Microwave Enabled Fabrication Of Highly Conductive Graphene And Porous Carbon Metal Hybrids For Sustainable Catalysis And Energy Storage

Carbon is the most abundant material next to oxygen in terms of sustainability. The potential of carbon based materials has been recognized in recent decades by the discovery of fullerene (1996 Nobel prize in chemistry), carbon nanotubes (2008 Kavli prize in nanoscience) and graphene (2010 Nobel prize in physics). The synthesis of carbon materials with well controlled morphologies lead to their exploration in both fundamental research and industrial applications. Graphene also commonly referred to as a wonder material has been under extensive research for more than a decade, due to its excellent electronic, optical, thermal and mechanical properties. However, the realization of these applications for practical purposes require its large scale synthesis. The common method of graphene synthesis involves reduction of graphene oxide. Nevertheless, complete restoration of intact graphene basal plane destroyed by oxidation cannot be achieved, limiting the application of as synthesized graphene in flexible macro electronics, mechanically and electronically reinforced composites etc. Hence, research was pursued in regards to achieve controlled oxidation, sufficient enough to overcome the Vander-Waals forces and preserving the graphene domains. One such approach reported by our group is the solution processable graphene achieved via controlled oxidation, by the use of nitronium oxidation approach. However, toxic NOx gases and byproducts generated during the synthesis, limits the scalability of this approach. In this thesis, for the first time, we reported the synergy of piranha etching solution with intercalated graphite for the controlled oxidation of graphite particles via microwave heating in chapter 2. The controlled oxidation leads to rapid (60 seconds) and direct generation of highly conductive, clean low oxygen containing graphene sheets without releasing any detectable toxic gases or aromatic by-products as demonstrated by gas chromatography-mass spectrometry. These highly conductive graphene sheets have unique molecular structures, different from both graphene oxide and pristine graphene sheets. They can be dispersed in both aqueous and common organic solvents without surfactants/stabilizers producing "clean" graphene sheets in solution phase. "Paper-like" graphene films are generated via simple filtration resulting in films with a conductivity of 2.26 × 104 S m-1, the highest conductivity observed for graphene films assembled via vacuum filtration from solution processable graphene sheets to date. After 2-hour low temperature annealing at 300 C, the conductivity further increased to 7.44 × 104 S m-1. This eco-friendly and rapid approach for scalable production of highly conductive and "clean" solution-phase graphene sheets would enable a broad spectrum of applications at low cost. Irrespective of the vast applications of highly conductive graphene, it exhibits limited catalytic centers, is impervious, and limits the diffusion of ions. This inadequacy can be overcome by the hole generation on highly conductive graphene. Current approaches for large scale production of holey graphene require graphene oxide (GO) or reduced GO (rGO) as starting materials. Thus generated holey graphene derivatives still contain a large number of defects on their basal planes, which not only complicates fundamental studies, but also influences certain practical applications due to their largely decreased conductivity, thermal and chemical stability. This work reports a novel scalable approach exploiting the wireless joule heating mechanism provided by microwave irradiation of partially oxidized graphite intercalation compounds in chapter 3. The wireless joule heating mechanism affords region-selective heating, which not only enable fabrication of holey graphene materials with their basal plane nearly intact, but also engineers the edges associated with holes to be rich in zigzag geometry. The term pristine holey graphene was given, to differentiate from the holey graphene derivatives with basal plane defects, as reported in the literature. The pristine holey graphene with zigzag edges were studied and explored as a metal free catalyst for reduction reactions via hydrogen atom transfer mechanism. The pristine holey graphene nanoplatelets not only exhibited high catalytic activity and desired selectivity, but also provided excellent chemical stability for recyclability, which is very different from its counterpart holey graphene derivatives with basal plane defects. It was also reported that the reduction of nitrobenzene occurs via condensation pathway with this catalyst. To further provide insight into combustion of graphite in air with microwave irradiation, the stabilized intercalated graphene without point defects was used to generate holes in chapter 4. The co-intercalated O2 into graphite intercalated compound act as the internal oxidant, to oxidize the carbon, along with the surrounding air. High local temperatures were achieved via joule heating mechanism, hence promoting combustion of graphene to generate holes and edges. We observed that in combination to hole generation, higher conductivity was also observed in comparison to the holey graphene synthesized in chapter 3. The highly conductive holey graphene was tested for their electro-catalytic activity in the reduction of oxygen. The reduction of oxygen occurs via 2e- pathway, where peroxide with 90% yield was recorded. This opens path for onsite peroxide production in alkaline media, and therefore allowing its use in bleaching industries. In concern of carbon based materials being explored for catalysis, their high amount to facilitate the reaction, limits practicality of the catalyst for industrial applications. However, the immobilization of metal nanoparticles onto porous carbon supports, synthesized from sustainable and cheap biomass was widely pursued. It was widely reported that the doping of carbon support with N further improved their interaction with the metal and promoted higher catalytic activity. In chapter 5, for the first time, the influence of P doped carbon support on catalytic activity of Pd was reported. A single step microwave assisted fabrication of Pd embedded into porous phosphorous doped graphene like carbon was demonstrated. Structural characterization revealed that, the metal nanoparticles are in the range of 10nm with a surface area of 1133m2/g. The developed method is not only sustainable as it is synthesized from biomass and anti-nutrient molecule (phytic acid), but also energy efficient as microwave irradiation (50sec) is used for the catalyst synthesis. The as synthesized catalyst recorded 90% conversion with a TOF of 23000h-1 for benzyl alcohol oxidation, which remained constant even after 8 recycles indicating the stability of catalyst. Different wt% of Pd onto PGC was tested for their alcohol oxidation capacity and found that the 3% Pd-PGc which activates O2 more towards 4e- in ORR has the best conversion and selectivity. The biomass molecule phytic acid used for the synthesis of phosphorous doped carbon support was also used as a phosphorous source in the synthesis of tin phosphides in chapter 6. Current studies have shown that sodium, a low cost and naturally abundant metal, can act as a substituent for lithium in lithium ion batteries (LIB), hence, allowing their applications in real world. This transition towards the use of sodium ion batteries (SIB) has entailed research to improve the cycle stability and energy density of battery by introducing tin phosphides as anodes for batteries. Tin phosphides exhibit a self-healing mechanism, hence decreases the capacity decay as observed in the case of Sn metal. However, it was reported that the self-healing mechanism is not completely reversible with partial pulverization observed. Therefore, we pursued a time efficient method to synthesize tin phosphide in a phosphorous doped carbon matrix (SnP@PGc) via microwave irradiation. The SnP@PGc formed when tested as anode for SIBs, demonstrated superior capacity of 515 mAh/g after 750 cycles at a charge and discharge current of 0.2 C. The superior cycle stability can be attributed to the protection against volume expansion by phosphorous doped porous carbon shell during battery charge and discharge process and hence mitigating the pulverization of tin phosphides.

