes were prepared using Millipore deionized water (DI water, 18.2 MΩ cm). 2.2. Flow Cell Setup. The flow cell used in this study was similar to previous literature reports with interdigitated flow fields (IDFFs) and a geometric active area of 2.55 cm2.34,35 The backing plates were machined from polypropylene, and the flow fields were machined from 3.18 mm thick impregnated graphite (G347B graphite, MWI, Inc.). Electrodes were cut (16.1 mm × 14.1 mm) from 280 ± 30 μm thick carbon paper (34AA, SGL Group). To improve its hydrophilicity, the as-received carbon paper was first sonicated in isopropyl alcohol (Sigma−Aldrich) and then heated to ca. 45 °C in a solution of concentrated sulfuric and nitric acid (H2SO4 : HNO3 = 3:1 by volume, Sigma− Aldrich). The treated electrodes were then soaked overnight in 1 M NaOH to neutralize the surface acidity. To increase electrochemically active surface area, Vulcan XC72 carbon (VXC72, 250 m2/g surface area, Cabot Corporation) was painted on both the positive and negative electrodes. Cobalt(IV) sulfide particles (CoS2, 200 mesh, 99.5%, Alfa Aesar) were used as an electrocatalyst, and painted on the negative electrode. These pretreatments did not change the electrode thickness. The modified carbon paper electrodes were layered two pieces thick and compressed by ca. 40% in the assembled flow cell, yielding a final total compressed electrode thickness of ca. 330 μm. Nafion membranes with different thicknesses (Ion Power, Inc.) were used as Na+-conductive membranes. To convert Nafion membranes from a protonated form to a sodiated form, the asreceived membranes were consecutively boiled in 3% hydrogen peroxide (Sigma−Aldrich), 0.25 M sulfuric acid, and 0.25 M NaOH for 1 h each. The treated membranes were dried at 120 °C under vacuum for 3 days and rehydrated in DI water overnight before cell assembly. These pretreatments did not change the membrane thickness. Silicone rubber gaskets (McMaster-Carr) sealed the separator and electrodes inside the cell. Capped glass scintillation vials (Wheaton) served as electrolyte reservoirs with holes drilled into the plastic cap to allow tubing in and out. A peristaltic pump (Masterflex L/S Series, Cole-Parmer) was used to drive electrolyte through the flow cell and reservoirs.

Positive: I−3 + 2e− ↔ 3I−

E 0 = 0.54 V vs SHE

Negative: S24 − + 2e− ↔ 2S22 −

E 0 = −0.45 V vs SHE

Overall: 3I− + S24 − ↔ I−3 + 2S22 −

Ecell = 0.99 V

In a recent report, Li et al. proposed a similar flow battery concept based on potassium polyiodide and potassium polysulfide and showed that the chemical costs of the polysulfide/polyiodide electrolytes are lower than that of vanadium electrolytes based on a combination of lower materials costs and higher active species solubility.31 However, their proofof-concept cell performance was at least an order of magnitude lower than state-of-the-art all-vanadium cells.32 While continued improvements are expected through advances in component and B

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the case of iodine, access of undesirable redox couples in the case of sulfur). The positive and negative electrolytes were refreshed every 50 cycles. Specifically, the cycled electrolytes were replaced with fresh electrolytes at 0% SOC, followed by charging the “refreshed” cell to 75% at 20 mA/cm2 and the subsequent longterm cycling. The electrolyte pH before and after cycling was measured using a pH meter (Metrohm).

