Manikoth M. Shaijumon

Flexible energy storage devices based on nanocomposite paper

There is strong recent interest in ultrathin, flexible, safe energy storage devices to meet the various design and power needs of modern gadgets. To build such fully flexible and robust electrochemical devices, multiple components with specific electrochemical and interfacial properties need to be integrated into single units. Here we show that these basic components, the electrode, separator, and electrolyte, can all be integrated into single contiguous nanocomposite units that can serve as building blocks for a variety of thin mechanically flexible energy storage devices. Nanoporous cellulose paper embedded with aligned carbon nanotube electrode and electrolyte constitutes the basic unit. The units are used to build various flexible supercapacitor, battery, hybrid, and dual-storage battery-in-supercapacitor devices. The thin freestanding nanocomposite paper devices offer complete mechanical flexibility during operation. The supercapacitors operate with electrolytes including aqueous solvents, room temperature ionic liquids, and bioelectrolytes and over record temperature ranges. These easy-to-assemble integrated nanocomposite energy-storage systems could provide unprecedented design ingenuity for a variety of devices operating over a wide range of temperature and environmental conditions.

Coaxial MnO2/Carbon Nanotube Array Electrodes for High-Performance Lithium Batteries

Coaxial manganese oxide/carbon nanotube (CNT) arrays deposited inside porous alumina templates were used as cathodes in a lithium battery. Excellent cyclic stability and capacity of MnO2/CNT coaxial nanotube electrodes resulted from the hybrid nature of the electrodes with improved electronic conductivity and dual mechanism of lithium storage. The reversible capacity of the battery was increased by an order compared to template grown MnO2 nanotubes, making them suitable electrodes for advanced Li ion batteries.

Direct growth of aligned carbon nanotubes on bulk metals

There are several advantages of growing carbon nanotubes (CNTs) directly on bulk metals, for example in the formation of robust CNT–metal contacts during growth. Usually, aligned CNTs1,2,3,4,5,6,7,8,9 are grown either by using thin catalyst layers predeposited on substrates1,2,3,4,5,6,7 or through vapour-phase catalyst delivery7,8,9. The latter method, although flexible, is unsuitable for growing CNTs directly on metallic substrates. Here we report on the growth of aligned multiwalled CNTs on a metallic alloy, Inconel 600 (Inconel), using vapour-phase catalyst delivery. The CNTs are well anchored to the substrate and show excellent electrical contact with it. These CNT–metal structures were then used to fabricate double-layer capacitors and field-emitter devices, which demonstrated improved performance over previously designed CNT structures. Inconel coatings can also be used to grow CNTs on other metallic substrates. This finding overcomes the substrate limitation for nanotube growth which should assist the development of future CNT-related technologies.

Hybrid Nanostructures for Energy Storage Applications

Materials engineering plays a key role in the field of energy storage. In particular, engineering materials at the nanoscale offers unique properties resulting in high performance electrodes and electrolytes in various energy storage devices. Consequently, considerable efforts have been made in recent years to fulfill the future requirements of electrochemical energy storage using these advanced materials. Various multi-functional hybrid nanostructured materials are currently being studied to improve energy and power densities of next generation storage devices. This review describes some of the recent progress in the synthesis of different types of hybrid nanostructures using template assisted and non-template based methods. The potential applications and recent research efforts to utilize these hybrid nanostructures to enhance the electrochemical energy storage properties of Li-ion battery and supercapacitor are discussed. This review also briefly outlines some of the recent progress and new approaches being explored in the techniques of fabrication of 3D battery structures using hybrid nanoarchitectures.

MoS2 Quantum Dot-Interspersed Exfoliated MoS2 Nanosheets

We report the synthesis of heterodimensional nanostructures of MoS2 quantum dots interspersed in few-layered sheets of MoS2, using a liquid exfoliation technique in organic solvents. This unique hybrid morphology results from the optimized experimental conditions involving bath sonication followed by ultrasound probe sonication. We show that such heterodimensional hybrid materials could easily be extracted from the solvent as precipitates when post-treated with less polar volatile solvents such as chloroform. Such tailored MoS2 nanostructures, when directly used as electrodes for hydrogen evolution reaction, showed excellent electrocatalytic activity with low overpotential. Hence, we believe this could lead to large-scale synthesis of liquid-exfoliated layered nanostructures for their potential applications.

