University of Connecticut OpenCommons@UConn Doctoral Dissertations University of Connecticut Graduate School 5-4-2018 Water and Anion Transport in Electrochemical Devices Travis Omasta University of Connecticut - Storrs, [email protected] Follow this and additional works at: https://opencommons.uconn.edu/dissertations Recommended Citation Omasta, Travis, "Water and Anion Transport in Electrochemical Devices" (2018). Doctoral Dissertations. 1808. https://opencommons.uconn.edu/dissertations/1808 Water and Anion Transport in Electrochemical Devices Travis John Omasta, Ph.D. University of Connecticut, 2018 In this thesis, the balance and transport of water, hydroxide, and carbonates in Anion Exchange Membrane Fuel Cells (AEMFCs) are investigated. First, macro-scale water is examined, and the need for high membrane conductivity, a predictor of water back diffusion, is demonstrated by operating at lower relative humidities to avoid catalyst layer flooding. Additionally, the distribution of water in the membrane, electrodes, and gas diffusion layers was directly imaged with neutron radiography in an operando fuel cell. The insight from the neutron images was combined with electrode diagnostics evaluating the kinetic, ohmic, and mass transport limitations of the cell, resulting in the ability to also control the micro- scale water through precise engineering of the anode catalyst layer. This understanding ultimately led to the ability reduce the Pt loading significantly, as well as use non-Pt catalysts, while still achieving > 1 W cm-2. Finally, the effects of CO2 and carbonation on AEMFCs was investigated, and the mechanism for carbonate inclusion in the AEM and removal are discussed. It was observed that the carbonation/decarbonation dynamics could allow for the purposeful use of carbonates in electrochemical devices, including current driven electrochemical CO2 separation, which were assembled and their performance characterized. Water and Anion Transport in Electrochemical Devices Travis John Omasta B.S., University of Connecticut, 2006 M.S., University of Connecticut, 2017 A Dissertation Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy at the University of Connecticut 2018 APPROVAL PAGE Doctor of Philosophy Dissertation Water and Anion Transport in Electrochemical Devices Presented by Travis John Omasta, B.S., M.S. Major Advisor ___________________________________________________________________ William E. Mustain Associate Advisor ___________________________________________________________________ Radenka Maric Associate Advisor ___________________________________________________________________ Jeffrey McCutcheon Associate Advisor ___________________________________________________________________ Ugur Pasaogullari Associate Advisor ___________________________________________________________________ Yu Lei University of Connecticut 2018 ii ACKNOWLEDGMENTS The number of people that I am indebted to for support and guidance through my journey to earn my PhD is significant, and without them this achievement would not have been possible. First, I must express my most sincere appreciation to my advisor. Dr. William Mustain, who’s guidance through my early failures and ultimate successes helped to shape the scientist I am today. More than expertise in electrochemistry, Bill guided me to hone the problem-solving approach that defines a Ph.D. researcher, and I honestly could not have asked for a better balance of strict motivation and friendly understanding through all the difficulties inherent to earning a Ph.D. in Chemical Engineering. Also vital to my success, was my family, for their unwavering support and understanding through the most stressful times, which happened often over the 5+ years I was back in school. It was not easy to return to UConn after graduating 6 years prior, and my parents, sisters, bother-in-laws, and nieces and nephews always knew how to bring a smile to my face when I needed it most, and I can’t wait to spend more time with them after graduation. A heartfelt thank you to Pete Menard and Garry Barnes for their technical expertise in setting up equipment and experiments, and for helping keep me sane by always making me laugh with random jokes/wisecracks. I would also like to thank Mark Drobney at Tech Services for always being willing to work with me in whatever crazy design I was trying to accomplish, including the wilds task of building a plexiglass submersible for a demo to use in my fluid dynamics class. Additionally, I owe Carol Stork, at the University of South Carolina significant iii gratitude, without her knowledge of all things USC and Swearingen, I would never have been able to pull off the renovation of the Mustain lab at USC and overcome the “southern