Norprene tubing (1.6 mm inner diameter, Cole-Parmer) was used to circulate the electrolyte through the system. All flow cell materials were selected in part due to their compatibility with the electrolytes used in this study. 2.3. Flow Cell Testing. All flow cell testing was performed using a Bio-Logic VSP300 potentiostat at room temperature. The electrolyte flow rate was fixed at 10 mL/min throughout all experiments. In the symmetric cell configuration, designated to study the stability of a single electrolyte across a range of state of charge (SOC), sodiated Nafion 117 (Na-N117, 178 μm nominal thickness) was used as the membrane. In the case of the iodine− iodine symmetric cell, the VXC72 loading of the iodine electrode on both sides of the cell was ca. 0.3 mg/cm2. The working electrolyte was 5 mL of 1.5 M NaI + 0.5 M Na2SO4, with a nominal capacity of 134 mAh (at 0% SOC). The counter electrolyte was 15 mL of 0.75 M NaI + 0.25 M NaI3 + 0.5 M Na2SO4 with a nominal capacity of 402 mAh (at 50% SOC). The working electrolyte was first charged (NaI to NaI3) at 20 mA/ cm2 to 75% SOC (capacity cutoff), and then discharged (NaI3 to NaI) at 20 mA/cm2 to −0.5 V (voltage cutoff). In the case of the sulfur−sulfur symmetric cell, the VXC72 and CoS2 loadings of the sulfur electrode on both sides of the cell were both ca. 0.2 mg/cm2 (ca. 0.4 mg/cm2 total). The working electrolyte was 5 mL of 1 M Na2S2 + 1 M NaOH with a nominal capacity of 134 mAh (at 0% SOC). The counter electrolyte was 15 mL of 0.5 M Na2S2 + 0.25 M Na2S4 + 1 M NaOH with a nominal capacity of 402 mAh (at 50% SOC). The working electrolyte was first charged (Na2S2 to Na2S4) at 20 mA/cm2 to 75% SOC (capacity cutoff), and then discharged (Na2S4 to Na2S2) at 20 mA/cm2 to 0% SOC (capacity cutoff). The cell ohmic resistance was measured by impedance before galvanostatic cycling. In the full cell configuration, designated to study the polarization behavior, sodiated Nafion 212 (Na-N212, 51 μm nominal thickness) was used as the membrane. The VXC72 loading of the iodine electrode was ca. 0.3 mg/cm2; the VXC72 and CoS2 loadings of the sulfur electrode were both ca. 0.2 mg/cm2 (ca. 0.4 mg/cm2 total). The positive electrolyte was comprised of 5 mL of 0.75 M NaI + 0.25 M NaI3 + 0.5 M Na2SO4; the negative electrolyte was comprised of 5 mL of 0.5 M Na2S2 + 0.25 M Na2S4 + 1 M NaOH. These electrolytes represent a 1 M electron equivalent concentration with a total theoretical charge storage capacity of 268 mAh and a 50% SOC for the full cell. Galvanostatic polarization was performed to determine the power performance and the polarization behavior for both charge and discharge processes of the cell. The cell voltage stabilized in ca. 10 seconds (s) and the current was held for 30 s to minimize any shift in cell SOC over the course of the experiment. In the full cell configuration, designated to study the long-term cycling performance, Na-N117 was used as the membrane. The VXC72 loading of the iodine electrode was ca. 0.7 mg/cm2; the VXC72 and CoS2 loadings of the sulfur electrode were both ca. 0.5 mg/cm2 (ca. 1.0 mg/cm2 total). The positive electrolyte was comprised of 5 mL 1.5 M NaI + 0.5 M Na2SO4; the negative electrolyte was comprised of 5 mL 0.5 M Na2S4 + 1 M NaOH. These electrolytes represent a 0% SOC for the full cell. The cell was precharged to 75% SOC (nominal) at 20 mA/cm2, which required 2.01 h to complete. The long-term galvanostatic cycling experiments were performed at a constant current density of 20 mA/cm2 for 1.34 h in the charge half cycle, which was equivalent to a 50% SOC swing and with a 0.4 V voltage cutoff in the discharge half cycle. The SOC range was selected to demonstrate cycling behavior without approaching performance limitations associated with extreme SOCs (e.g., mass transport limitations in

