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Spatiotemporal Mapping of Electrochemical Diffusion Layers Spatiotemporal Mapping of Electrochemical Diffusion Layers A Thesis Submitted to the College of Graduate Studies and Research In Partial Fulfillment of the Requirements For the Degree of Masters of Science In the Department of Chemistry University of Saskatchewan, Saskatoon By: Michael James Lardner Copyright © Michael J. Lardner, June, 2016. All rights reserved PERMISSION TO USE In presenting this thesis in partial fulfillment of the requirements for a Postgraduate degree from the University of Saskatchewan, I agree that the Libraries of this University may make it freely available for inspection. I further agree that permission for copying of this thesis in any manner, in whole or in part, for scholarly purposes may be granted by the professor or professors who supervised my thesis work or, in their absence, by the Head of the Department or the Dean of the College in which my thesis was completed. It is understood that any copying or publication or use of this thesis or parts thereof for financial gain shall not be allowed without my written permission. It is also understood that due recognition shall be given to me and to the University of Saskatchewan for any scholarly use of any material in my thesis. Requests for permission to copy or to make other use of material in this thesis in whole or in part should be addressed to: Head of the Department of Chemistry University of Saskatchewan Saskatoon, Saskatchewan S7N 5C9 Canada i Abstract Although pure electrochemical techniques can provide substantial knowledge about electrochemical reaction mechanisms, they lack the ability to provide direct molecular structure information about the species involved. This inability to extract molecular information can result in mechanistic ambiguity with respect to the identity of the reaction intermediates. This information can be obtained by coupling in situ spectroscopic methodologies with electrochemical techniques. This is known as spectroelectrochemistry. A particularly problematic area of study with spectroelectrochemical techniques is the analysis of the mass transport of species within the diffusion layer of the electrode. The visualization of the diffusion layer surrounding electrodes allows for the unambiguous determination of electrode processes. However, a high degree of spatial and temporal resolution is needed as the diffusion layer in a typical electrochemical reaction extends to a thickness of hundreds of microns in tens of seconds. While traditional infrared spectroelectrochemical techniques have been valuable for the study of electrochemical processes, they do not provide the spatial and/or the temporal resolution that is needed to examine the diffusion layers produced at electrodes. This thesis focuses on the development of an IR technique that couples synchrotron based IR radiation (SIR) with electrochemistry, allowing for the concentrations of species present within the diffusion layer of an electrode to be mapped during an electrochemical reaction. The reduction of ferricyanide and oxidation of hydroquinone (HQ) are used as test redox systems to study the ability of SIR to map electrochemical diffusion layers. The resulting diffusion coefficients of ferricyanide, ferrocyanide, hydroquinone and benzoquinone are extracted using the IR method developed here and compared to those determined independently by hydrodynamic linear sweep voltammetry (HLSV). The diffusion coefficients of all species as determined by SIR diffusion layer mapping will be shown to be consistent with the diffusion coefficients determined by HLSV. This validates the ability of SIR diffusion layer mapping to monitor electrochemically generated diffusion layers. ii Acknowledgements I would like to thank Dr. Ian Burgess for all of his help, support, guidance and patience and for making my graduate studies an enjoyable experience. Without him, I would have not been exposed to the wonderful world of spectroelectrochemistry, known the joy of running experiments at the Canadian Light Source, nor would the thesis you are about read have been possible. I would like to thank the other members of the Burgess Empire and its associated members for making every day in the Burgess lab amazing. A huge thanks to Ted Toporowski, Blair Chomyshen and Jill Cornish of the Physics Machine Shop at the University of Saskatchewan who turned my designs into reality. Without their skillz none of this work would have been possible. This project would also not be possible without all the support, guidance and suggestions of the Mid-IR beamline scientists, Dr. Ferenc Borondic, Tim May, Dr. Xia Liu and Dr. Scott Rosendahl. Shout out to Dr. Ferenc Borondic for shooting down my first cell design within 5 seconds of seeing it. Thanks to Dr. Vicki Meli for all her help and support and for suggesting that I pursue graduate studies in the Burgess Group. I would also like to thank my parents who have given me their love and support every step of the way. I am blessed have you two, your advice and encouragement has been of an unimaginable help throughout these last couple of years. I promise one day you’ll understand what I do. Finally I need to thank my fiancé Emily who came across Canada to join me on this adventure. Having you here has been a blessing. I don’t think I would have been able to get through this without you. iii Table of Contents PERMISSION TO USE ............................................................................................................................... i Abstract ........................................................................................................................................................ ii Acknowledgements .................................................................................................................................... iii List of Figures ............................................................................................................................................ vii List of Tables .............................................................................................................................................. xi List of Abbreviations ................................................................................................................................ xii Chapter 1: Introduction ............................................................................................................................. 1 1.1: Spectroelectrochemistry .................................................................................................................. 1 1.2: IR Spectroelectrochemistry ............................................................................................................ 2 1.3: Diffusion ........................................................................................................................................... 4 1.4: Thesis Goals...................................................................................................................................... 7 1.5: Scope of the Thesis ........................................................................................................................... 8 1.6: References....................................................................................................................................... 11 Chapter 2: Literature Review .................................................................................................................. 13 2.1: Introduction ................................................................................................................................... 13 2.2: Scanning Electrochemical Microscopy ........................................................................................ 13 2.3: UV-Vis............................................................................................................................................. 19 2.4: Raman ............................................................................................................................................. 22 2.5: Fluorescence ................................................................................................................................... 24 2.7: IR ..................................................................................................................................................... 30 2.8: References....................................................................................................................................... 32 Chapter 3: Techniques and Theory ......................................................................................................... 36 3.1: Cyclic Voltammetry ....................................................................................................................... 36 3.2: Hydrodynamic Linear Sweep Voltammetry ............................................................................... 36 3.3: Chronoamperometry ..................................................................................................................... 38 3.4 Infrared Spectroscopy .................................................................................................................... 39 3.4.1: Infrared Radiation .................................................................................................... 39 3.4.2: Michelson Interferometer ......................................................................................... 41 3.4.3: Infrared Microscopy ................................................................................................
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