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Investigation of Asymmetric Hybrid Supercapacitor Based on Morphology of Zinc Oxide Electrode Materials for High Energy Supercapacitors

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Investigation of Asymmetric Hybrid Supercapacitor Based on Morphology of Zinc Oxide Electrode Materials for High Energy Supercapacitors INVESTIGATION OF ASYMMETRIC HYBRID SUPERCAPACITOR BASED ON MORPHOLOGY OF ZINC OXIDE ELECTRODE MATERIALS FOR HIGH ENERGY SUPERCAPACITORS by SUMAIYAH NAJIB A thesis submitted to Faculty of Engineering for Natural Sciences and Engineering in partial fulfillment of the requirements for the degree of Master of Science SABANCI UNIVERSITY AUGUST, 2020 i i © Sumaiyah Najib 2020 All Rights Reserved i ABSTRACT INVESTIGATION OF ASYMMETIC HYBRID SUPERCAPACITOR BASED ON MORPHOLOGY OF ZINC OXIDE ELECTRODE MATERIALS FOR HIGH ENERGY SUPERCAPACITORS Sumaiyah Najib Supervisor: Assoc.Prof.Dr. Emre Erdem Keywords: nanomorphology, asymmetric hybrid supercapacitors, point defect, EPR spectroscopy Supercapacitors are highly attractive for large number of emerging mobile devices for energy storage and harvesting issues. In this thesis, we present a summary of the recent developments in supercapacitor research and technology, including all kinds of supercapacitor design techniques using various electrode materials and production methods. It also covers the current progress achieved in novel materials for supercapacitor electrodes. The latest produced EDLC, Hybrid, Pseudo supercapacitors have also been described. Metal oxides, specifically ZnO, used as electrode materials with different morphologies are in focus here. The ZnO nanostructures were synthesized in the form of nanoparticles, nanoflowers and nanourchins. Structural, electronic and optical characterization of the samples were done via standard techniques such as XRD, SEM, Photoluminescence, Raman and UV-Vis spectroscopy. The point defect structures which are specific to each morphology has been investigated in terms of their concentration and location via state of art EPR spectroscopy. According to core-shell model the samples all revealed core defects however the defects on the surface smeared out. Finally, all three morphology has been tested as electrode material in a real supercapacitor device and the performance of the device, particularly the specific capacitance and the storage mechanism has been mediated by the point defects. Morphology dependent defective ZnO electrode enable to monitor the working principle of supercapacitor device from EDLC to pseudosupercapacitor. ii ÖZET YÜKSEK ENERJI SÜPERKAPASITÖRLERI IÇIN ÇINKO OKSIT ELEKTROT MALZEMELERININ MORFOLOJISINE DAYALI ASIMETRIK HIBRID SÜPER KAPASITÖRLERIN ARAŞTIRILMASI Sumaiyah Najib Danışman: Assoc.Prof.Dr. Emre Erdem Anahtar Kelimeler: nanomorfoloji, asimetrik hibrit süperkapasitörler, nokta kusur, EPR spektroskopisi Süper kapasitörler, enerji depolama ve hasat sorunları için çok sayıda yeni ortaya çıkan mobil cihaz için oldukça caziptir. Bu tezde, çeşitli elektrot malzemeleri ve üretim yöntemleri kullanarak her türlü süperkapasitör tasarım teknikleri dahil olmak üzere süperkapasitör araştırma ve teknolojisindeki son gelişmelerin bir özetini sunuyoruz. Aynı zamanda, süperkapasitör elektrotları için yeni materyallerde elde edilen mevcut ilerlemeyi de kapsamaktadır. En son üretilen EDLC, Hybrid, Pseudosüperkapasitörler de burada açıklanmıştır. Farklı morfolojilere sahip elektrot malzemeleri olarak kullanılan metal oksitler, özellikle ZnO, burada odaklanmaktadır. ZnO nanoyapıları, nanopartiküller, nanoflowerler ve nanourchinler şeklinde sentezlendi. Numunelerin yapısal, elektronik ve optik karakterizasyonu XRD, SEM, fotolüminesans, Raman ve UV-Vis spektroskopisi gibi standart tekniklerle yapılmıştır. Her bir morfolojiye özgü nokta kusur yapıları, konsantrasyonları ve konumları açısından EPR spektroskopisi ile araştırılmıştır. Core-shell modeline göre, numunelerin tümü çekirdek kusurlarını ortaya çıkarmış, ancak yüzeydeki kusurlar lekelenmiştir. Son olarak, üç morfolojinin tamamı, gerçek bir süper kapasitör cihazında elektrot malzemesi olarak test edilmiştir ve cihazın performansı, özellikle spesifik kapasitans ve depolama mekanizması, nokta kusurları tarafından aracılık edilmiştir. Morfolojiye bağlı kusurlu ZnO elektrodu, EDLC’den psödosüperkapasitörlere kadar süperkapasitör cihazının çalışma prensibinin izlenmesini sağlar. iii Acknowledgement It has been an absolute privilege for me to embark on this journey. I am thankful to Almighty God for this opportunity. It has opened me up to a whole new world beyond my imagination. More so to raise my values and work ethic, in addition to opening doors for future pursuits and pathways. I am deeply grateful to my supervisor, Assoc. Prof. Dr. Emre Erdem for being a guide and giving me the freedom to learn and grow at my own pace and leading me all through out when I needed direction. Also, I am indebted to our collaborators who have generously contributed