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UC Riverside UC Riverside Electronic Theses and Dissertations Title Electrospun Nanofibers for Applications in Energy Harvesting and Generation Permalink https://escholarship.org/uc/item/01h168g7 Author Yu, Sooyoun Publication Date 2020 Peer reviewed|Thesis/dissertation eScholarship.org Powered by the California Digital Library University of California UNIVERSITY OF CALIFORNIA RIVERSIDE Electrospun Nanofibers for Applications in Energy Harvesting and Generation A Dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Chemical and Environmental Engineering by Sooyoun Yu September 2020 Dissertation Committee: Dr. Nosang Vincent Myung, Chairperson Dr. Juchen Guo Dr. Ian Wheeldon Copyright by Sooyoun Yu 2020 The Dissertation of Sooyoun Yu is approved: Committee Chairperson University of California, Riverside AKNOWLEDGEMENTS I would like to dedicate this great honor to a handful of people. First and foremost, I give my greatest gratitude to my principal investigator, Professor Nosang Vincent Myung. He has been my rock, my teacher, my mentor, my friend. Throughout these years, he has been one of the most consistent aspects of my life, during which I had my fair share of struggles and stressful days. My five years at UC Riverside would not have been so fruitful and nothing short of a blessing had it not been for his guidance and support. He truly lives up to his “nickname” of my academic father. I am so grateful to have him on my side and excited that I still have more to learn from him. Secondly, my family. My parents, who live in South Korea, have more than made up for the physical distance that keeps us apart; their unconditional love, support, and faith in me, their countless prayers, advice, virtual hugs and kisses I received made me more confident in myself. My “American parents”, Minah and Youngho. All of the memories we shared over the years not only helped me through some difficult times, but also will be some of my most cherished memories of my life in California. My beloved husband, Riki, who has always been there for me, through thick and thin, long or short straw – you showed me time and again I can and should be proud of myself. I love you and would not trade you for anything in the world – not even if I were to get a freebie Ph.D. And finally, Yuri – the pure bundle of joy who decided to come to me and Riki during what seemed like the darkest time of 2020. You kept me company and helped me in ways that you didn’t even know, and your father and I cannot wait to greet you into the world. iv Last, but of course not least, all of my friends and colleagues who have cheered me on, supported me in their own unique ways, parted their wisdom, shared their struggles, lifted me up and pushed me forward. I thank all of you. Of course, my work would not have been possible without: • Previously published works Yu, S. & Myung, N. V. Minimizing the Diameter of Electrospun Polyacrylonitrile (PAN) Nanofibers by Design of Experiments for Electrochemical Application. Electroanalysis 30, (2018) Chen, Q., Yu, S., Myung, N. & Chen, W. DNA-guided assembly of a five- component enzyme cascade for enhanced conversion of cellulose to gluconic acid and H2O2. J. Biotechnol. 263, 30–35 (2017) • Funding from National Science Foundation (Award number 1263818) • Access to the field-emission scanning electron microscope (ThermoFisher Scientific NNS450) granted by the Central Facility for Advanced Microscopy and Microanalysis at University of California, Riverside v ABSTRACT OF THE DISSERTATION Electrospun Nanofibers for Applications in Energy Harvesting and Generation by Sooyoun Yu Doctor of Philosophy, Chemical and Environmental Engineering University of California, Riverside, September 2020 Dr. Nosang Vincent Myung, Chairperson Electrospun nanofibers have gained great research interest for decades as attractive nanomaterial for various applications due to their ultra-high specific surface area, flexibility in materials, and ease of fabrication. Furthermore, fine tuning of electrospinning or post-electrospinning process conditions can allow for precise control of morphology, composition, physical, electrical, and electrochemical properties to tailor the nanofibers for a specific application. In this work, the effect of various electrospinning-related conditions on properties of polyacrylonitrile (PAN)-derived nanofibers was elucidated by series of systematic variation of parameters called design of experiment (DOE). Analyses on the DOE revealed solution viscosity, mainly controlled by polymer concentration, was the predominant factor for nanofiber morphology, while the addition of composite materials such as multi-walled carbon nanotubes and zinc acetate also strongly affected the nanofiber dimensions. vi To study the suitability of the PAN nanofibers with controlled properties for applications in energy harvesting and generation, piezoelectric and electrochemical properties of PAN-derived as-spun and heat-treated nanofibers were characterized. For the first time, size-dependent piezoelectric properties for PAN nanofibers was carefully investigated, which showed the voltage generated perpendicular to the direction of the fiber (V33) increased as a function of decreasing fiber dimensions, similar to more commonly studied piezoelectric polymers. Electroanalytical methods such as cyclic voltammetry, linear polarization and electrochemical impedance spectroscopy were employed to investigate the feasibility of various carbonaceous nanofibers as electrode material. Enzymatic fuel cell was chosen as the device of interest for energy generation application in this work. In an attempt to utilize the naturally abundant yet complex cellulose as fuel, a multienzyme cascade complex in nature called cellulosome was biomimetically fabricated by site-specific immobilization of 5 enzymes on customized DNA scaffold for sequential hydrolysis of cellulose followed by catalytic oxidation of glucose for electricity generation. With successful demonstration of the synergistic effect of enzyme immobilization on DNA scaffold, similar system was functionalized onto an electrode for preliminary electrochemical studies, which exhibited great promise as multienzyme cascade-based bioanode for cellulolytic fuel cell. vii TABLE OF CONTENTS Chapter 1: Recent Advances in the Direct Electron Transfer-Enabled Enzymatic Fuel Cells.............................................................................................................................1 1.1 Abstract ......................................................................................................................1 1.2 Introduction ................................................................................................................1 1.3 Biocatalyst engineering ..............................................................................................4 1.3.1 Mutated enzymes .................................................................................................4 1.3.2 Orientation of enzymes........................................................................................8 1.4 Biocatalyst immobilization methods ........................................................................10 1.4.1 Physisorption .....................................................................................................12 1.4.2 Entrapment and conducting polymers ...............................................................13 1.4.3 DNA as scaffolds or electron acceptors ...........................................................15 1.5 Nanomaterial-based electrodes.................................................................................17 1.5.1 Carbonaceous materials ....................................................................................17 1.5.2 Porous nanostructure ........................................................................................18 1.5.3 Gold nanoparticles ............................................................................................20 1.6 Recent progress in biomedical application of DET-enabled EFC ..........................22 1.7 Conclusions and outlook .........................................................................................25 1.8 References ...............................................................................................................26 Chapter 2: Electrospun Polyacrylonitrile-Derived Nanofibers and Their Controlled Physical, Piezoelectric, and Electrochemical Properties via Design of Experiment ..38 2.1 Abstract ....................................................................................................................38 2.2 Introduction ..............................................................................................................39 2.2.1 Electrospun nanofibers ......................................................................................39 2.2.2 Piezoelectric energy harvesting .........................................................................43 2.2.3 Nanofibers for fuel cells ....................................................................................53 2.3 Materials and Methods .............................................................................................55 2.4 Results and Discussion .............................................................................................63 2.4.1 PAN nanofibers .................................................................................................63