Person: Gerhardt, Michael
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Gerhardt
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Gerhardt, Michael
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Publication A metal-free organic–inorganic aqueous flow battery(Nature Publishing Group, 2014) Huskinson, Brian Thomas; Marshak, Michael; Suh, Changwon; Er, Suleyman; Gerhardt, Michael; Galvin, Cooper J.; Chen, Xudong; Aspuru-Guzik, Alan; Gordon, Roy; Aziz, MichaelAs the fraction of electricity generation from intermittent renewable sources—such as solar or wind—grows, the ability to store large amounts of electrical energy is of increasing importance. Solid-electrode batteries maintain discharge at peak power for far too short a time to fully regulate wind or solar power output\(^{1, 2}\). In contrast, flow batteries can independently scale the power (electrode area) and energy (arbitrarily large storage volume) components of the system by maintaining all of the electro-active species in fluid form\(^{3, 4, 5}\). Wide-scale utilization of flow batteries is, however, limited by the abundance and cost of these materials, particularly those using redox-active metals and precious-metal electrocatalysts\(^{6, 7}\). Here we describe a class of energy storage materials that exploits the favourable chemical and electrochemical properties of a family of molecules known as quinones. The example we demonstrate is a metal-free flow battery based on the redox chemistry of 9,10-anthraquinone-2,7-disulphonic acid (AQDS). AQDS undergoes extremely rapid and reversible two-electron two-proton reduction on a glassy carbon electrode in sulphuric acid. An aqueous flow battery with inexpensive carbon electrodes, combining the quinone/hydroquinone couple with the \(Br_2/Br^-\) redox couple, yields a peak galvanic power density exceeding 0.6 W cm^{−2} at 1.3 A cm^{−2}. Cycling of this quinone–bromide flow battery showed >99 per cent storage capacity retention per cycle. The organic anthraquinone species can be synthesized from inexpensive commodity chemicals\(^8\). This organic approach permits tuning of important properties such as the reduction potential and solubility by adding functional groups: for example, we demonstrate that the addition of two hydroxy groups to AQDS increases the open circuit potential of the cell by 11% and we describe a pathway for further increases in cell voltage. The use of π-aromatic redox-active organic molecules instead of redox-active metals represents a new and promising direction for realizing massive electrical energy storage at greatly reduced cost.Publication Dissecting the quinone bromide flow battery(2015) Chen, Qing; Gerhardt, Michael; Eisenach, Louise; Marshak, Michael; Gordon, Roy; Aziz, MichaelPublication Novel Quinone-Based Couples for Flow Batteries(The Electrochemical Society, 2013) Huskinson, Brian Thomas; Nawar, Saraf; Gerhardt, Michael; Aziz, MichaelFlow batteries are of interest for low-cost grid-scale electrical energy storage in the face of rising electricity production from intermittent renewables like wind and solar. We report on investigations of redox couples based on the reversible protonation of small organic molecules called quinones. These molecules can be very inexpensive and may therefore offer a low cost per kWh of electrical energy storage. Furthermore they are known to rapidly undergo oxidation and reduction with high reversibility under some conditions, suggesting the possibility of high current density operation, which could lead to low cost per kW. We report cyclic voltammetry measurements for 1,4-parabenzoquinone in neutral pH aqueous solution using a three-electrode setup. We report full fuel cell measurements as well, utilizing p-benzoquinone in an acidic solution as a positive electrode material and a hydrogen negative electrode, where current densities in excess of 240 mA \(cm^{-2}\) have been achieved to date. These initial results indicate that the quinone/hydroquinone redox couple is a promising candidate for use in redox flow batteries.Publication Quinone electrochemistry in acidic and alkaline solutions and its application in large scale energy storage(2015) Gerhardt, Michael; Lin, Kaixiang; Chen, Qing; Marshak, Michael; Tong, Liuchuan; Gordon, Roy; Aziz, MichaelPublication Alkaline quinone flow battery(American Association for the Advancement of Science (AAAS), 