Jayan Thomas

Supercapacitor electrode materials: nanostructures from 0 to 3 dimensions

Supercapacitors have drawn considerable attention in recent years due to their high specific power, long cycle life, and ability to bridge the power/energy gap between conventional capacitors and batteries/fuel cells. Nanostructured electrode materials have demonstrated superior electrochemical properties in producing high-performance supercapacitors. In this review article, we describe the recent progress and advances in designing nanostructured supercapacitor electrode materials based on various dimensions ranging from zero to three. We highlight the effect of nanostructures on the properties of supercapacitors including specific capacitance, rate capability and cycle stability, which may serve as a guideline for the next generation of supercapacitor electrode design.

Holographic three-dimensional telepresence using large-area photorefractive polymer

Holography is a technique that is used to display objects or scenes in three dimensions. Such three-dimensional (3D) images, or holograms, can be seen with the unassisted eye and are very similar to how humans see the actual environment surrounding them. The concept of 3D telepresence, a real-time dynamic hologram depicting a scene occurring in a different location, has attracted considerable public interest since it was depicted in the original Star Wars film in 1977. However, the lack of sufficient computational power to produce realistic computer-generated holograms and the absence of large-area and dynamically updatable holographic recording media have prevented realization of the concept. Here we use a holographic stereographic technique and a photorefractive polymer material as the recording medium to demonstrate a holographic display that can refresh images every two seconds. A 50 Hz nanosecond pulsed laser is used to write the holographic pixels. Multicoloured holographic 3D images are produced by using angular multiplexing, and the full parallax display employs spatial multiplexing. 3D telepresence is demonstrated by taking multiple images from one location and transmitting the information via Ethernet to another location where the hologram is printed with the quasi-real-time dynamic 3D display. Further improvements could bring applications in telemedicine, prototyping, advertising, updatable 3D maps and entertainment.

Highly Ordered MnO2 Nanopillars for Enhanced Supercapacitor Performance

This report demonstrates a simple, but efficient method to print highly ordered nanopillars without the use of sacrificial templates or any expensive equipment. The printed polymer structure is used as a scaffold to deposit electrode material (manganese dioxide) for making supercapacitors. The simplicity of the fabrication method together with superior power density and energy density make this supercapacitor electrode very attractive for the next-generation energy storage systems.

An updatable holographic three-dimensional display

Holographic three-dimensional (3D) displays provide realistic images without the need for special eyewear, making them valuable tools for applications that require situational awareness, such as medical, industrial and military imaging. Currently commercially available holographic 3D displays use photopolymers that lack image-updating capability, resulting in restricted use and high cost. Photorefractive polymers are dynamic holographic recording materials that allow updating of images and have a wide range of applications, including optical correlation, imaging through scattering media and optical communication. To be suitable for 3D displays, photorefractive polymers need to have nearly 100% diffraction efficiency, fast writing time, hours of image persistence, rapid erasure, and large area—a combination of properties that has not been shown before. Here, we report an updatable holographic 3D display based on photorefractive polymers with such properties, capable of recording and displaying new images every few minutes. This is the largest photorefractive 3D display to date (4 × 4 inches in size); it can be recorded within a few minutes, viewed for several hours without the need for refreshing, and can be completely erased and updated with new images when desired.

Evolution of nonlinear optical properties: from gold atomic clusters to plasmonic nanocrystals.

Atomic clusters of metals are an emerging class of extremely interesting materials occupying the intermediate size regime between atoms and nanoparticles. Here we report the nonlinear optical (NLO) characteristics of ultrasmall, atomically precise clusters of gold, which are smaller than the critical size for electronic energy quantization (∼2 nm). Our studies reveal remarkable features of the distinct evolution of the optical nonlinearity as the clusters progress in size from the nonplasmonic regime to the plasmonic regime. We ascertain that the smallest atomic clusters do not show saturable absorption at the surface plasmon wavelength of larger gold nanocrystals (>2 nm). Consequently, the third-order optical nonlinearity in these ultrasmall gold clusters exhibits a significantly lower threshold for optical power limiting. This limiting efficiency, which is superior to that of plasmonic nanocrystals, is highly beneficial for optical limiting applications.

