Modification of Capacitive Charge Storage of TiO2 with Nickel Doping

For practical deployment of supercapacitors characterized by high energy density, power density and long cycle life, they must be realized using low cost and environmentally benign materials. Titanium dioxide (TiO2) is largely abundant in the earth's crust; however, they show inferior supercapacitive electrochemical properties in most electrolytes for practical deployment. In this paper, we show that nickel doped TiO2 (Ni:TiO2) nanowires developed by electrospinning showed five times larger capacitance (∼200 F g−1) than the undoped analogue (∼40 F g−1). Electrochemical measurements show that the Ni:TiO2 nanowires have 100% coulombic efficiency. The electrodes showed no appreciable capacitance degradation for over 5000 cycles. The superior charge storage capability of the Ni:TiO2 could be due to its high electrical conductivity that resulted in five orders of magnitude higher ion diffusion as determined by cyclic voltammetry and electrochemical impedance spectroscopy measurements

Development of nanocomposite nanowires by electrospinning as a supercapacitor electrode with high energy density, power density and rate capability

Deployment of renewable energy requires, in addition to efficient energy conversion devices, electrochemical materials capable of storing a large amount of electrical energy as well as delivering it at a high rate. Electrochemical capacitors represent a class of energy storage devices; thus optimizing the working electrodes for them is the key to achieving high energy (ES) and power densities (PS). However, ES and PS are not united in the existing devices. High electrochemical reversibility, multiple oxidation states, high surface area and high electrical conductivity are requirements for high ES and PS in supercapacitor electrodes. Most materials offering high theoretical capacitance owing to its multiple oxidation states have lesser electrical conductivity; therefore, it is hypothesized that the electrical conductivity plays a dominant role in combining ES and PS in a single device. One-dimensional (1D) nanowires show improved charge transport properties compared to their nanoparticle analogue; therefore, they are expected to deliver simultaneously ES and PS in a single device. Studies show that the ceramic electrode materials exhibits diverse range of capacitances and conductivities than other choice of materials; therefore, the target device could be achieved using ceramic electrodes. Three typical materials with nanowire morphology are chosen for this purpose, viz. copper oxide (CuO), nickel oxide (NiO), and cobalt oxide (Co3O4). Among them NiO and Co3O4 show larger theoretical capacitance estimated at 2570 and 3560 Fg-1 respectively, compared to CuO (1800 Fg-1); the later has larger electrical conductivity. Synthesizing a composite is one of the methods to combine the functions of different materials; therefore, CuO+NiO and CuO+Co3O4 composites are the target materials. These materials were synthesized as 1D nanowires using an aqueous polymeric solution based electrospinning process and their structural properties by X-ray and electron diffraction were studied, high resolution transmission electron microscopy; morphological properties by scanning and transmission electron microscopy; and electrochemical properties by cyclic voltammetry, galvanostatic charge discharge cycling, and electrochemical impedance spectroscopy. The electrochemical studies showed that CuO, NiO and Co3O4 achieve a specific capacitance (CS) nearly 30% of its theoretical value, but with low rate capability. The studies showed higher rate capability, lower equivalent series and charge transfer resistances in NiO + CuO and Co3O4+CuO composites than those of their single components. Asymmetric supercapacitor (ASC) using ceramic nanowire anode and commercially available activated carbon cathode were fabricated and their charge storage performance was compared with a symmetric supercapacitor fabricated using activated carbon at both electrodes. The ASC showed seven times higher specific capacitance and ES compared to the symmetric device. The PS decreased with ES for devices employed single component ceramic nanowires. However, ES remained practically same for increased PS when their composite mixture was used as working electrode. An ES of ~52.6 Whkg-1 with PS of ~14000 Wkg-1 is delivered by Co3O4+CuO based device which appear to be the best ever achieved in supercapacitor charge storage mod

High Performance Flower Shape Manganese Oxide For Asymmetric Supercapacitor Device

A flower shaped manganese oxide have been synthesized using simple and low temperature procedure. Subsequently, an asymmetric supercapacitor is fabricated using manganese oxide and activated carbon as positive and negative electrode in aqueous electrolyte. The supercapacitor was measured at open windows 2.0 V showing energy density of 25.79 Wh/kg at power density of 100 W/kg. The supercapacitor stability was tested at 3 A/g and showing specific capacitance retention of 95% after 850 cycle