Carbon nanotubes (CNTs) and graphene are the two most conductive members among carbon nanomaterials. For industrial applications, these nanomaterials are attracting great attention for fabrication of flexible conducting films. However, the electronic performance of either CNT or graphene film has yet to reach their theoretical expectations due to high resistance and tunneling/Schottky barriers at the junctions between nanotubes or between graphene sheets. One of the important observations was that CNTs and graphene sheets can be crosslinked during and/or after film fabrication, which largely decrease inter-tube or inter-sheet resistance. However, the current solution-processing techniques for the film fabrication, such as spin coating, layer-by-layer assembly, and vacuum filtration have disadvantages and limitations. In this thesis, we developed an efficient film assembly approach as well as a facile transfer process. The first chapter of this thesis provides an overview on structure and properties of CNTs and graphene. In the second chapter, we used our newly developed microwave-enabled dispersion technique to synthesize highly conductive dispersible CNTs and graphene with low-density of oxygen-containing groups, without a need of surfactant/stabilizer. As we fabricated Microwave-enabled low-oxygen multi-walled nanotube only (ME-LOMWNT-only), Microwave-enabled low-oxygen graphene only (ME-LOGr-only), and ME-LOMWNT/ME-LOGr hybrid films using vacuum filtration, we found that the hybrid films are highly conductive relative to either the ME-LOMWNT-only or ME-LOGr-only film. The conductivity of the hybrid films depends on their composition, where a weight ratio of 97/3 between MWNTs and graphene reached the highest conductivity of 247,812 S m-1, which is two times higher than those of SWNT/graphene hybrid films reported by Coleman et al. 8 In this work, we found crosslinks between MWNTs and graphene, which could be further promoted in acidic environment. These crosslinks between MWCNT and graphene enhanced the film conductivity. The aim of the third chapter was to fabricate high quality graphene films and MWNT/graphene hybrid films using interfacial self-assembly approach. We observed the different assembly behavior of ME-LOMWNT and ME-LOGr due to their different shape and surface energy. Then, we optimized the parameters to fabricate high quality of ME-LOMWNT/ME-LOGr hybrid films. Moreover, we developed an efficient approach to transfer the self-assembled film at this water/oil interface onto substrates for future electrical characterization and device fabrications.

