"Despite advancement in the field, energy storage technology has plateaued in recent years. With Li-ion batteries likely reaching the peak of their capability, researchers are developing new technologies such as supercapacitors and other hybrid energy storage devices. Current electrodes for supercapacitors consist primarily of carbon material, such as activated carbon, graphite, graphene, and functionalized multi-walled carbon nanotubes (f-MWCNT). f-MWCNTs are a promising nanomaterial due to their high power density, low cost, low toxicity, high stability, good electrical conductivity, and high active specific surface area (area per mass). The major disadvantage of MWCNT supercapacitors is their lower energy density relative to commercial batteries. However, the addition of metal oxides such as MnO and CoO to f-MWCNT electrodes, can provide a cost-effective energy density boost to supercapacitors through pseudocapacitive effects, while still maintaining the attractive properties of pure f-MWCNT electrodes. This thesis investigates charge storage/delivery properties of Mn/Co-oxides with the aim of using them to functionalize f-MWCNTs and increase the electrode material capacitance.It was found that by functionalizing f-MWCNT with Mn/Co-oxides, a significant increase in specific capacitance was achieved. In galvanostatic charge/discharge (GCD) tests run at 0.2 mA/cm2 the f-MWCNT yielded 288±10F/g, while the Mn0.5/Co0.5-oxide/f-MWCNT electrode yielded 430±14 F/g. Cyclic voltammetry (CV) tests yielded even higher values at low scan rate, 752±85 F/g. It was also found that pure Mn0.5/Co0.5-oxide behaves more as a battery electrode material than as a supercapacitor electrode material, yielding apparent capacitance of 4497±57 mF/cm2 (1.38mAh/cm2). The high apparent capacitance (e.g. energy storage and delivery) was due to intercalation of cations (Na+ or Li+) into the crystalline structure of the Mn0.5/Co0.5-oxide phase in order to compensate the redox transition change. However, the Mn0.5/Co0.5-oxide/f-MWCNT electrodes were not found to enable cation intercalation, and the resulting capacitance was lower (752±85 F/g). All samples showed high stability and highly porous microstructure. Metal oxides were found to consist of MnO, MnO2, CoO, Co3O4 and metal hydroxides." --

"This Ph.D. thesis presents a comprehensive analysis of the potential use of plasma-modified multi-walled carbon nanotube (MWCNT) electrodes for alternative energy storage in electrochemical devices. Over the course of the project, established simple and controllable plasma processes were optimized in order to modify MWCNTs grown in-house. This was done to achieve an enhancement in the electrochemical performance of the materials for their intended applications, specifically, electrocatalyst cathodes for alkaline hydrogen electrolyzers and electrodes for electrochemical capacitors. An inexpensive, scalable thermal chemical vapour deposition (t-CVD) process was used to grow MWCNTs directly from commercially available grade 316 stainless steel (SS) mesh. The diameter of the MWCNTs was large enough such that they were strongly rooted into the SS, allowing for robustness during and after immersion in strong alkaline electrolytes. High purity MWCNTs grown by t-CVD formed dense, yet open, 3-dimensional porous matrices containing large quantities of defect sites. These defect sites are speculated as being excellent anchor points for modification by either physical decoration by metallic nanoparticles (NPs) or covalent bonding of organic functionalities. Ni NPs were immobilized onto MWCNT/SS electrode surfaces using nanosecond (ns) pulsed laser ablation (PLA). The high aspect ratios and relatively open MWCNT matrix allowed for a high area support on which electrocatalyst NPs could be fixed. These Ni NP/MWCNT cathodes were shown to have a high electrocatalytic activity towards the hydrogen evolution reaction in 1 M KOH electrolyte. The mass of Ni NPs was correlated with ablation time and showed optimum performance and repeatability when tPLA = 40 min (0.07 ± 0.01 mg cm−2). Plasma functionalization using an Ar/O2/C2H6 gas mixture was found to covalently graft oxygen-containing carbon surface functionalities (primarily carboxylic groups) to the MWCNT surfaces to produce functionalized MWCNTs (f-MWCNTs). In addition to increasing the hydrophilicity of the MWCNT/SS electrodes, when submersed in 4 M NaOH electrolyte, the f-MWCNTs showed an extreme enhancement in the specific capacitance values, obtaining a 6.7-fold increase over non-functionalized MWCNTs (nf-MWCNTs; 43 ± 5 F g−1 vs 288 ± 10 F g−1 at a current density of 0.2 mA cm−2). The capacitance of the f-MWCNTs was further enhanced by the addition of pseudocapacitive Ir0.4Ru0.6-oxide mixed metal oxide coatings. The Ir0.4Ru0.6-oxide/f-MWCNT electrodes achieved specific capacitances greater than 660 F g−1 at a current density of 0.5 mA cm−2. The excellent electrochemical performance of the plasma-modified MWCNTs coupled with their simple synthesis methods make them ideal candidates for alternative electrochemical energy storage systems." --

This book contains 35 review articles on nanoscience and nanotechnology that were first published in Nature Nanotechnology, Nature Materials and a number of other Nature journals. The articles are all written by leading authorities in their field and cover a wide range of areas in nanoscience and technology, from basic research (such as single-molecule devices and new materials) through to applications (in, for example, nanomedicine and data storage).

