[Show abstract][Hide abstract] ABSTRACT: Layered composite samples of lithium-rich manganese oxide (Li1.2Mn0.6Ni0.2O2) are prepared by a reverse microemulsion route employing a soft polymer template and studied as a positive electrode material. The product samples possess dual porosity with distribution of pores at 3.5 and 60 nm. Pore volume and surface area decrease on increasing the temperature of preparation. Nevertheless, the electrochemical activity of the composite increases with an increase in temperature. The discharge capacity value of the samples prepared at 800 and 900 °C is about 240 mA h g−1 at a specific current of 25 mA g−1 with a good cycling stability. The composite sample heated at 900 °C possesses a high rate capability with a discharge capacity of 100 mA h g−1 at a specific current of 500 mA g−1. The high rate capability is attributed to porous nature of the composite sample.
Full-text · Article · Nov 2015 · New Journal of Chemistry
[Show abstract][Hide abstract] ABSTRACT: Electrodeposited Cu2O coatings with 111 out-of-plane orientation were found to have the lowest reversible discharge capacity as anodes for Li-ion cells. This is attributed to the low surface energy and the consequent high thermodynamic stability of the 111 crystal face of Cu2O. In contrast, the 200 oriented coating has a higher reversible discharge capacity, owing to its polar nature and high surface energy. The highest reversible discharge capacity was observed for unoriented coatings, emphasizing the critical role played by grain boundaries in the conversion electrodes. The morphology of crystallites in the electrodes recovered after cycling is different in the three cases, suggesting that the nature of reversible chemical conversion is guided by physical attributes of the precursor Cu2O crystallites.
No preview · Article · Nov 2015 · Journal of Solid State Electrochemistry
[Show abstract][Hide abstract] ABSTRACT: Energy storage devices based on sodium have been considered as an alternative to the traditional lithium based system because of its abundance in nature, cost effectiveness and low environmental impact. The synthesis, crystal and electronic properties, because of the importance of electronic conductivity in supercapacitors for high rate applications, have been discussed. The density of states of mixed sodium transition metal phosphate (maricite, NaMn1/3Co1/3Ni1/3PO4) has been determined with the ab initio generalized gradient approximation (GGA) + Hubbard term (U) method. Computed results for the mixed maricite are compared with the band gap of parent NaFePO4 and the electrochemical experimental results are in good agreement. Mixed sodium transition metal phosphate served as an active electrode material for hybrid supercapacitors. The hybrid device (maricite versus carbon) in non-aqueous electrolyte shows redox peaks in the cyclic voltammetry and asymmetric
profiles in the charge-discharge curves while exhibiting 40 F/g and these processes are found to be quasi-reversible. After long term cycling, the device exhibit excellent capacity retention (95%) and coulombic efficiency (92%) of the initial performance. The presence of carbon and nanocomposite morphology identified through X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) studies ensures the high rate capability while offering possibilities to develop new cathode material for sodium hybrid device.
Full-text · Article · Oct 2015 · Dalton Transactions
[Show abstract][Hide abstract] ABSTRACT: Poly(3,4-ethylenedioxythiophene) (PEDOT) supported PdRu catalysts with various Pd:Ru atomic ratios are prepared by one step electrodeposition method. The catalysts are characterised by several physicochemical techniques. The morphology depends on Pd:Ru ratio. The nanoflowers of Pd5Ru catalyst are deposited on PEDOT surface in an alloy form. Cyclic voltammetry experiments indicate that Ru improves the catalytic activity of Pd for glycerol oxidation significantly. However, the oxidation of glycerol is not observed on Ru-PEDOT/C electrode. Amongst all compositions, Pd5Ru nanoflowers on PEDOT exhibit the highest electrocatalytic activity and stability. Cyclic voltammetry and differential pulse voltammetry experiments are performed for the analysis of glycerol. Pd5Ru-PEDOT/C electrode is highly sensitive towards glycerol detection with sensitivity of 99.8 μA cm−2 μM−1 and low detection limit of 0.1 μM. Thus, electrochemically deposited nanoflowers Pd5Ru on PEDOT are efficient catalysts for direct glycerol oxidation as well as for analysis in alkaline media.
