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1 123 Journal of Solid StateElectrochemistryCurrent Research and Development inScience and Technology ISSN 1432-8488 J Solid State ElectrochemDOI cycle based on a high specific energyaqueous flow battery and its potential usefor fully electric vehicles and for directsolar-to-chemical energy conversionYuriy V. Tolmachev, Andrii Piatkivskyi,Victor V. Ryzhov, Dmitry V. Konev &Mikhail A. Vorotyntsev123 Your article is protected by copyright andall rights are held exclusively by Springer-Verlag Berlin Heidelberg. This e-offprint isfor personal use only and shall not be self-archived in electronic repositories. If you wishto self-archive your article, please use theaccepted manuscript version for posting onyour own website. You may further depositthe accepted manuscript version in anyrepository, provided it is only made publiclyavailable 12 months after official publicationor later and provided acknowledgement isgiven to the original source of publicationand a link is inserted to the published articleon Springer's website.

2 The link must beaccompanied by the following text: "The finalpublication is available at .FEATURE ARTICLEE nergy cycle based on a high specific energy aqueous flow batteryand its potential use for fully electric vehicles and for directsolar-to-chemical energy conversionYuriy V. Tolmachev&Andrii Piatkivskyi&Victor V. Ryzhov&Dmitry V. Konev&Mikhail A. VorotyntsevReceived: 20 January 2015 /Revised: 16 February 2015 /Accepted: 19 February 2015#Springer-Verlag Berlin Heidelberg 2015 AbstractAflowbatteryemployingH2as the fuel and one ormore of highly soluble halate salts (such as 50 %w/wLiBrO3aq.) as the oxidant presents a viable opportunity as a powersource for fully electric vehicles which meets the specific en-ergy, specific power, energy efficiency, cost, safety, and refilltime requirements.

3 We further disclose a process of regenera-tion of the fuel and the oxidant from the discharged halide saltand water using electric (or solar) energy as the only input andgenerating no chemical waste. The cycle of discharge and re-generation takes advantage of pH-driven comproportionationand disproportionation reactions, respectively, and of pH ma-nipulation using an orthogonal ion migration across laminarflow (OIMALF ) unusual features in the electroreduction of anions origi-nating from electric double layer effects attracted much atten-tion of Frumkin and his associates long time ago [1 3]who engaged M. A. Vorotyntsev into developing the corre-sponding theoretical foundations of ion transport [4]. Decadeslater, another question about a different peculiarity specific tothe electroreduction of halogen oxoanions was raised by Tolmachev in relation to the cathodic discharge process inhigh specific energy regenerative flow batteries utilizing high-ly soluble aqueous multi-electron oxidants (AMOs ), suchas chlorates and bromates of lithium, magnesium, and calcium[5 7].

4 Fortuitously, the paths of Tolmachev and Vorotyntsevcrossed around that time [8], resulting in their joint work onthe development of theoretical models underlying theelectroreduction of AMOs [9].Flow batteries ( , middle) are more similar to fuel cells( , top) than to batteries with solid electroactive materials(SEAM) ( , bottom) since the former also use fluid (gas,liquid, or dissolved in liquids) reagents. In fuel cells, the fluid fuel (hydrogen, methanol, borohydride solution, etc.) is oxidizedat the negative electrode, while the oxygen reduction reactiontakes place at the positive electrode. Fuel cells are notrecharged electrically but rather refilled mechanically by sup-plying the oxidant (usually, O2from air) and the fuel (whichcreates the sustainability problem, , where to get the fuelfrom).

5 In redox flow batteries, the oxidant is not air but ratherit is present in the oxidant fluid supplied to the positive elec-trode. Also, in contrast to fuel cells, redox flow batteries can beelectrically recharged by reversing the direction of the currentthat flows through the battery during discharge. Another advan-tage of flow batteries compared to low-temperature fuel cells isa possibility of the elimination (or of a significant reduction ofThis article is dedicated to Prof. Vorotyntsev on the occasion of V. Tolmachev (*)Ftorion, Inc., Boston, MA 02120, USAe-mail: Piatkivskyi:V. V. RyzhovNorthern Illinois University, DeKalb, IL 60115, USAD. V. Konev:M. A. VorotyntsevInstitute for Problems of Chemical Physics, Chernogolovka, RussiaD. V. Konev:M. A. VorotyntsevMendeleev University of Chemical Technology of Russia,Moscow, RussiaM.)