Due to its phenomenal mechanical characteristics and remarkable electrical properties, graphene, a perfect single-atomic thick two-dimensional lattice carbon layer, has attracted extensive attention in nanoscience and condensed matter physics. With all the similarities, it is believed that graphene can compete with or even surpass carbon nanotubes in many fields, and it is expected to replace silicon in many electronic applications and in other advanced technologies. A single layer of graphene sheet was first isolated in 2004 from highly oriented pyrolysis graphite with Scotch tape. The invention of "The Scotch-tape" method seems very simple, and it has enabled a whole new path in many graphene-based research areas. It also resulted in Andre Geim and Konstantin Novoselov's winning the 2010 Nobel Prize in physics. This solvent-free method however suffers from low yields, low repeatability, and being extremely labor intensive. Solution-based fabrications have shown to be able to overcome these problems. However, the next challenge in the graphene research field and applications is the tedious chemical path that is required to convert oxidized graphene using toxic chemicals, such as hydrazine. In this thesis, we first developed a novel and an unprecedentedly fast and simple approach to directly exfoliate graphite flakes with the aid of both nitronium ion and microwave irradiation with the aim of solving the main research problems in the field. To utilize the produced graphene in practical applications, our knowledge of interfacial science was exploited to controllably self-assemble these wonderful materials into desired structures. The research results combined with an introduction of the development and future aspects of these fields will be presented in the five chapters of this thesis. Chapter 1 will include a general overview of basic but important information concerning the two main carbon-based materials, carbon nanotubes and graphene. Their structures, physical properties, methods of fabrications and applications will be discussed in depth. In addition, interfacial science for self-assembly of nanomaterials will be summarized. In Chapter 2, an efficient, simple and promising way to prepare graphene sheets directly from graphite flakes with the aid of nitronium ions and microwave irradiation will be presented. Knowledge of the chemistries related to nitronium ions and microwave has enabled us to purposely omit strong oxidants, such as KMnO4, with an aim not to heavily oxidize the materials, as many methods are based on, thus reduction reactions can be completely avoided. Experimental results demonstrate that this non-destructive method resulted in concentrated stable dispersions of flat, high-quality, conductive graphene sheets in both aqueous and organic solvents. This mildly oxidized material was extensively characterized by atomic force microscope (AFM), Infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy, thermo-gravimetric analysis (TGA), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). In chapter 3, we extended the nitronium ions and microwave enabled dispersed approach to carbon nanotubes. Different sources of both single-walled carbon nanotubes (SWNTs) and multi-walled carbon nanotubes (MWNTs) were tested and the results showed that all the CNTs from different sources can be quickly dispersed into aqueous solutions with remarkably high concentrations compared to those of graphene solutions even though the same parameters were applied during dispersion. We found that depending on the existence of a small amount of defects from the original CNT sources, the yield, and quality of the dispersed CNTs are varied. With a long term aim of fabricating highly transparent and conductive films to replace Indium tin oxide (ITO) in a wide variety of optoelectronic devices, in Chapter 4, a new method referred to as an interfacial self-assembly approach is developed to assemble the microwave dispersed graphene and CNTs into highly conductive films. The self-assembly behavior of graphene, CNT, and a mixture of graphene and CNT with different ratios were studied separately, and the knowledge obtained was used to fabricate graphene, CNT, and a hybrid of graphene-CNT thin films at an oil/water interface, respectively. Compared to the generally used vacuum filtration method, this new approach does not need any membrane, thus theoretically any size film can be easily fabricated. To transfer the formed films to substrates for practical applications, a simple film-transferring method was also developed. The films fabricated with different film fabrication methods will also be compared and a systematic study on how the compositions of these two materials affect the performance of the final films will be summarized. The dispersed graphene sheets are often composed with graphene sheets of different sizes, to separate them for different applications. In Chapter 5, interfacial self-assembly reactions were also applied to separate the graphene sheets based on their size-and electronic-dependent surface energies Chapter 6 will then focus on fine-tuning the surface chemistry of the graphene sheets and the oil/water ratio to efficiently emulsify the graphene sheets into core-shell capsules for drug delivery applications. Poly(N-isopropylacrylamide) (PNIPAA), a thermally sensitive polymer is introduced to form a temperature-sensitive and stable oil-in-water microemulsion with the ability to release the encapsulated materials in a graphene/PNIPAA shell above its transition temperature. Experimental observations show that the emulsion with graphene has a slightly increased transitional temperature from 34 °C to 38 °C.