Energy Storing Electrical Cables: Integrating Energy Storage and Electrical Conduction

DOI: 10.1002/adma.201400440 approach proposed by Simon and Gogotsi is depositing pseudocapacitive material (like MnO 2 ) onto a nanostructured current collector. [ 9 ] Despite some achievements that have been made by using similar methods, such as depositing MnO 2 onto nanowires, [ 10 ] nanotubes, [ 11 ] and nanopillars, [ 12 ] these arrays usually suffer from structural collapse, resulting in a decrease of useful surface area, reduction of deposited active materials and limited accessibility of electrolyte. Furthermore, these nanostructured current collectors are either derived from expensive and environment-unfriendly template methods or tedious fabrication processes. Therefore, it is still a challenge to readily and simply fabricate nanostructured electrodes with large area, template-free, and high aspect ratio arrays without nanostructures clumping together. Here we developed a large area, template-free, high aspect ratio, and freestanding CuO@AuPd@MnO 2 core-shell nanowhiskers (NWs) design. Our electrochemical measurements show that these CuO@AuPd@MnO 2 NWs exhibit remarkable properties including high specifi c capacitance, excellent reversible redox reactions, and fast charge-discharge ability. Moreover, a novel coaxial supercapacitor cable (CSC) design which combines electrical conduction and energy storage by modifying the copper core used for electrical conduction was demonstrated. For accomplishing large surface area necessary for high supercapacitor performance, we developed NWs on the outer surface of the electrical copper wire. The NWs structure is developed by just heating the inner core and therefore is practical to upscale the process to make extended lengths. An attractive advantage of using the coaxial design is that electricity can be conducted through the inner conductive metal wire and electrical energy can be stored in the nanostructured concentric layers added to this inner metal wire with an oxide layer in between. It is always a vital task for many applications including aviation to fi nd better methods to save weight and space, while maintaining the intended purpose. Therefore, integration of electrical cable and energy storage device into one unit offers a very promising opportunity to transmit electricity and store energy at the same time. In addition, CSC built from these NWs exhibits excellent fl exibility and bendability, superior long-term cycle stability, and high power and energy densities. The development of this innovative lightweight, fl exible, and space saving CSC will be very attractive for many applications including hybrid and allelectric vehicles, electric trains, heavy machineries, aircrafts and military. Fabrication of electrode involves three steps: (1) growth of CuO NWs from a pure copper wire by heat treatment; (2) deposition of a conducting metal layer by sputter-coating; (3) electrodeposition of active material onto the nanostructures ( Figure 1 a). Scanning electron microscope (SEM) image (Figure 1 b) clearly Currently, millions of miles of electrical cables have been used for providing electrical connections in machineries, equipment, buildings and other establishments. Energy storage devices are completely separated from these electrical cables if used. However, it will revolutionize energy storage applications if both electrical conduction and energy storage can be integrated into the same cable. Coaxial cable, also called coax, is one of the most common and basic cable designs that is used to carry electricity or signal. It has an inner conductor enclosed by a layer of electrical insulator, and covered by an outer tubular conducting shield (see Supporting Information, SI, Figure S1). The term “coaxial” is used because both the inner and outer conductors share the same geometric axis. In a coaxial design, it is possible to combine two different functional devices into one device that can still perform the original functions independently. Supercapacitors, also known as electrochemical capacitors, have become one of the most popular energy storage devices in recent years. Compared to other energy storage devices like batteries, supercapacitors have faster charge-discharge rates, higher power densities, and longer life times. [ 1 ] As a signature of their performance, safety, and reliability, they have recently been employed in the emergency doors of Airbus A380. Supercapacitors store energy by Faradaic or non-Faradaic reactions. Supercapacitors which utilize the Faradaic reactions are also called pseudocapacitors. Metal oxides/hydroxides like ruthenium oxide (RuO 2 ), [ 2 ] manganese dioxide (MnO 2 ), [ 3 ] cobalt oxide (Co 3 O 4 ), [ 4 ] nickel oxide (NiO), [ 5 ] and nickel hydroxide (Ni(OH) 2 ), [ 6 ] have been extensively studied as electrode materials in pseudocapacitors. Among them, MnO 2 has stood out due to its outstanding characteristics such as high theoretical specifi c capacitance (∼1,400 F g −1 ), natural abundance, and environmental friendliness. [ 7 ] However, the poor electrical conductivity of MnO 2 (∼10 −5 – 10 −6 S cm −1 ) is a limiting factor in achieving its theoretical specifi c capacitance. [ 7b , 8 ] One feasible