2015) Lin, Kaixiang; Chen, Qing; Gerhardt, Michael; Tong, Liuchuan; Kim, Sang Bok; Eisenach, Louise; Valle, Alvaro; Hardee, D.; Gordon, Roy; Aziz, Michael; Marshak, MichaelStorage of photovoltaic and wind electricity in batteries could solve the mismatch problem between the intermittent supply of these renewable resources and variable demand. Flow batteries permit more economical long-duration discharge than solid-electrode batteries by using liquid electrolytes stored outside of the battery. We report an alkaline flow battery based on redox-active organic molecules that are composed entirely of Earth-abundant elements and are nontoxic, nonflammable, and safe for use in residential and commercial environments. The battery operates efficiently with high power density near room temperature. These results demonstrate the stability and performance of redox-active organic molecules in alkaline flow batteries, potentially enabling cost-effective stationary storage of renewable energy.Publication Comparison of Capacity Retention Rates During Cycling of Quinone-Bromide Flow Batteries(Cambridge University Press (CUP), 2016) Gerhardt, Michael; Beh, Eugene; Tong, Liuchuan; Gordon, Roy; Aziz, MichaelWe use cyclic charge-discharge experiments to evaluate the capacity retention rates of two quinone-bromide flow batteries (QBFBs). These aqueous QBFBs use a negative electrolyte containing either anthraquinone-2,7-disulfonic acid (AQDS) or anthraquinone-2-sulfonic acid (AQS) dissolved in sulfuric acid, and a positive electrolyte containing bromine and hydrobromic acid. We find that the AQS cell exhibits a significantly lower capacity retention rate than the AQDS cell. The observed AQS capacity fade is corroborated by NMR evidence that suggests the formation of hydroxylated products in the electrolyte in place of AQS. We further cycle the AQDS cell and observe a capacity fade rate extrapolating to 30% loss of active species after 5000 cycles. After about 180 cycles, bromine crossover leads to sufficient electrolyte imbalance to accelerate the capacity fade rate, indicating that the actual realization of long cycle life will require bromine rebalancing or a membrane less permeable than Nafion® to molecular bromine.Publication Cycling of a Quinone-Bromide Flow Battery for Large-Scale Electrochemical Energy Storage(The Electrochemical Society, 2014) Huskinson, Brian Thomas; Marshak, Michael; Gerhardt, Michael; Aziz, MichaelWe have demonstrated the performance of an aqueous redox flow battery composed of a negative electrode consisting of a redox couple between anthraquinone di-sulfonate and its corresponding hydroquinone, and a positive electrode consisting of a redox couple between hydrobromic acid and bromine. The peak power density is approximately 0.6 W/cm2. After 750 deep cycles, the average discharge capacity retention is 99.84% per cycle and the average current efficiency is 98.35%.Publication Dissection of the Voltage Losses of an Acidic Quinone Redox Flow BatteryChen, Qing; Gerhardt, Michael; Aziz, MichaelWe measure the polarization characteristics of a quinone-bromide redox flow battery with interdigitated flow fields, using electro- chemical impedance spectroscopy and voltammetry of a full cell and of a half cell against a reference electrode. We find linear polarization behavior at 50% state of charge all the way to the short-circuit current density of 2.5 A/cm2. We uniquely identify the polarization area-specific resistance (ASR) of each electrode, the membrane ASR to ionic current, and the electronic contact ASR. We use voltage probes to deduce the electronic current density through each sheet of carbon paper in the quinone-bearing electrode. By interpreting the results using the Newman 1-D porous electrode model, we deduce the volumetric exchange current density of the porous electrode. We uniquely evaluate the power dissipation and identify a correspondence to the contributions to the electrode ASR from the faradaic, electronic, and ionic transport processes. We find that, within the electrode, more power is dissipated in the faradaic process than in the electronic and ionic conduction processes combined, despite the observed linear polarization behavior. We examine the sensitivity of the ASR to the values of the model parameters. The greatest performance improvement is anticipated from increasing the volumetric exchange current density.