Comprehensive Energy Systems, Seven Volume Set provides a unified source of information covering the entire spectrum of energy, one of the most significant issues humanity has to face. This comprehensive book describes traditional and novel energy systems, from single generation to multi-generation, also covering theory and applications. In addition, it also presents high-level coverage on energy policies, strategies, environmental impacts and sustainable development. No other published work covers such breadth of topics in similar depth. High-level sections include Energy Fundamentals, Energy Materials, Energy Production, Energy Conversion, and Energy Management. Offers the most comprehensive resource available on the topic of energy systems Presents an authoritative resource authored and edited by leading experts in the field Consolidates information currently scattered in publications from different research fields (engineering as well as physics, chemistry, environmental sciences and economics), thus ensuring a common standard and language

This thesis focuses on the synthesis and characterization of various carbon allotropes (e.g., graphene oxide/graphene, graphene foam (GF), GF/carbon nanotube (CNT) hybrids) and their composites for electrochemical energy storage applications. The coverage ranges from materials synthesis to electrochemical analysis, to state-of-the-art electrochemical energy storage devices, and demonstrates how electrochemical characterization techniques can be integrated and applied in the active materials selection and nanostructure design process. Readers will also discover the latest findings on graphene-based electrochemical energy storage devices including asymmetric supercapacitors, lithium ion batteries and flexible Ni/Fe batteries. Given the unique experimental procedures and methods, the systematic electrochemical analysis, and the creative flexible energy storage device design presented, the thesis offers a valuable reference guide for researchers and newcomers to the field of carbon-based electrochemical energy storage.

Since the first and second industrial revolutions, the development of energy conversion and storage technologies have brought great progress and convenience to modern society. Most of the innovations and technologies focus on the carbon-based fuels such as coal, petroleum and natural gas, which are not only limited resources and but also harmful for the environment. Meanwhile, the power demand from industries and societies has been growing rapidly in the recent years. In this consideration, a number of research efforts have been intensively applied to pursue alternative clean energy resources and new energy storage and conversion systems, such as supercapacitors, lithium-ion batteries, metal-oxygen, water electrolysis and so on. In this dissertation, we report the synthesis and preparation of a series of polymer and nanomaterials with controllable composition and structure, to fit for the specific requirement in different systems and promote the device performance.In order to prevent the aggregation of graphene sheets, we designed a method to fabricate 3D macro porous graphene by using bi-continuous polymer templates. The structure and pore size of the graphene can be controlled by corresponding polymer templates. The resulting graphene monolith materials were used as the supercapacitor electrode and exhibited excellent stability (over 6000 cycles with capacity retention of 98%). This work provides a novel way to fabricate high-quality, macroporous graphene that can be useful in applications such as electrochemical energy storage electrodes and high surface area catalyst scaffolds.To investigate the Li-oxygen battery discharge reaction pathway, patterned Au-nanodots as surface-enhanced Raman substrates are prepared by using a universal method of metal deposition through a nano-shadow mask. The discharge products on different electrodes (graphene and gold) were analyzed and the results indicated that the reaction process on the lithium-air cathode was significantly dependent upon the change of cathode materials. To develop a stable, efficient, non-noble metal-based electrocatalysts for oxygen evolution reaction, we have synthesized hollow and conductive iron-cobalt phosphide (Fe-Co-P) alloy nanostructures using a Fe-Co metal organic complex as a precursor. The Fe-Co-P alloy exhibits excellent OER activity with a specific current density of 10 mA/cm2 being achieved at an overpotential of 252 mV. Our results conclude that the electrochemical-induced high-valent iron stabilizes the cobalt in a low-valent state, leading to the simultaneous enhancement of activity and stability of the OER catalyst.For the purpose of developing high energy storage lithium ion batteries, we have synthesized highly porous Mn3O4/C nanospheres with the hierarchical structure as anode materials by self-assembly to form a spherical Mn-based metal organic complex, followed by a facile thermal annealing process. The Mn3O4/C nanospheres consisted of homogeneously distributed Mn3O4 nanocrystals with a conformal carbon coating. Such a hierarchical, porous structure provided both good electrical conductivity and volume changes accommodation capability. In order to mitigate the dendrite formation on the Li-metal electrode, 2D Ni3 (2,3,6,7,10,11-hexaiminotriphenylene)2 (Ni3 (HITP)2) metal-organic framework was also explored as the nano-host for Li deposition. During cycling, the high intrinsic electrical conductivity of Ni3 (HITP)2 evens potential difference on the Li metal surface and the nano-channel structure enables fast Li-ion and organic molecules through 2D nanosheets and endows nano hosts for Li nucleation and deposition. The 2D conductive MOF modified Li electrode exhibits an excellent coulombic efficiency of 99.95% in the Li/ Li2 Ti5 O12 (LTO) cell for 500 cycles. In order to improve the safety of lithium-ion batteries, we have explored a high yield method to prepare surface-modified glass fiber pillars strengthened shear thickening electrolyte from the conventional Li-ion battery electrolyte. The volume fraction of the fillers could be lowered compared with the spherical fillers due to the high aspect ratio of the glass fiber pillars. The electrochemical stability of this impact resistant electrolyte was further evaluated in the half-cell and full-cell characterizations. Ballistic tests were also carried out to monitor the voltage variation with different impact energies. In this thesis, we have introduced a number of synthesis and preparation methods to fabricate structured polymer and nanomaterials. These materials are employed as electrodes, electrolyte fillers and catalyst by adjusting the composition, structure, and surface of the materials. The fabrication and evaluation of the energy storage and conversion devices (supercapacitors, Li-ion, Li-oxygen batteries, and alkaline water electrolysis) are also included.