Asymmetric Supercapacitor Electrodes and Devices

The world is recently witnessing an explosive development of novel electronic and optoelectronic devices that demand more-reliable power sources that combine higher energy density and longer-term durability. Supercapacitors have become one of the most promising energy-storage systems, as they present multifold advantages of high power density, fast charging-discharging, and long cyclic stability. However, the intrinsically low energy density inherent to traditional supercapacitors severely limits their widespread applications, triggering researchers to explore new types of supercapacitors with improved performance. Asymmetric supercapacitors (ASCs) assembled using two dissimilar electrode materials offer a distinct advantage of wide operational voltage window, and thereby significantly enhance the energy density. Recent progress made in the field of ASCs is critically reviewed, with the main focus on an extensive survey of the materials developed for ASC electrodes, as well as covering the progress made in the fabrication of ASC devices over the last few decades. Current challenges and a future outlook of the field of ASCs are also discussed.

Flexible, sandwich-like Ag-nanowire/PEDOT:PSS-nanopillar/MnO2 high performance supercapacitors

We demonstrate the design and fabrication of a Ag/PEDOT:PSS/MnO2 layer by layer structure for high performance flexible supercapacitors (SCs). This is a unique design combining Ag-nanowires and PEDOT:PSS-nanopillars as current collectors in SCs. In this sandwich-like structure, electrons can be easily transferred through a networked structure of Ag-nanowires to PEDOT:PSS-nanopillars and finally to the MnO2 layer and vice versa. This scheme provides excellent specific capacitances of 862 F g−1 (based on MnO2) at a current density of 2.5 A g−1 and robust long-term cycling stability. Moreover, SCs fabricated based on this structure exhibit exceptional flexibility and bendability (less than 2% loss in specific capacitance even after 100 bends) and high energy and power densities. All wet processing methods of fabrication along with superior performance make these SCs very attractive for the next generation flexible energy storage systems.

Modification of symmetrically substituted phthalocyanines using click chemistry: Phthalocyanine nanostructures by nanoimprint lithography

Phthalocyanines (Pcs) are commonly applied to advanced technologies such as optical limiting, photodynamic therapy (PDT), organic field-effect transistors (OFETs), and organic photovoltaic (OPV) devices, where they are used as the p-type layer. An approach to Pc structural diversity and the incorporation of a functional group that allows fabrication of solvent resistant Pc nanostructures formed by using a newly developed nanoimprint by melt processing (NIMP) technique, a variant of standard nanoimprint lithography (NIL), is reported. Copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC), a click chemistry reaction, serves as an approach to structural diversity in Pc macrocycles. We have prepared octaalkynyl Pc 1b and have modified this Pc using the CuAAC reaction to yield four Pc derivatives 5a-5d with different peripheral substituents on the macrocycle. One of these derivatives, 5c, has photo-cross-linkable cinnamate residues, and we have demonstrated the fabrication of robust cross-linked photopatterned and imprinted nanostructures from this material.

Coil‐Type Asymmetric Supercapacitor Electrical Cables

Cable-shaped supercapacitors (SCs) have recently aroused significant attention due to their attractive properties such as small size, lightweight, and bendability. Current cable-shaped SCs have symmetric device configuration. However, if an asymmetric design is used in cable-shaped supercapacitors, they would become more attractive due to broader cell operation voltages, which results in higher energy densities. Here, a novel coil-type asymmetric supercapacitor electrical cable (CASEC) is reported with enhanced cell operation voltage and extraordinary mechanical-electrochemical stability. The CASECs show excellent charge-discharge profiles, extraordinary rate capability (95.4%), high energy density (0.85 mWh cm(-3)), remarkable flexibility and bendability, and superior bending cycle stability (≈93.0% after 4000 cycles at different bending states). In addition, the CASECs not only exhibit the capability to store energy but also to transmit electricity simultaneously and independently. The integrated electrical conduction and storage capability of CASECS offer many potential applications in solar energy storage and electronic gadgets.