3. RESULTS AND DISCUSSION 3.1. Cell Performance. Cell performance was evaluated using a 2.55 cm2 flow cell that leverages the advanced cell architectures described in the state-of-the-art VRFB literature, namely, a zero-gap IDFF and thin hydrophilic carbon-paper electrodes.36,37 The IDFF required that all electrolyte flows through a short path of porous electrode, enabling high current density without developing an unacceptably large pressure drop. Thin carbon-paper electrodes offered a balance of high surface area, good mass transport, and low ohmic resistance. The surface area of both electrodes was increased through the addition of Vulcan carbon. Also, since the kinetics of polysulfide redox reactions are known to be slow on carbon surfaces, CoS2 powder was dispersed on the negative electrode to catalyze the Sn2− (n = 2 or 4) redox reactions.21 To better understand the reversibility of the polyiodide and polysulfide redox processes in the flow cell, we first performed symmetric cell cycling using the same active species on both sides of the cell with a Na-N117 membrane. This approach is similar to traditional bulk electrolysis techniques but allows for a more controlled electrochemical environment by removing the need for a counter electrode of dissimilar material and eliminating the possibility of working electrode contamination by side products generated from reactions at the counter electrode. Furthermore, the flowing electrolyte improves mass transfer, enabling higherconcentration studies and the porous carbon electrodes are more relevant to flow battery applications than the typical reticulated vitreous carbon meshes. In this study, it was necessary to ensure that the full working electrolyte capacity was accessible without having to apply high cell voltages, which could lead to data convolution through activation of additional redox events (e.g., higher-order polysulfides), irreversible side reactions (e.g., water splitting), or reactant electromigration. Thus, we employed a counter electrolyte volume (15 mL) that was 3-fold greater than the working electrolyte volume (5 mL). Cells were cycled at 20 mA/cm2 with a 75% capacity cutoff, based on the working electrolyte. Figure 1a shows representative charge/discharge curves for the I−/I3− couple with low overpotentials, indicating facile redox kinetics17,28 and near-symmetric profiles, indicating a chemically reversible process. This reversibility could also be qualitatively observed by the change of electrolyte from colorless (NaI) to dark reddish brown (NaI3) during charge (oxidation reaction), and vice versa during discharge (reduction reaction). At ca. 20 mAh during discharge (red curve), a minor stepwise decrease of the overpotential is observed, which we tentatively attribute to the dissolution of precipitated NaI3 though further study is needed to confirm this. Indeed, while NaI solubility as high as 7.8 M has been observed in DI water, the NaI3 solubility is significantly lower (5000 cycles) and calendar life (>10 years) required for economical grid storage.10 To fulfill this promise, future research efforts should focus on preventing the decay and/or the crossover of active species, especially the polysulfide electrolytes, and on developing approaches to recycle or regenerate the spent electrolytes. 3.2. Techno-economic Analysis. To estimate the system price, we adopted the techno-economic framework developed by Darling et al.7 combined with selected cell performance metrics described in the previous section. The energy cost includes the chemical cost (NaI, Na2SO4, Na2S4, and NaOH), tank cost, discharge VE, round-trip CE, and SOC range. The reactor cost includes the cell ASR, cell component costs, OCV, and discharge VE. In addition to the energy and power costs, the system price also includes the balance-of-plant and additional costs. The balance-of-plant cost includes heating and cooling equipment, SOC management, power electronics, and pumps, while the additional cost includes manufacturing cost, administration cost, R&D cost, and profit margin.7 Detailed calculations for the techno-economic analysis in Figure 4 are provided in the Supporting Information. We note that the model does not F

DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research in the flow cell cycling, to 6 M, bounded by the solubility of Na2S2 at 25 °C, decreases the energy cost, the extent of which is also more dramatic at lower SOC swings. Increasing the NaI concentration and SOC swing of SIFB may be achievable by, for example, increasing the operating temperature of the cell. Even at the demonstrated concentrations and SOC swing (see the yellow star in Figure 4a), along with their present cost, the overall energy cost of SIFB is lower than not only the present energy cost but also the future energy cost of VRFB. Given the uncertainty of NaI cost, we performed a sensitivity analysis as shown in Figure S3 in the Supporting Information, where the energy cost increases linearly with NaI cost with a slope of 23.84 $/kWh per $/kg for the SIFB demonstrated in this work. Figure 4b compares the system price (the summation of energy cost, power cost, balance-of-plant cost, and additional cost) of VRFB and SIFB. The upper and lower boundaries of both RFB systems reflect the present and future scenarios, respectively. At present, the high price of the SIFB results primarily from an ASR of ca. 4 Ω cm2 (Figure 2a) in this proof-ofconcept flow cell, which is significantly greater than that of stateof-the-art VRFBs using Nafion 212. At this point, charge-transfer resistance on the negative (sulfur) electrode represents the main source of resistance in the cell (ca. 80% of total cell ASR, data not shown). However, this contribution can be significantly reduced via more effective deployment of the catalyst(s) on the negative electrode as prior art indicates that resistance as low as 0.2 Ω cm2 are achievable.23 In addition, lower ohmic resistance (hardware + electrolytes + membrane) is possible through further cell-level optimization (e.g., use of thinner membranes). Based on these potential reductions in charge transfer and ohmic resistances (see details in the Supporting Information), a total cell ASR of 0.74 ohm cm2 can be optimistically projected. If realized, this, along with the decreased cell component costs, would reduce the power cost to $60/kW from the present $1860/kW. Along with its competitive energy cost, SIFB has the ability to outperform VRFB in terms of future cost at all energy/power (E/P) ranges, and shows the potential to meet the $100/kWh price target with E/P between 6 and 10 h (purple band in Figure 4b), which is the storage duration of particular interest for a RFB system. Within this E/P range, Figures 4c and 4d show the sensitivity of the overall system price to changes in energy and power cost, respectively. For all discharge durations, a decrease of energy cost or power cost leads to a decrease of the system price. Furthermore, the impact of power cost on the system price reduction is more dramatic than that of energy cost, which suggests that future research efforts should focus on decreasing the power cost, primarily via improved membranes with high conductivity and selectivity as well as active electrocatalysts to accelerate the polysulfide redox reactions on the negative side of the battery.

cycles at 20 mA/cm2 with a duration of ca. 530 h. The crossover of the polysulfide species was identified as a key performancelimiting factor that results in both inefficiency and capacity decay. The results from these cell studies were used to inform a systemlevel techno-economic model, which predicts the present and future state system prices for this conceptual battery and compares the results to VRFBs and established targets. Technoeconomic analysis revealed that energy cost is more sensitive to the concentration of actives at low cell SOC swing and, provided that reasonable concentrations (1 M e−) and SOC swings (50%) are achieved as is the case here, the system price is more sensitive to the power cost than to the energy cost. Furthermore, reduction in power costs via improved reactor performance and in energy costs via an increase in the concentration of actives, can lead to a battery that meets the $100/kWh price target within the desired E/P range. Realizing the promise of this flow battery system will require overcoming several technical challenges. First, highly conductive and selective cation exchange membranes are necessary to achieve the low ASR (high power) and low active species crossover (high capacity retention). Membrane selectivity remains a challenge for all RFBs that employ two different species for charge storage. This favors single-component systems, such as the VRFB, where species crossover reduces CE but does not lead to irreversible capacity fade. Second, despite the high solubility of NaI, the lower solubility of NaI3 limits the achievable energy density (and, thus, energy costs). Increases in NaI3 solubility may be achieved by increasing temperature or incorporating solubilized agents (e.g., ethanol17). Third, this study demonstrated the redox reactions between S22− and S42−, which account for only 25% of sulfur’s theoretical capacity (1675 mAh/g). Enabling deeper reduction to S2− at practical concentrations, without sacrificing reversibility, would significantly increase the energy density of the SIFB.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.iecr.7b01476.