Templated Fabrication of Graphene-Based aterials for Energy Applications An illuminating look at the latest research on graphene-based materials and their applications in energy In Templated Fabrication of Graphene-Based Materials for Energy Applications, a team of distinguished materials scientists delivers a unique and topical exploration of a versatile fabrication method used to create high-quality graphene and composites. The book offers a three-part approach to current topics in graphene fabrication. The first part introduces graphene-based materials and is followed by cutting-edge discussions of template methods used in the preparation of graphene-based materials. The editors conclude with the latest research in the area of graphene-based materials applications in various energy-related pursuits. Readers will find relevant content that refers to original research conducted by the editors themselves, as well as work from up-and-coming and established researchers that explores the most interesting horizons in the study of graphene-based materials. The book also provides: A thorough introduction to graphene, including its history and physical properties An in-depth analysis of current graphene synthesis strategies, including the classification of graphene preparations Expansive discussions of various kinds of template methods for graphene production, including the study of porous metals and the preparation of graphene in large quantities Comprehensive explorations of the applications of various graphene-based materials, including lithium-ion batteries, lithium-sulfur batteries, and supercapacitors Perfect for materials scientists, electrochemists, and solid-state physicists, Templated Fabrication of Graphene-Based Materials for Energy Applications will also earn a place in the libraries of physical chemists and professionals in the electrotechnical industry.

The book presents a comprehensive review of graphene-based supercapacitor technology. It focusses on synthesis, characterization, fundamental properties and promising applications of graphene materials and various types of graphene-based composites. The wide range of applications include electric power systems of portable electronics, hybrid-electric vehicles, mobile phones etc. Keywords: Graphene, Energy Storage Materials, Supercapacitors, Micro-Supercapacitors, Self-Healable Supercapacitors, Graphene-Based ZnO Nanocomposites, Defect Engineered Graphene Materials, Electric Power Systems.

The high porosity and openness of metal-organic frameworks (MOFs) have been extensively studied in gas adsorption, catalysis, and the use as templates for nanoporous materials synthesis; but its potential in electrochemical energy storage is not well understood. MOFs consist of redox active metal clusters and tunable pore size, which enable the ability to contribute to pseudocapacitance in electrochemical supercapacitors. Although MOFs are generally considered as poor conductors, doping MOFs with highly conductive graphene sheets can potentially enhance the capacitance in pure graphene capacitive devices. In this study, a four-metal MOF-74 (M4M-MOF-74) was selected to investigate the capacitance enhancement due to its unique coordinately unsaturated metal sites. The MOF-74 bears one dimensional channels that can adsorb H+ and Li+ very well, but not Na+ in aqueous electrolytes, allowing ions of appropriate size to access the framework and to fully interact with the metal sites. Moreover, the MOF/graphene hybrid electrodes demonstrate great conductivity, high areal capacitance, and good stability in an H2SO4 aqueous electrolyte. At a scan rate of 10 mV/s, the hybrid electrode exhibits a high areal capacitance of 54.1 mF/cm2, which is about four times higher than a pure graphene electrode. This work could potentially open up a new application for MOFs in electrochemical capacitors.

• Covers the fabrication of graphene-silicon and graphene-silicon nanowire arrays (SiNWAs) Schottky junction near infrared photodetectors (NIRPDs). • Includes details on the applications of graphene thin film for lithium ion batteries.