towards my journey in the past two years from SUNUM, TOBB Ankara, and in Università di Catania, Italy. Finally, I am thankful to my family and friends without whom none of this would have been possible. iv Table of Contents LIST OF FIGURES vii LIST OF TABLES viii LIST OF ABBREVIATION ix 1. INTRODUCTION 1 2. CLASSIFICATION OF SUPERCAPACITORS 4 2.1 Electrochemical Double Layer Capacitors (EDLC) 4 2.1.1 Carbon Aerogels, Carbon Foams and Carbid-derived Carbon (CDC) 6 2.1.2 Graphene and Carbon Nanotubes (CNT) 6 2.1.3 Activated Carbon (AC) 8 2.2 Pseudocapacitors 8 2.2.1 Conducting Polymer Pseudocapacitors 9 2.2.2 Metal Oxide Pseudocapacitors 9 2.3 Hybrid Supercapacitors 10 2.3.1 Asymmetric Hybrid Supercapacitors 11 2.3.2 Composite Hybrid Supercapacitor (CHS) 11 2.3.3 Rechargeable Battery-type Hybrid Supercapacitors 12 3. SUPERCAPACITOR DEVICE DESIGN 14 3.1 Sample Synthesis 17 ZnO Crystal and Sample Nanostructures 17 Nanoparticles (NP) and Nanourchins (NU) 19 Nanoflowers (NF) 20 3.2 Methods 22 4. RESULTS AND DISCUSSION 25 4.1 X-ray Diffraction Analysis (XRD) 25 4.2 SEM 27 4.3 Raman Spectroscopy 28 4.4 Photoluminescence Spectroscopy 32 4.5 UV-Vis Spectroscopy 34 4.6 EPR Spectroscopy 35 5. SUPERCAPACITOR DEVICE TEST 39 5.1 Electrical Impedance Spectroscopy 39 v 5.2 Cyclic Voltammetry 40 6. CONCLUSIONS 43 7. FUTURE WORKS 45 8. REFERENCES 46 vi LIST OF FIGURES Figure 1. The flow of energy and the placement of supercapacitors in it. ............................. 2 Figure 2. Overview of the types and classification of supercapacitors. ................................. 4 Figure 3. Classification of electrochemical double layer capacitors (EDLC)1. ..................... 5 Figure 4. Classification of pseudocapacitors.1 ....................................................................... 9 Figure 5. Classification of hybrid supercapacitor into three types according to their design or working mechanism.1 ....................................................................................................... 11 Figure 6. The top part of the figure shows the schematic for the asymmetric supercapacitor design. The photograph at the bottom displays the actual setup built during the experiment. ............................................................................................................................................... 14 Figure 7. An overview of the focus and loci of the active material in our device. The schematic circuit diagrams represent of a rough estimation of two capacitors in series and the sudden jump in their capacitances at the surface level of the active electrode. .............. 15 Figure 8. The hexagoanal wurtzite ZnO crystal structure.52 ................................................ 18 Figure 9. The preparation method for nanoparticles. ........................................................... 19 Figure 10. The steps and procedures taken to produce nanourchins. ................................... 20 Figure 11. The step taken during preparation of nanoflowers. ............................................ 22 Figure 12. Powder X-ray diffraction patterns of ZnO nanostructures. All the indexed peaks in the obtained spectra are matched with the planes of the ZnO hexagonal wurtzite structure (01-079-0207) ....................................................................................................................... 26 Figure 13. Structural and morphological investigation of different ZnO nanostructures. a) EDS spectra of three different nanostructures. The analyses were conducted at 18keV accelerating voltage. b) Secondary-electron SEM micrograph of ZnO nanoflowers, c) Secondary-electron SEM micrograph of ZnO nanourchins, and d) Secondary-electron SEM micrograph of ZnO nanoparticles. All images were recorded through an in-lens detector with an accelerating voltage of 5 keV. In the inset, higher magnification of each image is given. ..................................................................................................................................... 28 Figure 14. First order and second order Raman spectra of three different ZnO nanostructures (λ=532nm). ................................................................................................... 29 Figure 15. The PL intensity versus energy graphs (a-c) for the different ZnO nanostructures. ...................................................................................................................... 33 Figure 16. Tauc-plots (d-f) obtained from UV-Vis reflectance spectra for the different ZnO nanostructures. ...................................................................................................................... 34 Figure 17. (a) Intensity measured at room temperature X band (9.47Hz) EPR and (b) plot of EPR peak to peak intensity with respect to P1/2 for the hydrothermal processed three different nanostructures of ZnO. ..........................................................................................
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