[Show abstract][Hide abstract] ABSTRACT: Iridium nanoparticles anchored reduced graphene oxide (Ir-RGO) is prepared by simultaneous reduction of graphene oxide and Ir3+ ions and its catalytic activity for oxygen electrode in Li-O2 cells is demonstrated. Ir particles of average size of 3.9 nm are uniformly distributed on the RGO sheets. Oxygen reduction reaction (ORR) is studied on Ir-RGO catalyst in non-aqueous electrolytes by using cyclic voltammetry and rotating disk electrode. Li-O2 cells with Ir-RGO as the oxygen bifunctional electrode catalyst are subjected to charge-discharge cycling at several current densities. A discharge capacity of 9529 mAh g-1 (11.36 mAh cm-2) is obtained initially at a current density of 0.5 mA cm-2 (393 mA g-1). There is a decrease in capacity on increasing current density. Although there is a decrease in capacity on repeated discharge-charge cycling initially, a stable capacity is observed for about 30 cycles. The results suggest that Ir-RGO is a useful catalyst for rechargeable Li-O2 cells.
Full-text · Article · Jun 2015 · New Journal of Chemistry
[Show abstract][Hide abstract] ABSTRACT: Porous flower-like α-Fe2O3 nanostructures have been synthesized by ethylene glycol mediated iron alkoxide as an intermediate and studied as an anode material of Li-ion battery. The iron alkoxide precursor is heated at different temperatures from 300 to 700 °C. The α-Fe2O3 samples possess porosity and high surface area. There is a decrease in pore volume as well as surface area by increasing the preparation temperature. The reversible cycling properties of the α-Fe2O3 nanostructures have been evaluated by cyclic voltammetry, galvanostatic charge discharge cycling, and galvanostatic intermittent titration measurements at ambient temperature. The initial discharge capacity values of 1063, 1168, 1183, 1152 and 968 mAh g−1 at a specific current of 50 mA g−1 are obtained for the samples prepared at 300, 400, 500, 600 and 700 °C, respectively. The samples prepared at 500 and 600 °C exhibit good cycling performance with high rate capability. The high rate capacity is attributed to porous nature of the materials. As the iron oxides are inexpensive and environmental friendly, the α-Fe2O3 has potential application as anode material for rechargeable Li batteries.
Full-text · Article · Jun 2015 · Electrochimica Acta
[Show abstract][Hide abstract] ABSTRACT: Reduced graphene oxide (RGO) is prepared by thermal exfoliation of graphite oxide in air. Symmetric RGO/RGO supercapacitors are constructed in a non-aqueous electrolyte and characterized. The values of energy density are 44 Wh kg −1 and 15 Wh kg −1 , respectively at 0.15 and 8.0 kW kg −1. The symmetric supercapacitor exhibits stable charge/discharge cycling tested up to 3000 cycles. The low-temperature thermal exfoliation approach is convenient for mass production of RGO at low cost and it can be used as electrode material for energy storage applications. Lithium ion batteries (LIBs) and supercapacitors (SCs) are promising energy storage devices for portable electronics, digital communications , hybrid electric vehicles, electric vehicles and renewable energy systems. 1–4 Electrical double layer capacitors (EDLCs) are the important electrochemical energy storage devices with long cycling stability in aqueous electrolytes. The specific capacitance measured in aqueous electrolytes is generally higher than in organic electrolyte. However, organic electrolytes are more attractive as they can withstand a higher operation voltage (up to 3 V) 5 than aqueous electrolyte (1.6 V for symmetric 6 and 2.0 V for asymmetric 7 supercapacitors). Compared with the batteries, the energy density of supercapacitors is often limited to less than 10 Wh kg −1. Efforts have been made to improve the energy density (E) of a supercapacitor by either improving its capacitance (C) or by increasing cell voltage (V) according to the equation, E = 0.5C V 2 .
Full-text · Article · May 2015 · ECS Electrochemistry Letters
[Show abstract][Hide abstract] ABSTRACT: A Li-rich layered-spinel material with a target composition Li1.17Ni0.25Mn1.08O3 (xLi[Li1/3Mn2/3]O2.(1-x)LiNi0.5Mn1.5O4, (x=0.5)) was synthesized by a self-combustion reaction (SCR), characterized by XRD, SEM, TEM, Raman spectroscopy and was studied as a cathode material for Li-ion batteries. Rietveld refinement results indicated the presence of monoclinic (Li[Li1/3Mn2/3]O2) (52 %), spinel (LiNi0.5Mn1.5O4) (39 %) and rhombohedral LiNiO2 (9 %). The electrochemical performance of this Li-rich integrated cathode material was tested at 30 ◦C and compared to that of high voltage LiNi0.5Mn1.5O4 spinel cathodes. Interestingly, the layered-spinel integrated cathode material exhibits a high specific capacity of about 200 mAh g-1 at C/10 rate as compared to 180 mAh g-1 for LiNi0.5Mn1.5O4 in the potential range of 2.4-4.9 V vs. Li anodes in half cells. The layered-spinel integrated cathodes exhibited 92 % capacity retention as compared to 82 % for LiNi0.5Mn1.5O4 spinel after 80 cycles at 30 ◦C. Also, the integrated cathode material can exhibit 105 mAh g-1 at 2C rate as compared to 78 mAh g-1 for LiNi0.5Mn1.5O4. Thus, the presence of the monoclinic phase in the composite structure helps to stabilize the spinel structure when high specific capacity is required and the electrodes have to work within a wide potential window. Consequently, the Li1.17Ni0.25Mn1.08O3 composite material described herein can be considered as an interesting cathode material for Li ion batteries.
