Browsing by Author "Vinod, Soumya"

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    2D material integrated macroporous electrodes for Li-ion batteries
    (Royal Society of Chemistry, 2017) Gullapalli, Hemtej; Kalaga, Kaushik; Vinod, Soumya; Rodrigues, Marco-Tulio F.; George, Antony; Ajayan, Pulickel M.
    Three-dimensionally structured architectures are known to improve the performance of electrodes used in Li ion battery systems. In addition, integration of select 2D materials into 3D structures, for enhancing both electrical conductivity and electrochemical activity, will prove advantageous. Here a scalable one-step chemical vapor deposition technique is demonstrated for the controlled etching and simultaneous graphene growth on stainless steel substrates resulting in a 3D micro-mesh architecture that is ideal for high rate/high capacity electrodes; the graphene coated 3D stainless steel current collector is used with an MoS2 electrode material for demonstrating high stability and rate capacity in Li-ion batteries.
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    Three Dimensional Engineered Structures from Graphene Oxide Atomic Layers
    (2016-04-20) Vinod, Soumya; Pulickel, Ajayan
    Two dimensional (2D) atomic layered materials have recently gained much attention due to their novel physical properties. However, to be utilized for direct applications, there is a need to build three dimensional (3D) structures from them that can retain the intrinsic properties of the material while leading to novel behavior originating from the macroscopic assembly. Graphene, the first 2D material to be discovered, have unique set of properties that have led to numerous studies. While most initial applications of graphene concentrated on creating high quality single layer graphene, further unraveling its potential in multifunctional use demanded large scale production for creating 3D structures. This brought into prominence Graphene Oxide (GO) that has graphene layers with oxygen functionalities present on basal planes and edges and could be synthesized in large quantities by chemical approaches. Originally, the major advantage of GO was as an intermediate compound for mass producing graphene through chemical reduction. However, GO by itself was found to demonstrate exciting properties as a result of the structure and functional groups present. GO has emerged as a major precursor in creating various engineered carbonaceous materials. In this work, GO is used as the fundamental unit for building macroscopic systems such as foam, film and composite with detailed analysis of their formation and properties. Chapter 1 discusses the emergence of 2D materials, the popularity of graphene based materials and their use as building blocks for creating 3D structures. Background studies on GO is provided and their advantages to be used as precursor in developing 3D materials are reviewed. The final section of the chapter focuses on the experimental methods used for synthesis and characterization of the different 3D structures built from GO. In Chapter 2, unique structural formation of a foam from the interaction of GO and hexagonal boron nitride (h-BN) is investigated. Electron microscope imaging and mechanical characterization provide insights into the formation and the mechanical response of the foam. The novel orderly stacked layered architecture demonstrates enhanced mechanical strength and structural stability even at increased temperature. In Chapter 2, free standing GO films consisting tightly packed GO layers are synthesized and the effect on the sliding of layers due to the interaction of oxygenated species present is investigated. A new mechanism of stick-slip motion that translates to strain rate dependent plasticity where the GO film behavior transitions from brittle to ductile with decrease in strain rate is observed. Chapter 3 explores GO as a substitute for epoxies in two part epoxy systems towards synthesizing thermally conducting epoxies. The interactions of the epoxy functional groups in GO with polymercaptan based epoxy hardener forms a thermosetting resin that provides high thermal stability and adhesion between surfaces. This elevates GO as the main constituent in the epoxy system and eliminates its limitation as a filler material. The implications of the material for thermal management applications are discussed. Chapter 5 summarizes the findings and reviews the challenges associated with building controlled macroscopic architecture from 2D fundamental units followed by future advancement directions.