The Pennsylvania State University The Graduate School College of Earth and Mineral Sciences SCALABLE SYNTHESIS OF GRAPHENE BASED HETEROSTRUCTURES AND THEIR USE IN ENERGY SENSING, CONVERSION AND STORAGE A Dissertation in Material Science and Engineering by Ganesh Rahul Bhimanapati 2017 Ganesh Rahul Bhimanapati Submitted in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy May 2017 ii The dissertation of Ganesh Rahul Bhimanapati was reviewed and approved* by the following: Joshua A Robinson Associate Professor in Material Science and Engineering Dissertation Advisor Chair of Committee James Adair Professor in Material Science and Engineering, , Biomedical Engineering and Pharmacology Tom Mallouk Professor in Chemistry, Biochemistry and molecular biology, Physics and Engineering science and Mechanics. Mauricio Terrones Professor in Physics, Chemistry and Material Science & Engineering Susan Mohney Graduate Program Head, Professor in Material Science & Engineering *Signatures are on file in the Graduate School iii ABSTRACT 2D materials are a unique class of materials system which has spread across the entire spectrum of materials including semi-metallic graphene to insulating boron nitride. Since graphene there has been many other 2D material systems (such as boron nitride (hBN), transition metal dichalcogenides (TMDs)) that provide a wider array of unique chemistries and properties to explore for applications specifically in optoelectronics, mechanical and energy applications. Specifically tailored heterostructures can be made which can retain the character of single-atom thick sheets while having an entirely different optical and mechanical properties compared to the parent materials. In the current work, heterostructures based on graphene, hBN and TMDs have been made, which were used to study the fundamental process-property relations and their use in energy conversion and storage have been studied. The first part of this dissertation focusses on scalable approach for liquid phase exfoliation of graphene oxide (GO) and hBN (Chapter 2). The current work successfully shows an exfoliation efficiency of ~25% monolayer material for hBN, which was not previously achieved. These exfoliated materials were further mixed in the liquid environment to form a new heterostructure BCON (Chapter 3). This newly formed heterostructure was studied in detail for its process-property relations. At pH 4-8, BCON was highly stable and can be dried to form paper or ribbon like material. New bonds were observed in BCON which could be linked to the GO linkage at the nitrogen sites of the hBN. This free standing BCON was tested under various radiation sources like x-rays, alpha, beta, gamma sources and heavy ion like Ar particles and was found that it is very robust to radiation (Chapter 5). By understanding the chemistry, stability and properties of these materials, this could lay a foundation in using these materials for integration in iv conductive and insulating ink development, polymer composite development to improve the thermal and mechanical properties. Another major focus of this dissertation work is combining TMDs and graphene for energy applications specifically hydrogen evolution reactions (HERs) and Lithium ion batteries (LiBs). TMD’s specifically MoS2 and WSe2 were grown on graphite paper using powder vaporization and metal organic chemical vapor deposition (MOCVD) (Chapter 4). Control over the architecture of the MoS2 and WSe2 was achieved by varying the precursor concentration and pressure, which was observed by using scanning electron microscopy. These samples were further characterized using cross-sectional transmission electron microscopy, x-ray photoelectron spectroscopy and Raman microscopy confirming the high quality of the material that was grown. The MoS2/graphite flowers were tested for hydrogen evolution reactions and were found that they are highly active for catalysis and by modifying the surface using simple UV-Ozone treatments, this activity can be increased by 4x (reducing the Tafel slope from 185 to 54 mV/Dec). Similar performance was observed for WSe2/Graphite heterostructure where the tiny 100 nm vertical flakes on graphite paper showed one of the lowest reported Tafel slope of 64 mV/Dec (Chapter 6). MoS2/Graphite was further tested for lithium ion batteries and was found that it had a higher cyclic capacity of 750 mV/Dec. This enhanced stability and performance for energy applications was achieved because of the direct growth technique on graphite. Hence this technique could be used as a scalable alternative to make anodes for lithium ion batteries. v TABLE OF CONTENTS List of Figures ................................................................................................................................ ix List of Tables ................................................................................................................................ xx List of Symbols/acronyms .......................................................................................................... xxi Acknowledgements .................................................................................................................. xxvii Chapter 1 INTRODUCTION/ LITERATURE REVIEW ................................................ 1 What is a 2D Material? ............................................................................................... 1 Graphene? ..................................................................................................................... 1 History and Structure evolution ............................................................................................... 1 Beyond Graphene Materials: Introduction .............................................................................................. 4 Inorganic 2D Materials .............................................................................................................. 7 Introduction To Boron Nitride ................................................................................................. 7 Structure And Properties Of 2D Boron Nitride ..................................................................... 8 Synthesis Of BNNS ................................................................................................................. 13 Mechanical Exfoliation ........................................................................................................... 13 Solvent assisted ultra-sonication ............................................................................................ 17 Acid Exfoliation ....................................................................................................................... 20 Chemical Functionalization of h-BN ..................................................................................................... 20 Single And Few-Layer h-BN Via Chemical Vapor Deposition ......................................................... 25 Transition Metal Dichalcogenides ......................................................................................................... 33 Large-Area, Morphology-Controlled Synthesis of TMDs ................................................. 35 Synthesis of 2D-TMD Heterostructures ............................................................................... 37 TMD’s and Graphene based materials for Hydrogen evolution reactions and Lithium ion batteries ...................................................................................................................................................... 39 Current Research Focus ........................................................................................................................... 42 vi Chapter 2 Exfoliation and Functionalization of Graphene oxide and Hexagonal Boron Nitride ......................................................................................... 45 Introduction ............................................................................................................................................... 45 Exfoliation of Graphene Oxide (GO) ................................................................................................... 46 Synthesis Procedure .................................................................................................................. 46 Structural and Chemical characterization of GO ................................................................... 48 Exfoliation of Hexagonal Boron Nitride (hBN) .................................................................................. 49 Synthesis Procedure ................................................................................................................. 49 Structural Characterization of hBN ....................................................................................... 50 XRD analysis ........................................................................................................................... 55 Thickness Characterization of hBN ....................................................................................... 56 Chemical Functionalization Study of exfoliated hBN ....................................................................... 58 X-ray Photoelectron Spectroscopic analysis ........................................................................ 58 Fourier transform Infra-red spectroscopy analysis .............................................................. 62 Chapter 3 Liquid Phase synthesis