Two extremely stable anthraquinone negolytes were synthesized from inexpensive precursors that potentially decrease the mass production cost. The carbon-linked anthraquinones eliminate S N 2 or S N Ar side reactions. Pairing with a Fe(CN) 6 3À/4À posolyte, they exhibited an open-circuit voltage of 1.0 V. By operating at pH 14, a record low capacity fade rate of <1% per year was demonstrated.

hybrid RFBs electrodeposit at least one active species, e.g., lithium, aluminum, or zinc, onto nonflowing electrodes. The metal deposition process usually occurs on the negative electrode side. Although many hybrid RFBs utilize nonaqueous electrolytes to attain high working potential, a zinc-based hybrid system can attain a relatively high working potential in a nonflammable, lower-cost aqueous electrolyte. This is because the zinc/zincate redox couple, Zn/[Zn(OH) 4 ] 2− , in a pH 14 alkaline solution has the advantage of a large negative redox potential of −1.23 V versus the standard hydrogen electrode (SHE). An example is the alkaline zincferricyanide hybrid RFB, which was first reported in the 1970s and is still under development. [3] However, the low solubility of the [Fe(CN) 6 ] 3− /[Fe(CN) 6 ] 4− couple at high pH limits the energy density and constrains practical implementation. [4] In addition, acidic zinc-bromine hybrid RFBs have been widely studied and are being commercialized; however, the toxicity and corrosivity of bromine limits widespread deployment. [1] Recently, redox-active organic and organometallic molecules have been widely studied for their promise of enabling the development of inexpensive flow batteries. [5][6][7] These molecules exhibit structural diversity and broad tunability, permitting the engineering of solubility, redox potential, kinetics, and stability. Many different types of molecules, including quinones, [8][9][10][11][12] phenazines, [13,14] viologens, [7,[15][16][17][18][19] alloxazines, [20] and (2,2,6,6-tetramethylpiperidin-1-yl)oxidanyl, [13,15,16,21,22] have demonstrated good electrochemical performance as redox-active materials in aqueous organic redox flow batteries (AORFBs). Most of these molecules exhibit low reduction potentials and consequently have been explored as negolyte (negative electrolyte) materials. Some exceptions are tetrachloro-1,4 benzoquinone and 4,5-dihydroxybenzene-1,3-disulfonic acid, which have high positive reduction potentials of >0.8 V versus SHE in acidic solution. [9,11,23] Thus, by pairing high potential organic molecules such as these with the Zn/[Zn(OH) 4 ] 2− redox couple, a new type of hybrid RFB can be designed to achieve a high cell voltage.However, it is difficult to pair an alkaline electrolyte and an acidic electrolyte within conventional single-membrane RFBs due to H + or OH − crossover. Recently, ceramic membranes and bipolar polymer membranes have been introduced into singlemembrane pH-differential flow cells, but the high resistance of these membranes has severely limited the current density. [24,25] Water-soluble redox-active organic molecules have attracted extensive attention as electrical energy storage alternatives to redox-active metals that are low in abundance and high in cost. Here an aqueous zinc-organic hybrid redox flow battery (RFB) is reported with a positive electrolyte comprising a functionalized 1,4-hydroquinone bearing four (dimethylamino)methyl groups dissolved in sulfuric acid. By utilizing a three-electrolyte...

Changing the reactor design paradigm for improved CO2 electrolyzers through advanced manufacturing.

We demonstrate the effect of varying the channel and land width dimensions of an interdigitated flow field experimentally and through computational modeling. Measured polarization curves (overpotential versus current density) are reported for a symmetric cell with a ferrocyanide-ferricyanide electrolyte in aqueous potassium chloride. A two-dimensional, coupled fluid dynamic and electrochemical model is developed to interpret polarization results from the symmetric cell. This model suggests that stagnant fluid zones above the center lines of the interdigitated channels negatively impact cell performance. A three-dimensional computational fluid dynamic model is used to calculate the pressure drop and power losses associated with flowing fluid through these flow fields. The voltage efficiency of the cell, corrected for pumping power losses, is evaluated and reported as a function of channel and land width to identify high-efficiency flow fields. The implications for the engineering of large-area flow fields are discussed.

Quinone-based aqueous flow batteries provide a potential opportunity for large-scale, low-cost energy storage due to their composition from earth abundant elements, high aqueous solubility, reversible redox kinetics and their chemical tunability such as reduction potential. In an operating flow battery utilizing 9,10-anthraquinone-2,7-disulfonic acid, the aggregation of an oxidized quinone and a reduced hydroquinone to form a quinhydrone dimer causes significant variations from ideal solution behavior and of optical absorption from the Beer-Lambert law. We utilize in situ UV-Vis spectrophotometry to establish (a), quinone, hydroquinone and quinhydrone molar attenuation profiles and (b), an equilibrium constant for formation of the quinhydrone dimer (K) ∼ 80 M. We use the molar optical attenuation profiles to identify the total molecular concentration and state of charge at arbitrary mixtures of quinone and hydroquinone. We report density functional theory calculations to support the quinhydrone UV-Vis measurements and to provide insight into the dimerization conformations. We instrument a quinone-bromine flow battery with a Pd-H reference electrode in order to demonstrate how complexation in both the negative (quinone) and positive (bromine) electrolytes directly impacts measured half-cell and full-cell voltages. This work shows how accounting for electrolyte complexation improves the accuracy of electrochemical modeling of flow battery electrolytes.

We present a method for comparing porous electrodes for use in redox flow batteries. By comparing physical and electrochemical properties of six carbon cloth electrodes (CCEs) including hydraulic permeability, Ohmic resistance, and mass transport overpotential, we show how optimal engineering conditions such as compression and electrolyte flow rates can be derived. These results are combined and applied to a quinone-based redox flow battery, leading to a peak power density around 0.4 W cm −2 for several different CCEs. This method can be applied broadly to other electrode architectures and flow battery chemistries, and provides a comprehensive framework for their comparison.

We demonstrate the electrochemical oxidation of an anthracene derivative to a redox-active anthraquinone at room temperature in a flow cell without the use of hazardous oxidants or noble metal catalysts....

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