Non-Aqueous Single-Metal Redox Flow Batteries by Aaron A. Shinkle A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Chemical Engineering) in the University of Michigan 2013 Doctoral Committee: Assistant Professor Charles W. Monroe, Co-Chair Professor Levi T. Thompson Jr., Co-Chair Professor John W. Halloran Associate Professor Suljo Linic 1 Acknowledgements I would like to acknowledge the support of the dissertation committee, Monroe research group, Thompson research group, Prof. Rasmussen, and Dr. Sleightholme. I would like to thank the University of Michigan-Fraunhofer Alternative Energy Technologies for Transportation program for funding my research. The Electron Microbeam Analysis Laboratory and Horace Rackham Graduate School were also instrumental in the completion of research for my degree. ii Table of Contents Acknowledgements ............................................................................................... ii List of Figures ....................................................................................................... vi List of Tables ..................................................................................................... xvii List of Abbreviations ......................................................................................... xviii Abstract ............................................................................................................... xx Chapter 1 Introduction .......................................................................................... 1 1.1 Introduction to Redox Flow Batteries ....................................................... 1 1.2 Aqueous Redox Flow Battery Systems ................................................... 4 1.3 Non-aqueous Systems .......................................................................... 10 Chapter 2 Effects of the Liquid Electrolyte .......................................................... 18 2.1 Experimental Techniques ...................................................................... 18 2.1.1 Cyclic Voltammetry ......................................................................... 18 2.1.2 Charge/Discharge ........................................................................... 24 2.2 Active-Species Metal Center ................................................................. 37 2.2.1 Background and Approach ............................................................. 37 2.2.2 Results: Manganese Acetylacetonate ............................................. 38 2.2.3 Results: Chromium Acetylacetonate ............................................... 44 2.2.4 Results: Vanadium Acetylacetonate ............................................... 50 2.2.5 Discussion ...................................................................................... 58 2.3 Ligand Modification................................................................................ 60 2.3.1 Background ..................................................................................... 60 2.3.2 Approach ........................................................................................ 62 2.3.3 Results ............................................................................................ 64 2.3.4 Discussion & Future Ligand Work ................................................... 78 2.4 Solvent and Support Selection .............................................................. 79 iii 2.4.1 Background ..................................................................................... 79 2.4.2 Experimental Design ....................................................................... 81 2.4.3 Results: Physical Properties ........................................................... 85 2.4.4 Results: Electrochemical Properties ............................................... 90 2.4.5 Discussion: Desired Solution Properties ......................................... 97 2.4.6 Conclusion .................................................................................... 106 Chapter 3 Effects of the Cell Components ....................................................... 108 3.1 Membrane ........................................................................................... 108 3.1.1 Background ................................................................................... 108 3.1.2 Results: Pretreatment ................................................................... 112 3.1.3 Results: Impedance ...................................................................... 118 3.1.4 Discussion & Future Membrane Work .......................................... 122 3.2 Electrodes ........................................................................................... 124 3.2.1 Background ................................................................................... 124 3.2.2 Approach ...................................................................................... 126 3.2.3 Results: Experimental ................................................................... 127 3.2.4 Results: Mechanistically-Based Kinetic Model .............................. 130 3.2.5 Discussion .................................................................................... 144 Chapter 4 Redox Flow Battery Performance .................................................... 146 4.1 Degradation Mechanisms .................................................................... 146 4.1.1 Approach ...................................................................................... 146 4.1.2 Results: Cyclic Voltammetry ......................................................... 147 4.1.3 Results: Charge/Discharge − Modest Oxygen Content Glovebox 154 4.1.4 Results: Charge/Discharge – Minimal Oxygen Content Glovebox 159 4.1.5 Discussion .................................................................................... 161 4.1.6 Summary ...................................................................................... 163 4.2 Concentration tests.............................................................................. 164 4.2.1 Background and Approach ........................................................... 164 4.2.2 Results .......................................................................................... 167 4.2.3 Discussion .................................................................................... 175 4.3 Capacity .............................................................................................. 177 iv 4.3.1 Background and Approach ........................................................... 177 4.3.2 Results: Electrochemistry ............................................................. 177 4.3.3 Results: Scanning Electron Microscopy ........................................ 188 4.3.4 Discussion .................................................................................... 197 Chapter 5 Conclusion and Future Work ........................................................... 201 5.1 Conclusion ........................................................................................... 201 5.2 Future Work ......................................................................................... 206 Bibliography ...................................................................................................... 210 v List of Figures Figure 1.1.1-1 General schematic of a redox flow battery .................................... 3 Figure 1.2.1-1 Cyclic voltammogram with a glassy carbon disk electrode in (aqueous) 0.01 M VOSO4 and 2 M H2SO4 in ultrapure H2O. Scan rate 10 mV/s; measurements performed at room temperature. .................................................. 9 Figure 1.3.1-1 Charging profile for 0.1 M ruthenium acetylacetonate and 1 M TEABF4 in acetonitrile at a current of 1 mA. (Reprinted from Chakrabarti et al. [52]) .................................................................................................................... 12 Figure 2.1.1-1 Cyclic voltammetry cell ................................................................ 20 Figure 2.1.1-2 Cyclic voltammogram of 0.1 M tetraethylammonium tetrafluoroborate in acetonitrile. Glassy carbon working electrode. Scan rate 25 mV/s. .................................................................................................................. 23 Figure 2.1.1-3 Cyclic voltammogram of 0.01 M V(acac)3 and 0.1 M tetraethylammonium tetrafluoroborate in acetonitrile. Glassy carbon working electrode. Scan rate 25 mV/s. ........................................................................... 24 Figure 2.1.2-1 Photograph of an H-type charge/discharge cell. The blue liquid represents the volume filled with liquid electrolyte. ............................................. 26 Figure 2.1.2-2 Photograph of the 1-D type charge/discharge cell. The brown liquid is a typical V(acac)3 electrolyte. ................................................................ 26 Figure 2.1.2-3 Chronoamperometry of 0.5 M TEABF4 in acetonitrile. Aluminum electrodes in an H-cell with Neosepta AHA membrane. [Blue (upper line)] Potential input to the cell, [Red (lower line)] Current response. .......................... 28 Figure 2.1.2-4 Cyclic voltammogram of 0.01 M V(acac)3 and 0.05 M TEABF4 in acetonitrile. Scan rate 100 mV/s. Working electrode: aluminum foil, counter electrode: graphite plate, reference electrode: Ag/Ag+. ...................................... 29 vi Figure 2.1.2-5 Chronoamperometry of graphite