Hydrothermal syntheses of tungsten doped TiO 2 and TiO 2 /WO 3 composite using metal oxide precursors for charge storage applications

Synthesis of advanced functional materials through scalable processing routes using greener approaches is essential for process and product sustainability. In this article, syntheses of nanoparticles of titanium dioxide (TiO₂), tungsten trioxide (WO₃), WO₃-doped titanium dioxide (W-TiO₂) and TiO₂/WO₃ composite at hydrothermal conditions using corresponding metal oxide precursors are described. Electrochemical charge storage capabilities of the above materials are measured using cyclic voltammetry, charge-discharge cycling and electrochemical impedance spectroscopy in aqueous KOH electrolyte. The TiO₂ and the WO₃ nanoparticle showed a specific charge (Q) of ∼12 and ∼36 mA h g⁻¹ at a current density of 2 A g⁻¹ in 6 M KOH, respectively. The Q of TiO₂ increased upon W doping up to 25 mA h g−1 for 5 wt% W-TiO2 and the WO₃/TiO₂ composite showed the highest storage capability (Q ∼40 mA h g⁻¹). Changes in the charge storage capabilities of the doped and composite materials have been correlated to materials properties.Bhupender Pal acknowledges the Research & Innovation Department of Universiti Malaysia Pahang (http://ump.edu.my) for award of Postdoctoral Fellowship. This project is funded under Flagship Strategic Leap 3 of Universiti Malaysia Pahang (Grant Number # RDU 172201)

Large Scale Synthesis of Binary Composite Nanowires in the Mn2O3-SnO2 System with Improved Charge Storage Capabilities

Large scale production of electrochemical materials in non-conventional morphologies such as nanowires has been a challenging issue. Besides, functional materials for a given application do not often offer all properties required for ideal performance; therefore, a composite is the most sought remedy. In this paper, we report large scale production of a composite nanowire, viz. Mn2O3-SnO2, and their constituent binary nanowires by a large scale electrospinning pilot plant consisting of 100 needles. Electrochemical characterization of thus produced composite nanowires showed nearly threefold increase in the discharge capacity compared to their single component counterparts: Mn2O3-SnO2 ∼53 mA h g−1 (specific capacitance, CS ∼384 F g−1); Mn2O3 ∼18 mA h g−1 (CS ∼164 F g−1); and SnO2 ∼14 mA h g−1 (CS ∼128 F g−1) at 1 A g−1 in 6 M KOH. The EIS studies showed that the characteristic resistances and time of the composite electrode are appreciably lower than their constituents. Owing to the scalability of the synthesis processes and promising capacitive properties achieved would lead the composite material as a competitive low-cost and high-performance supercapacitor electrode

Pseudocapacitive charge storage in thin nanobelts

This article reports that extremely thin nanobelts (thickness ~ 10 nm) exhibit pseudocapacitive (PC) charge storage in the asymmetric supercapacitor (ASC) configuration, while show battery-type charge storage in their single electrodes. Two types of nanobelts, viz. NiO–Co3O4 hybrid and spinal-type NiCo2O4, developed by electrospinning technique are used in this work. The charge storage behaviour of the nanobelts is benchmarked against their binary metal oxide nanowires, i.e., NiO and Co3O4, as well as a hybrid of similar chemistry, CuO–Co3O4. The nanobelts have thickness of ~ 10 nm and width ~ 200 nm, whereas the nanowires have diameter of ~ 100 nm. Clear differences in charge storage behaviours are observed in NiO–Co3O4 hybrid nanobelts based ASCs compared to those fabricated using the other materials—the former showed capacitive behaviour whereas the others revealed battery-type discharge behaviour. Origin of pseudocapacitance in nanobelts based ASCs is shown to arise from their nanobelts morphology with thickness less than typical electron diffusion lengths (~ 20 nm). Among all the five type of devices fabricated, the NiO–Co3O4 hybrid ASCs exhibited the highest specific energy, specific power and cycling stability

Hydrothermal Synthesis of α-MnO2 Nanorods and its Electrochemical Characterization for Supercapacitor Applications

MnO2 is considered as a candid material for supercapacitor applications owing to its varied oxidation states, environmental friendliness and low cost. α-MnO2 nanorods is synthesized by a facile hydrothermal method and is characterized by X-ray Diffraction, Field Emission Scanning Electron Microscopy, gas adsorption studies, cyclic voltammetry, Galvanostatic charge-discharge studies and Electrochemical impedance spectroscopy. The α-MnO2 demonstrated a promising specific capacitance of ~310 F g-1 at a current density of 1 A g-1 with lower contact resistance in 3M LiO

Ceramic-polyaniline composites for asymmetric supercapacitors

Supercapacitors are power devices having lower energy storage capacities. Different materials are researched for increasing its energy density without decreasing its power density. Polymer nanocomposites are one of such materials researched intensively as electrode material for supercapacitor applications. Different conducting polymers such as polyaniline, polypyrrole, and polythiol were used in the synthesis of different carbon as well as ceramic polymer nanocomposites. Out of these conducting polymer nanocomposites, metal or ceramic-polyaniline (PANi) nanocomposites are researched for supercapacitor electrodes due to their higher energy density than its contributors. Herein, the utility, research progress, and the energy storage parameters of asymmetric supercapacitors employing ceramic/PANi composites as electrodes are detailed.</p

Improving The Symmetry Of Asymmetric Supercapacitors Using Battery-Type Positive Electrodes And Activated Carbon Negative Electrodes By Mass And Charge Balance