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4. CONCLUSIONS AND PERSPECTIVE Herein, we explored the feasibility of a sodium polysulfide− polyiodide RFB for achieving the low system prices necessary for grid energy storage. To this end, we performed cell-level studies on a proof-of-concept prototype to investigate individual electrolyte and full cell performance characteristics. The symmetric cell experiments showed good redox reversibility of both the sulfide- and iodide-based electrolytes between 0 and 75% SOC. The discharge peak power of polysulfide-polyiodide with nominal 1 M [e−] and at 50% SOC was determined to be 65 mW/cm2 with a total cell ASR of 4.0 Ω cm2 during discharge. The galvanostatic cycling of SIFB was demonstrated for 200

Details of the experimental description and the technoeconomic analysis (PDF)

AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Fikile R. Brushett: 0000-0002-7361-6637 Present Address §

Department of Chemistry, Nankai University, Tianjin, China.

Notes

The authors declare no competing financial interest. G

DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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student in Professor Brushett’s group from 2016 to 2017. His research focused on the investigation of the electrochemical and solution properties of aqueous sulfur electrolytes. He will pursue a Ph.D. degree in the Department of Chemistry at Tsinghua University.

Liang Su obtained his Ph.D. degree from the Department of Chemical & Biomolecular Engineering at the University of Connecticut in 2013. He subsequently joined Professor Brushett’s research group in the Department of Chemical Engineering at the Massachusetts Institute of Technology (MIT) as a postdoctoral associate. His research focuses on the development and system-level analysis of cost-effective aqueous redox flow batteries for large-scale energy storage.

Jesse Hinricher is pursuing a bachelor’s degree in the Department of Chemical Engineering at the Massachusetts Institute of Technology. He is interested in electrochemical processes for energy storage and has worked on silicon solar technology. His current research focuses on the development of diagnostic techniques to characterize redox electrolyte performance in flow batteries.

Andres Badel obtained his B.S. degree from the Department of Chemical Engineering at MIT in 2017. He started his research in Professor Brushett’s group in the summer of 2014. His work focused on the electrochemical characterization of aqueous organic and sulfur-based redox flow batteries. He will pursue a Ph.D. degree in the Department of Materials Science and Engineering at MIT.

Fikile Brushett is an Assistant Professor of Chemical Engineering at MIT, where he holds the Raymond A. (1921) and Helen E. St. Laurent Career Development Chair. He received his B.S.E. in Chemical & Biomolecular Engineering from the University of Pennsylvania in 2006 and his Ph.D. in Chemical Engineering from the University of Illinois at Urbana−Champaign in 2010. From 2010 to 2012, he was a Director’s Postdoctoral Fellow in the Electrochemical Energy Storage group at Argonne National Laboratory. In 2013, he began his independent career at MIT, where his research group advances the science and engineering of electrochemical technologies needed for a sustainable energy economy. He also serves as the Lead Grid Technologist for the Joint Center for Energy Storage Research, a U.S. Department of Energy-funded Energy Innovation Hub.

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ACKNOWLEDGMENTS This work was supported as part of the Joint Center for Energy Storage Research (JCESR), an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science, Basic Energy Sciences. A.F.B. gratefully acknowledges the SuperUROP program at MIT for financial support. We also thank Menghsuan

Changsu Cao received his B.S. degree in Chemistry from Nankai University in 2017. He worked as a visiting undergraduate H

DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

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Industrial & Engineering Chemistry Research

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Pan and Prof. Yet-Ming Chiang from the Department of Materials Science and Engineering at MIT for stimulating discussions. Finally, we appreciate the valuable feedback from members of the Brushett Group at MIT throughout the project. This invited contribution is part of the I&EC Research special issue for the 2017 Class of Influential Researchers.

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DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX

Article

Industrial & Engineering Chemistry Research Crossover of Lithiated Nafion 117 in Nonaqueous Electrolytes. J. Electrochem. Soc. 2016, 163 (1), A5253. (40) Darling, R.; Gallagher, K.; Xie, W.; Su, L.; Brushett, F. Transport Property Requirements for Flow Battery Separators. J. Electrochem. Soc. 2016, 163 (1), A5029.

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DOI: 10.1021/acs.iecr.7b01476 Ind. Eng. Chem. Res. XXXX, XXX, XXX−XXX