All-multiwall carbon nanotube (MWNT) thin films are created by layer-by-layer (LbL) assembly of surface functionalized MWNTs. Negatively and positively charged MWNTs were prepared by surface functionalization, allowing the incorporation of MWNTs into highly tunable thin films via the LbL technique. The pH dependent surface charge on the MWNTs gives this system the unique characteristics of LbL assembly of weak polyelectrolytes, controlling thickness and morphology with assembly pH conditions. We demonstrate that these MWNT thin films have randomly oriented interpenetrating network structure with well developed nanopores using SEM, which is an ideal structure of functional materials for various applications. LbL-MWNT electrodes show high electronic conductivity in comparison with polymer composites with single wall nanotubes, and high capacitive behavior in aqueous electrolyte with precise control of capacity. Of significance, additive-free LbL-MWNT electrodes with thicknesses of several microns can deliver high energy density (200 Wh/kg) at an exceptionally high power of 100 kW/kg in lithium nonaqueous cells. Utilizing the redox reactions on the surface functional groups in a wide voltage window (1.5 - 4.5 V vs. lithium) in nonaqueous electrolytes, asymmetric electrochemical capacitors consisting of LbL-MWNT and either lithium or a lithium titanium oxide negative electrode exhibit gravimetric energy density -5 times higher than conventional electrochemical capacitors with comparable gravimetric power and cycle life. Thin-film LbL-MWNT electrodes could potentially lead to breakthrough power sources for microsystems and flexible electronic devices such as smart cards and ebook readers, while thicker LbL-MWNT electrodes could expand the application of electrochemical capacitors into heavy vehicle and industrial systems, where the ability to deliver high energy at high power will be an enabling technological development. Furthermore, nanoscale pseuduocapactive oxides and electrocatalysts were incorporated into LbL-MWNT electrodes for energy storage and conversion. Inorganic oxides such as MnO2 and RuO2 are incorporated to increase volumetric capacitance in LbLMWNT electrodes using electroless deposition and square wave pulse potential deposition methods. Preliminary results show that we can increase volumetric capacitance of LbLMWNT/ MnO2 and LbL-MWNT/RuO2 composite up to 1000 F/cm3 in aqueous electrolytes. In addition, Pt and Pt/Ru alloy electrocatalysts are introduced into LbL-MWNT electrodes using square wave pulse potential deposition, which show higher CO and methanol oxidation activities. Tailored incorporation of metal and oxide nanoparticles into LbLMWNT electrodes by square wave pulse potential opens a new strategy for novel energy storage and conversion electrodes with superior electrochemical properties.

This thesis examines electrode materials such as mesoporous carbons, manganese oxides, iron oxides and their nanohybrids with graphene. It also explores several of the key scientific issues that act as the governing principles for future development of supercapacitors, which are a promising class of high-efficiency energy storage devices for tackling a key aspect of the energy crisis. However, critical technical issues, such as the low energy density and reliability, need to be addressed before they can be extended to a wide range of applications with much improved performance. Currently available material candidates for the electrodes all have their disadvantages, such as a low specific capacitance or poor conductivity for transition metal oxide/hydroxide-based materials. This thesis addresses these important issues, and develops a high-performance, flexible asymmetric supercapacitor with manganese oxides/reduced graphene oxide as the positive electrode and iron oxide/reduced graphene oxide as the anode, which delivers a high energy density of 0.056 Wh cm-3.

Metal Oxides in Supercapacitors addresses the fundamentals of metal oxide-based supercapacitors and provides an overview of recent advancements in this area. Metal oxides attract most of the materials scientists use due to their excellent physico-chemical properties and stability in electrochemical systems. This justification for the usage of metal oxides as electrode materials in supercapacitors is their potential to attain high capacitance at low cost. After providing the principles, the heart of the book discusses recent advances, including: binary metal oxides-based supercapacitors, nanotechnology, ternary metal oxides, polyoxometalates and hybrids. Moreover, the factors affecting the charge storage mechanism of metal oxides are explored in detail. The electrolytes, which are the soul of supercapacitors and a mostly ignored character of investigations, are also exposed in depth, as is the fabrication and design of supercapacitors and their merits and demerits. Lastly, the market status of supercapacitors and a discussion pointing out the future scope and directions of next generation metal oxides based supercapacitors is explored, making this a comprehensive book on the latest, cutting-edge research in the field. Explores the most recent advances made in metal oxides in supercapacitors Discusses cutting-edge nanotechnology for supercapacitors Includes fundamental properties of metal oxides in supercapacitors that can be used to guide and promote technology development Contains contributions from leading international scientists active in supercapacitor research and manufacturing

Electrochemical capacitors are being increasingly introduced in energy storage devices, for example, in automobiles, renewable energies, and mobile terminals. This book includes five high-quality papers that can lead to technological developments in electrochemical capacitors. The first paper describes the effect of the milling degree of activated carbon particles used in the electrodes on the supercapacitive performance of an electric double-layer capacitor. The second, fourth, and fifth papers describe novel electrode materials that have the potential to enhance the performance of next-generation electrochemical capacitors. Nickel molybdate/reduced graphene oxide nanocomposite, copper-decorated carbon nanotubes, and nickel hydroxide/activated carbon composite are tested, and are shown to be promising candidates for next-generation electrochemical capacitors. The third paper reports the hybrid utilization of electrochemical capacitors with other types of energy devices (photovoltaics, fuel cells, and batteries) in a DC microgrid, which ensures wider applications of electrochemical capacitors in the near future. The knowledge and experience in this book are beneficial in manufacturing and utilizing electrochemical capacitors. Cutting-edge knowledge related to novel electrode nano-materials is also helpful to design next-generation electrochemical capacitors. This book delivers useful information to specialists involved in energy storage technologies.