Covalently Interconnected Three- Dimensional Graphene Oxide Solids

The creation of three-dimensionally engineered nanoporous architectures via covalently interconnected nanoscale building blocks remains one of the fundamental challenges in nanotechnology. Here we report the synthesis of ordered, stacked macroscopic three-dimensional (3D) solid scaffolds of graphene oxide (GO) fabricated via chemical cross-linking of two-dimensional GO building blocks. The resulting 3D GO network solids form highly porous interconnected structures, and the controlled reduction of these structures leads to formation of 3D conductive graphene scaffolds. These 3D architectures show promise for potential applications such as gas storage; CO2 gas adsorption measurements carried out under ambient conditions show high sorption capacity, demonstrating the possibility of creating new functional carbon solids starting with two-dimensional carbon layers.

Synthesis of hybrid nanowire arrays and their application as high power supercapacitor electrodes

Arrays of multi-segmented hybrid nanostructures of carbon nanotube and gold nanowires have been synthesized using a combination of chemical vapour deposition and electrodeposition methods and we further demonstrate that ultra-high power electrochemical double layer capacitors can be engineered using these hybrid nanowires, resulting in very high power densities.

Conformal Coating of Thin Polymer Electrolyte Layer on Nanostructured Electrode Materials for Three-Dimensional Battery Applications

Various three-dimensional (3D) battery architectures have been proposed to address effective power delivery in micro/nanoscale devices and for increasing the stored energy per electrode footprint area. One step toward obtaining 3D configurations in batteries is the formation of core-shell nanowires that combines electrode and electrolyte materials. One of the major challenges however in creating such architectures has been the coating of conformal thin nanolayers of polymer electrolytes around nanostructured electrodes. Here we show conformal coatings of 25-30 nm poly(methyl methacralate) electrolyte layers around individual Ni-Sn nanowires used as anodes for Li ion battery. This configuration shows high discharge capacity and excellent capacity retention even at high rates over extended cycling, allowing for scalable increase in areal capacity with electrode thickness. Our results demonstrate conformal nanoscale anode-electrolyte architectures for an efficient Li ion battery system.

Platinum/multiwalled carbon nanotubes-platinum/carbon composites as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell

Pt-loaded multiwalled carbon nanotubes (Pt/MWCNTs) have been prepared by chemical reduction method using functionalized MWCNT synthesized by pyrolysis of acetylene over MmNi2 (Mm denotes misch metal) hydride catalyst. Composites of Pt/MWCNT and commercial Pt-loaded carbon black (Pt∕C) have been used as electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cell (PEMFC). Cathode catalyst with 50% Pt/MWCNT and 50% Pt∕C showed best performance due to better dispersion and good accessibility of MWCNT support and Pt electrocatalysts for oxygen reduction reaction in PEMFC. A maximum performance of 540mV at a current density of around 535mAcm−2 has been obtained.

Alloy hydride catalyst route for the synthesis of single-walled carbon nanotubes, multi-walled carbon nanotubes and magnetic metal-filled multi-walled carbon nanotubes

This paper presents a novel, cost-effective and single-step technique for the synthesis of single-walled carbon nanotubes (SWNTs), multi-walled carbon nanotubes (MWNTs) and magnetic metal-filled MWNTs using a fixed bed reaction thermal chemical vapour deposition (CVD) using alloy hydride catalyst. The single-step method involves the pyrolysis of methane at suitable temperatures over fine powders of certain Mischmetal-based AB3 alloy hydride catalysts, prepared through the hydrogen decrepitation technique. These carbon nanostructures have been characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), energy dispersive x-ray analysis (EDAX), thermo-gravimetric analysis (TGA) and Raman spectroscopy. The magnetic properties of these metal-filled MWNTs have been studied by vibrating sample magnetometry, and the results are discussed.