June 16 th, Charles Monroe, Levi Thompson, Alice Sleightholme, and Aaron Shinkle University of Michigan Department of Chemical Engineering

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1 Non Aqueous Vanadium Redox Flow Batteries June 16 th, 2010 Charles Monroe, Levi Thompson, Alice Sleightholme, and Aaron Shinkle University of Michigan Department of Chemical Engineering Christian Doetsch, Sascha Berthold, Birgit Brosowski Fraunhofer Institute UMSICHT Jens Tuebke, Jens Noack Fraunhofer Institute ICT

2 Project Outline 1/2 Framework: Cooperation between University of Michigan (United States) and Fraunhofer Gesellschaft (Germany) established Project Partners: University of Michigan: Department of Chemical Engineering (Prof. Levi Thompson, Prof. Charles Monroe) Fraunhofer Institute UMSICHT and ICT (Dr. Christian Doetsch, Dr. Jens Tuebke) Project Aim: Examination, developing and testing of materials and stack design for a non aqueous redox flow battery

3 Project Outline 2/2 Main advantages of non aqueous systems: Higher Voltage level No Hydrogen/oxygen production Higher energy densitiy Work plan: Redox Chemistry, materials, membranes: University of Michigan Prototype development: Fraunhofer ICT Scale up, test bench: Fraunhofer UMSICHT Time Frame: Start End of 2009 / Duration 24 months

4 Single metal Redox Flow Batteries Aqueous all vanadium redox flow battery (RFB) Performance depends on Half cell potentials (power density) Active species concentration (energy density) Electrolyte reservoir volume (charge capacity)

Commercial Redox Flow Battery Chemistry Existing RFBs mostly use aqueous electrolytes: Iron/chromium Bromine/polysulfide Zinc/bromine All vanadium ZBB Energy Corp, 500kWh

5 Commercial Redox Flow Battery Chemistry Existing RFBs mostly use aqueous electrolytes: Iron/chromium Bromine/polysulfide Zinc/bromine All vanadium ZBB Energy Corp, 500kWh Zn Br RFB Multi metal chemistries susceptible to crossover Cell potential limited by water electrolysis (E = 1.23 V) Non aqueous electrolytes enable higher cell potentials

6 Non Aqueous Vanadium RFB Electrodes Source Separator Catholyte Tank Anolyte Tank V (IV) e V(III) V(II) V(III) e Vanadium Acetylacetonate Tester et al. The MIT Press ; Single metal RFB mitigates cross contamination Energy density dependent on: Cell potential Electrolyte concentration Electrolyte reservoir volume

7 Equation of the solvent Current density/ma cm V II /V III 1.4V V IV /V V Current density/ma cm V II /V III 2.2V V III /V IV Aqueous Potential/V vs. SHE 0.01 M VOSO 4 (active species) [vanadyl sulfat] 2 M H 2 SO 4 /ultrapure H 2 O (support) Glassy carbon working electrode Non aqueous Potential/V vs.she 0.01 M V(acac) 3 (active species) [vanadium actetylacetonate] 0.1 M TEABF 4 /CH 3 CN (support) [Tetra ethyl ammonium tetrafluoroborate] Glassy carbon working electrode

8 Progress: Redox Chemistry a) Current density/ma cm mv/s 300 K Current density/ma cm mv/s 300 K Potential/V vs. SHE Peak circled in red corresponds to oxidation of V(acac) 3 to VO(acac) 2 produced from active species in presence of air Potential/V vs. Ag/Ag + Presence of Cl ions (from membrane manufacturing) produces extra peak close to VIII/VIV redox couple

9 Linear Sweep Voltammetry (LSV) Current normalized by limiting current Diffusion Coefficient 1 D = 1.8 x 10 5 ± 3.5 x 10 6 cm 2 /s Composition: 0.01M V(III) (acac) M TEABF 4 in CH 3 CN Quasi reversible Model Butler Volmer 1 Small reductant concentration Microelectrode (Steady State) i i f i (1 ) f i o 1 i L, c e 1 e i o (Exchange current density) and φ (Standard Potential) are fit parameters (1) Bard and Faulkner. Electrochemical Methods. 2001

10 Linear Sweep Voltammetry: V(III) / V(IV) Redox Couple Carbon Scan rate: 1 mv/s Gold Scan rate: 0.5 mv/s i o = 3 A/m 2 i o = 170 A/m 2

11 Linear Sweep Voltammetry: V(III) / V(IV) Redox Couple Platinum Scan rate: 0.5 mv/s All i o = 90 A/m 2

12 Progress: Membrane diagnostics Implementation of proposed one dimensional test cell Critical system variables: liquid solutions membranes (or MEA) electrode materials (or endcaps)

13 Progress: Membrane diagnostics Charge/discharge with anion exchange membrane (Neosepta AHA) underway Au electrodes, flow by mode, 0.1 M V(acac) 3 [vanadium actetylacetonate] and 0.5 M TEABF 4 /CH 3 CN [Tetra ethyl ammonium tetrafluoroborate / Acetonitrile] Voltage/V Current/mA Voltage/V Time/hours Time/hours Charge current 0.4 ma, discharge 0.05 ma; Burn in complete after 3 cycles 85% Coulombic efficiency

14 Progress: Prototype development task Redox Flow Test Cell First Results 10 cm² active area Graphite felt (COS1006) Bipolar plate (Schunk GmbH, Germany) Microporous membrane (Scimat) 0.1 M V(Acac) M TEABF 4 Acetonitrile Impedance spectroscopy R ct = 1590 C = 1.02 mf R s = 5

15 Progress: Prototype development task Redox Flow Test Cell Charge / Discharge 0,03 0, ,5 2,0 0,02 0,05 0,04 40 Voltage [V] 1,5 1,0 0,5 0,01 0,00-0,01 Current [A] Power [W] 0,03 0,02 0,01 0, Charge [Ah] 0,0 Voltage Current Time [h] -0,02-0, Time [h] 0 20 ma (2 ma/cm²) galvanostatic charge up to 2 V, 2.2 V, 2.4 V, 2.6 V 5 min OCV Measurement 5 ma (0.5 ma/cm²) galvanostatic discharge down to 0.3 V Voltage [V] Pout [mw/cm²] CE 80 % 66 % 64 % EE 24 % 23 % 22 %

16 Progress: Scale up Cell / Stack Design cell data (for a liquid, aqueous system) number of cells 2 membrane area 1600 cm² Voltage (charge) 3,3 V (2 x 1.65 V) Current A Currently testing materials, sealings, glue for non aqueous system

17 Scale up and test bench Design and erecting a first test facility as a mobile test bench 15 kw power Electrolyte tank: 2 x 40 l 2kWh Stack size up to 1 x 0.8 x 0.3 m 200 kg Charge 0 40 V A Discharge < 40 V A Flow rate l/min

Allen J. Bard, Netzahualcóyotl Arroyo-Currás (Netz Arroyo), Jinho Chang, Brent Bennett. Department of Chemistry and Center for Electrochemistry

REDOX Allen J. Bard, Netzahualcóyotl Arroyo-Currás (Netz Arroyo), Jinho Chang, Brent Bennett Department of Chemistry and Center for Electrochemistry The University of Texas at Austin 1 What is a redox