High Performance Asymmetric Supercapacitors Using Electrospun Copper Oxide Nanowires Anode

We have fabricated, for the first time, an asymmetric supercapacitor (ASC) employing pseudocapacitive copper oxide (CuO) as anode and electrochemical double layer capacitive commercial activated carbon (AC) as cathode. The CuO is in the form of nanowires of diameter ∼30–50 nm developed using an aqueous polymeric solution based electrospinning process. The ASC showed larger voltage window (V ∼ 1.6 V) and specific capacitance (CS ∼ 83 Fg−1) than a control symmetric electrochemical double layer capacitor (EDLC) (V ∼ 1.4 V; CS ∼ 33 Fg−1) fabricated using the AC. The ASC delivered specific energy densities (ES) of 29.5, 23.5, 19.2 and 16.4 W h kg−1 at specific power densities (PS) 800, 1500, 4000 and 8400 W kg−1, respectively. The performance of ASC is much superior to the control EDLC, which delivered ES of 11, 10 and 8.8 W h kg−1 at PS 800, 1600 and 3900 W kg−1, respectively. Owing to the larger abundance of copper in the earth’s crust and promising charge storage properties achieved herewith, the present ASC could be developed as a commercial electrical energy storage device

Improved Supercapacitive Charge Storage in Electrospun Niobium Doped Titania Nanowires

Supercapacitors are emerging as a desirable energy storage medium in view of their order of magnitude higher power density than batteries and energy density than electronic capacitors. One of the key issues in the development of a suitable electrode material for supercapacitors is that materials showing large specific capacitance are poorly abundant. In this paper, we show that niobium doped titanium dioxide (Nb:TiO2) nanowires developed by electrospinning have an order of magnitude higher capacitance (~280 Fg-1) than pristine TiO2 (~40 Fg-1) or zirconium doped TiO2 (~30 Fg-1). The cyclic voltammetry and charge discharge cycling experiments show that the Nb:TiO2¬ nanowires have 100% coulombic efficiency and could be operated over 5000 cycles without any appreciable capacitance degradation. The superior charge storage capability of the Nb:TiO2 is assigned to its high electrical conductivity as determined by electrochemical impedance spectroscopy. A practical supercapacitor is fabricated in asymmetric configuration using the Nb:TiO2 as anode and activated carbon as cathode. The device delivered energy densities of 16.3, 11.4 and 5.6 Whkg-1 at power densities of 770, 1310, and 1900 Wkg-1, respectively. These values are much superior than a control device fabricated using activated carbon as its both electrodes

Doubling of Electrochemical Parameters via the Pre-intercalation of Na+ in Layered MnO2 Nanoflakes Compared to a-MnO2 Nanorods

The pre-intercalation of Na+ ions in layered birnessite-MnO2 is shown to have a dramatic influence on its electrochemical properties. Electrochemical studies showed the doubling of the specific capacitance and energy density in the layered Na–MnO2 nanoflakes compared to the MnO2 nanorods

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

Electrochemical Properties of Carbon from Oil Palm Kernel Shell for High Performance Supercapacitors

Electrochemical properties of activated carbon (AC) derived from oil palm kernel shell (PKS) are evaluated and compared with other biomass derived AC for fabricating high performance electrochemical double layer capacitors (EDLC). Cleaned PKS are carbonized by pyrolysis and subsequently activated by physical and chemical methods. The chemically AC show a wider pore distribution (1.49.3 nm) whereas the physically activated one has uniform pores (1.5 nm). The electrochemical properties of the two types of AC are evaluated using cyclic voltammetry (CV), charge–discharge cycling (CDC) and electrochemical impedance spectroscopy (EIS) in three-electrode configuration. High specific capacitance (CS) (210 F g-1 in 1 M KOH electrolyte at 0.5 A g-1) is obtained for chemically AC whereas the CS for the physically AC is 50% lower (123 F g-1). Galvanostatic CDC tests show that the electrodes maintained ~ 9597% of CS after 1000 cycles. The EIS revealed that the PKS AC has low series resistance (< 0.6 ) and relaxation time (~0.69 s) which would therefore offers high power density in the EDLC devices

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.This work is supported by Grants RDU 1503100 and GRS 150328 of Universiti Malaysia Pahang (http://ump.edu.my)