6 A. VorotyntsevLomonosov Moscow State University, Moscow, RussiaM. A. VorotyntsevICMUB UMR 6302 CNRS, Universite de Bourgogne, Dijon, FranceJSolidStateElectrochemDOI 's personal copythe amount) of expensive platinoid electrocatalyst(s) since theslow electroreduction of O2is replaced by a more reversibleelectrochemical process. Conventional redox flow batteries(such as all-vanadium, iron-chromium) have low power densi-ties (typically, < W/cm2)[10 18] which results in the cost ofpower being too high for stationary energy storage. The recentsurge of interest in hydrogen bromine flow batteries, [19]forwhich an areal power of W cm2has been demonstrated[20], gives hopes that flow batteries may finally find acceptancein stationary energy storage. However, the low energy density(heavy weight) and the corrosive electrolytes used in all com-mercialized flow batteries prevent their use in fully electricvehicles (FEVs), despite the conveniences of a quick refill time,of decoupling of energy and power scales, and of off-boardregeneration afforded by the flow AMO oxidants present several important advan-tages over the oxidants used in flow batteries previously.

7 First,both the AMOs and their reduction products (halides ofthese cations) have enormous solubilities in water [21 31](for example, bromate and bromide of lithium at 20 C pro-duce saturated aqueous solutions of M M concentrations, respectively) which, whencoupled with the six-electron electroreduction process, leadsto very high energy densities unbefitting flow batteries here-tofore. More specifically, as disclosed in Ftorion s patentapplications [5 7], these highly soluble multi-electron saltshave charge content, over 1000 Ah/kg of solution. Second,the autocatalytically accelerated electroreduction (1) (2)ofhalogen oxoanions may deliver very large discharge currents(over 3 A/cm2) and a very high areal power (over 2 W/cm2)even when low-cost electrode materials such as carbon are used[9].

8 Additional benefits of AMO flow batteries comprise the useof cheap electrode materials ( , carbonaceous), abundant (seebelow), inexpensive, safe and environmentally benign reagents,as well as the anionic nature of the oxidant (halate) and of thefinal product of its reduction (halide) which prevents their cross-over to the negative electrode when durable and commerciallyavailable cation-selective membranes (such as Nafion ) the cathode3Br2 6e 6Br ; 1 In the catholyte6H Br BrO3 3H2O 3Br2 2 On the anode3H2 6e 6H 3 During discharge, the reduction of one or more AMOs on the negative electrode is combined with anodic process (3),such as the oxidation of H2,NaBH4, etc., with a cation trans-port across the separating membrane. The use of the H2 AMO combination is especially interesting since it opensthe prospect of full recycling of all reagents in stoichiometricamounts without irreversible consumption of any chemicalsand without generating any waste (see below) [5 7].

9 Suchenergy cycle is particularly attractive for FEVs because theregeneration process (see below) can be performed either on-board by plugging the electric vehicle to the grid or off-boardin a stationary regeneration system followed by a mechanicaltransfer of hydrogen and oxidant fluid to the storage tanksonboard of a several interesting highly soluble AMOs shownin , we selected lithium bromate for our initial studiessince bromine/bromide electrochemistry is quite reversibleeven on carbonaceous electrodes [20,32 37] and since, in thisinitial work, we wanted to avoid potential problems with theformation of poorly soluble hydroxides of, for example, Mg2+and Ca2+, during regeneration. In what follows, hydrogen ox-idation process was employed on the negative electrode inexperiments with complete bromic acid used in this work was synthesized accordingto refs.

10 [39,40]. Lithium bromate was prepared according torefs. [21,22]. In both cases, Ba(BrO3)2( % pure fromAmerican Elements) was used as the bromate source, andFig. 1 Schematic comparison of a hydrogen PEM fuel cell (top), ahydrogen bromine flow battery (middle), and a SEAM (lithium ion)battery (bottom). Positive electroactive materials are colored inred,negative inblue, inert electron conductive materials are inblack,andion conducting polymers are inyellowJ Solid State ElectrochemAuthor's personal copyH2SO4or Li2SO4were used to precipitate Ba2+. The LiBrO3solution produced thereby was processed using a rotary evap-orator to obtain a dry solid rotating disk electrode (RDE) setup, including apotentiostat and a mm diameter glassy carbon RDE, wasprocured from Pine Instruments.