pace” of South Carolina. I am also extremely grateful for the many collaborators that I have worked closely with during my graduate career, especially Dr. Bryan Pivovar, Dr. John Varcoe, Dr. Jacob LaManna, and Dr. Michael Zuraw; and my associate advisors: Dr. Brian Willis, Dr. Ugur Pasaogullari, Dr. Jeffrey McCutcheon, Dr. Yu Lei, and Dr. Radenka Maric, all of whom have contributed to my knowledge and growth. I would like to acknowledge my lab mates: Neil Spinner, Greg Crettol, Sujan Shrestha, Ying Liu, Shuai Zhao, Derek Chhiv, Mengchen Liu, Ehsan Faegh, Ben Ng, Xinyi Zhao, Yiwei Zheng and Emanuele Magliocca for their collaboration and friendship. I would like to especially thank Connor Lewis, who and contributed invaluably to my experiments, as an undergrad researcher, and as a friend. I also owe significant appreciation to Xiong Peng, who was side by side with me through a large portion of the journey, and many of our best ideas came from going back and forth on a multitude of topics. Finally, I can’t say enough about Alex Palmieri, my lab mate, my friend, and my part time roommate. Especially in the move to South Carolina, his friendship was invaluable and simpatico. Lastly, I would like to thank all my friends, new and old, from Danbury, UConn undergrad, and developed during my graduate studies at UConn – through ChEGSA, softball, and classes – for their support, visits, and mostly for the distractions from the stress of the program. Be it a visit to UConn, a brewery, a ski trip, a softball game, a beer, a run, lunch or a Dunkin run, it was always appreciated. iv Dedicated to the memory of my nephew Nathan William Lounsbury (2012-2013). May his brief time with us be a constant reminder to cherish the time we have and strive to be the best versions of ourselves. v TABLE OF CONTENTS ACKNOWLEDGMENTS..................................................................................... iii LIST OF TABLES ............................................................................................... xi LIST OF FIGURES ............................................................................................. xii CHAPTER 1: Introduction ................................................................................. 1 1.1. Significance ..................................................................................................... 1 1.2. Background ..................................................................................................... 5 1.2.1. Historical Context for Alkaline Fuel Cells ........................................................... 5 1.2.2. Carbonation Limitations for AFCs and AEMFCs ................................................. 9 1.2.3. Competition with Acidic Fuel Cells ................................................................... 15 1.3. The Properties of AEMs and Their Influence on Water Transport in AEMFCs.... 19 1.3.1. Role of Physical Properties in Determining Membrane and Water Behavior.. 19 1.3.2. Understanding the Water Content and Balance in AEMFCs ........................... 20 1.3.3. AEMFC Performance with Conductivity, Back Diffusion, and Water Control .. 23 1.4. AEMFC Catalyst and Electrode Improvements and Limitations ........................ 28 1.4.1. The Impact of Electrode Design on AEMFC Water .......................................... 28 1.4.2. Reducing PGM and Eliminating Pt in the AEMFC Electrode ............................ 30 1.5. Emergence and Impacts of Carbonate Anions in AEMFCs ................................ 31 1.5.1. Carbonate Influences on Cell Operation .......................................................... 31 1.5.2. Electrochemical Carbonate Removal ............................................................... 34 vi 1.5.3. Possible Purposeful Utilization of Carbonates in AEM-based Systems ............ 35 1.6. Successes with “Commercial” AEMFC Systems ............................................... 38 CHAPTER 2: Importance of Balancing Membrane and Electrode Water in Anion Exchange Membrane Fuel Cells ..................................................................... 41 2.1. Experimental ................................................................................................. 42 2.1.1. AEM Synthesis and Characterization ............................................................... 42 2.1.2. Anion-Exchange Ionomer (AEI) Powder Synthesis ........................................... 44 2.1.3. Materials and Gas Diffusion Electrode (GDE) Preparation .............................. 47 2.1.4. MEA Assembly and Single-Cell AEMFC Testing ............................................... 48 2.2. Results and Discussion ................................................................................... 51 2.2.1. Cell