Asymmetric supercapacitors (ASCs) are routinely fabricated using battery-type electrode materials as a positive electrode and electrochemical double layer materials as a negative electrode; the mass-loading in the electrodes is determined by assuming both to be capacitive charge storage materials. This protocol is erroneous as the cyclic voltammograms and galvanostatic charge-discharge curves of the resulting devices showed dissimilarity in the stored charges of the two electrodes and battery-type behaviors, respectively. Herein, we show by employing two choices of battery-type electrodes as positive electrodes and commercial activated carbon as negative electrode in 3 M LiOH electrolyte that equal mass loading in both electrodes leads to supercapacitive charge storage. The positive electrode to negative electrode mass ratio is varied from 0.75 to 1.5 in a mass interval of 0.25 which includes a mass ratio of the conventional method. The electrochemical studies of the fabricated ASCs show that the charge storage capabilities depend on the electrode mass. Electrochemical impedance spectroscopy studies show that the equal mass ratio has low series and charge transfer resistances and wider frequency dispersion of capacitance

Multifunctional Multicomponent Nanowires for Energy Conversion and Storage

Composites of functional materials have long been synthesized for achieving enhanced physical and chemical properties. Composite properties are achieved through many methods such as physical mixing of its components, chemical methods such as core/shell, hierarchical structures, nanoparticle-decorated nanowires, carbon structured reinforced porous materials and so on. In this era of energy intensive electronics and automobiles, and simultaneously having alarm from global atmospheric changes, generating electrical energy from renewable sources and storing them for further use are of extreme importance. Onedimensional nanostructures such as nanowires, nanorods, and nanobelts offer many advantages in energy conversion and storage devices such as channeled electron transport, anisotropic charge assembly, improved surface to volume ratio and so on. Many materials have screened in the past for high performance in energy conversion and storage devices; however, achievements in one of the properties has always been at the expense of another. If the composite materials are synthesized as one-dimensional materials, many properties could be assembled in a single material architecture. We have synthesized materials of unique advantages in a single nanowire or nanobelts and evaluated their usefulness in energy conversion and storage devices. Many bottlenecks in energy conversion and storage devices have been overcome using this protocol, the lecture would detail these developments

Characterization of MgCo2O4 as an Electrode for High Performance Supercapacitors

Metal cobaltites have promising electrochemical properties for their application as an energy storage medium. In this paper, usefulness of MgCo2O4 as a supercapacitor electrode is demonstrated and compared its performance with two other cobaltites, MnCo2O4 and CuCo2O4. The materials are synthesized using molten salt method and characterized by X-ray diffraction, scanning electron microscopy, BET surface area, cyclic voltammetry, galvanostatic charge–discharge cycling, and electrochemical impedance spectroscopy techniques. The MgCo2O4 electrodes show superior charge storage properties in 3 M LiOH among a diverse choice of electrolytes. The MgCo2O4 show higher theoretical (∼3122 F/g) and practically achieved capacitance (∼320 F/g), larger coulombic efficiency, and cycling stability than the other two; therefore, it could be developed as a low-cost energy storage medium

One-Dimensional Assembly of Conductive and Capacitive Metal Oxide Electrodes for High-Performance Asymmetric Supercapacitors

A one-dimensional morphology comprising nanograins of two metal oxides, one with higher electrical conductivity (CuO) and the other with higher charge storability (Co3O4), is developed by electrospinning technique. The CuO–Co3O4 nanocomposite nanowires thus formed show high specific capacitance, high rate capability, and high cycling stability compared to their single-component nanowire counterparts when used as a supercapacitor electrode. Practical symmetric (SSCs) and asymmetric (ASCs) supercapacitors are fabricated using commercial activated carbon, CuO, Co3O4, and CuO–Co3O4 composite nanowires, and their properties are compared. A high energy density of ∼44 Wh kg–1 at a power density of 14 kW kg–1 is achieved in CuO–Co3O4 ASCs employing aqueous alkaline electrolytes, enabling them to store high energy at a faster rate. The current methodology of hybrid nanowires of various functional materials could be applied to extend the performance limit of diverse electrical and electrochemical devices

Pseudocapacitive Charge Storage in Single-Step-Synthesized CoO-MnO2-MnCo2O4 Hybrid Nanowires in Aqueous Alkaline Electrolytes

A new pseudocapacitive combination, viz. CoOMnO2−MnCo2O4 hybrid nanowires (HNWs), is synthesized using a facile single-step hydrothermal process, and its properties are benchmarked with conventional battery-type flower-shaped MnCo2O4 obtained by similar processing. The HNWs showed high electrical conductivity and specific capacitance ( Cs) (1650 Fg −1 or 184 mA h g −1 at 1 A g−1) with high capacity retention, whereas MnCo2O4 nanoflower electrode showed only one-third conductivity and one-half of its capacitance (872 F g−1 or 96 mA hg −1 at 1 A g−1) when used as a supercapacitor electrode in 6 MKOH electrolyte. The structure −property relationship of the materials is deeply investigated and reported herein. Using the HNWs as a pseudocapacitive electrode and commercial activated carbon as a supercapacitive electrode we achieved battery-like specific energy ( Es) and supercapacitor-like specific power ( Ps) in aqueous alkaline asymmetric supercapacitors (ASCs). The HNWs ASCs have shown high Es (90 Wh kg−1) (volumetric energy density Ev ≈ 0.52 Wh cm −3) with Ps up to ∼104 W kg −1 (volumetric power density Pv ≈ 5 W cm −3) in 6 M KOH electrolyte, allowing the device to store an order of magnitude more energy than conventional supercapacitors