FUNDAMENTAL FLOW BATTERY STUDIES: ELECTRODES AND ELECTROLYTES By MALLORY A. MILLER Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy Dissertation Advisor: Dr. Robert F. Savinell Department of Chemical and Biomolecular Engineering CASE WESTERN RESERVE UNIVERSITY May, 2017 CASE WESTERN RESERVE UNIVERSITY DISSERTATION APPROVAL We hereby approve the thesis/dissertation of ___________________Mallory A. Miller___________________ Candidate for the Doctor of Philosophy degree* _______________Professor Robert Savinell_______________ _______________Professor Jesse Wainright_______________ ________________Professor Burcu Gurkan________________ ________________Professor Mark DeGuire________________ Date _____December 13, 2016_____ *We also certify that written approval has been obtained for any proprietary material contained therein. II Dedication To my mother for always believing in me and for her encouragement and support. III Table of Contents Acknowledgements .................................................................................................................. VIII List of Tables ............................................................................................................................... IX List of Figures ............................................................................................................................ XII Abbreviations ........................................................................................................................ XXIV Abstract .................................................................................................................................. XXVI Chapter 1. Introduction and Background .................................................................................. 1 1.1 Redox Flow Batteries .............................................................................................................. 1 1.2 Specific Motivations and Scope ............................................................................................. 5 1.2.1 Ionic Liquids - A Different Approach to Non-Aqueous ..................................................... 5 1.2.2 Electrode Kinetics ............................................................................................................. 7 1.3 Concluding Remarks .............................................................................................................. 9 1.4 Publications ........................................................................................................................... 10 Chapter 2. Prospect of Ionic Liquids as Redox Flow Battery Electrolytes .......................... 12 2.1 Introduction and Literature................................................................................................. 12 2.1.1 Ionic Liquids .................................................................................................................... 12 2.1.1.i Ionic Liquids for Electrochemical Applications ....................................................... 16 2.1.1.ii Ionic Liquids for Flow Batteries .............................................................................. 18 2.1.1.iii Iron Electrochemistry - an Introduction ................................................................. 21 2.1.1.iv Physical Properties of Deep Eutectic Solvents (DES) ............................................ 22 IV 2.2 Iron-Containing Ionic Liquid Electrolytes ......................................................................... 25 2.2.1 Iron Electrokinetics ......................................................................................................... 27 2.2.2 Electrodeposition of Iron................................................................................................. 30 2.2.2.i Nucleation Mechanism ............................................................................................. 31 2.2.3 Physical Properties of the Electrolytes ........................................................................... 40 2.2.3.i Effect of Chloride to Iron Ratio on Conductivity ...................................................... 40 2.2.3.ii Walden Plot ............................................................................................................. 42 2.2.4 Iron Speciation ................................................................................................................ 44 2.2.4.i X-ray Absorption Near Edge Structure Measurements ............................................ 44 2.2.4.ii X-ray Photoelectron Spectroscopy .......................................................................... 47 2.2.4.iii Raman Spectroscopy .............................................................................................. 51 2.3 Iron IL Flow Battery - Proof of Concept ............................................................................ 54 2.4 Conclusions ............................................................................................................................ 56 Chapter 3. Technique Development, Carbon Fiber Microelectrodes ................................... 58 3.1 Introduction and Literature................................................................................................. 58 3.2 Technique Development - Carbon Fiber Microelectrode ................................................. 61 3.2.1 Preconditioning ............................................................................................................... 62 3.2.2 Electrochemically Active Area ........................................................................................ 65 3.3 Potential Applications ........................................................................................................... 67 3.3.1 Non-Aqueous Systems - Understanding Kinetics and Degradation ................................ 67 3.3.2 Metal Electrodeposition for Hybrid RFBs ...................................................................... 72 V 3.4 Conclusions ............................................................................................................................ 75 Chapter 4. Carbon Electrode Pretreatment Effects ............................................................... 77 4.1 Introduction and Literature................................................................................................. 77 4.2 Carbon Electrode Treatments ............................................................................................. 78 4.3 Surface Analysis Results ...................................................................................................... 79 4.3.1 Scanning Electron Microscopy ....................................................................................... 80 4.3.2 Electrochemical Capacitance.......................................................................................... 81 4.3.3 XPS Analysis.................................................................................................................... 82 4.3.5 Contact Angle Characterization ...................................................................................... 87 4.4 Applications to the All-Vanadium System - Carbon Fiber Electrodes for Understanding of Electrokinetics ......................................................................................................................... 89 4.4.1 Significant Results ........................................................................................................... 90 4.4.1.i Kinetic Parameters from EIS and LSV ..................................................................... 92 4.4.1.ii Effects of Treatment Potential ................................................................................. 94 4.4.1.iii Development of a Mechanistic Model .................................................................... 98 4.5 Concluding Remarks .......................................................................................................... 106 Chapter 5. Conclusions and Future Work ............................................................................ 108 5.1 Conclusions .......................................................................................................................... 108 5.1.1 Ionic Liquids as RFB Electrolytes ................................................................................. 108 5.1.2 The CFME, Technique Development ............................................................................ 109 5.1.3 Carbon Electrode Pretreatment Effects ........................................................................ 110 VI 5.2 Future Work ........................................................................................................................ 111 5.2.1 Other Halides and Hydrogen Bond Donors .................................................................. 111 5.2.2 Investigation of Alternative Active Metal Species ......................................................... 111 5.2.3 Aqueous All-iron Flow Battery with Choline Chloride Supporting Electrolyte (and Choline as an Additive for Plating) ............................................................................................ 112 5.2.4 Ionic Liquids for High Power Energy Storage Applications (Supercapacitors)........... 112 Appendix A1. Halides and Hydrogen Bond Donors .............................................................. 114 A1.1 Introduction .....................................................................................................................