[Show abstract][Hide abstract] ABSTRACT: In this study, thin films of cobalt oxide (Co3O4) have been grown by the metal-organic chemical vapor deposition (MOCVD) technique on stainless steel substrate at two preferred temperatures (450 °C and 500 °C), using cobalt acetylacetonate dihydrate as precursor. Spherical as well as columnar microstructures of Co3O4 have been observed under controlled growth conditions. Further investigations reveal these films are phase-pure, well crystallized and carbon-free. High-resolution TEM analysis confirms that each columnar structure is a continuous stack of minute crystals. Comparative study between these Co3O4 films grown at 450 °C and 500 °C has been carried out for their application as negative electrodes in Li-ion batteries. Our method of electrode fabrication leads to a coating of active material directly on current collector without any use of external additives. A high specific capacity of 1168 micro Ah cm-2 μm-1 has been measured reproducibly for the film deposited at 500°C with columnar morphology. Further, high rate capability is observed when cycled at different current densities. The Co3O4 electrode with columnar structure has a specific capacity 38% higher than the electrode with spherical microstructure (grown at 450°C). Impedance measurements on the Co3O4 electrode grown at 500 °C also carried out to study the kinetics of the electrode process.
No preview · Article · Feb 2015 · Journal of Power Sources
[Show abstract][Hide abstract] ABSTRACT: Presently Li/MnO2 is one of the widely used primary battery for a variety of applications. As the global resources for Na are plentiful in relation to those for Li, Na/MnO2 primary battery is expected to be an economical, viable alternate to Li/MnO2 system. But marginal inferior properties of Na/MnO2, which arise due to the differences in properties between Li and Na, are inevitable. In the present work, Na/MnO2 and Li/MnO2 laboratory scale primary cells in non-aqueous electrolytes are assembled and their electrochemical properties are studied in similar experimental conditions. The MnO2 used for these studies is prepared from KMnO4 and it is in amorphous state. The discharge behavior of Na/MnO2 cell is similar to that of Li/MnO2 cell, but with nominal voltage less by about 0.35 V, as expected. The specific capacity of amorphous MnO2 is 300 mAh g-1 in both Na/MnO2 and Li/MnO2 cells. On heating the as prepared amorphous MnO2 at temperature range 300-800°C, it converts to crystalline α-MnO2. The capacity of crystalline MnO2 is significantly less than the amorphous MnO2. The results suggest that Na/MnO2 is a viable, economical alternate to Li/MnO2 primary cell.
Full-text · Article · Feb 2015 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: The preparation of ZnO nanorod films decorated with cobalt-acetate (CoAc) electrocatalyst and its activity for photoelectrolysis of water have been demonstrated. The photochemically prepared CoAc catalyst is chemically and morphologically similar to the electrochemically prepared CoAc catalyst. The on-set potential of oxygen evolution reaction is lower on CoAc-ZnO photoanode in relation to bare ZnO photoanode. There is a three to four fold increase in photooxidation current of OER due to the presence of CoAc co-catalyst on ZnO. Thus, the photochemically prepared CoAc on ZnO is an alternative and efficient co-catalyst for photo electrochemical oxygen evolution reaction. The enhancement in photocatalytic activity of ZnO by the CoAc catalyst photochemically deposited from acetate buffer solution is greater than the widely reported cobalt-phosphate (CoPi) co-catalyst deposited from phosphate buffer electrolytes.
Full-text · Article · Feb 2015 · Journal of The Electrochemical Society
[Show abstract][Hide abstract] ABSTRACT: The partially exfoliated and reduced graphite oxide (PE-RGO) is prepared by low temperature thermal exfoliation of graphite oxide under air atmosphere. A symmetric carbon/carbon supercapacitor is studied in a Na2SO4 aqueous electrolyte. The discharge capacitance is 92 F g−1, when symmetric cell is cycled between the potential ranges from 0 to 1.6 V. This system demonstrates a stable charge/discharge cycle behavior up to 3000 cycles when the cell is operated at a voltage window of 1.6 V. The utilization ratio of potential window is 90% for this system is attributed to the more negative value of electrodes potential when the cell voltage is set to 0 V. The low-temperature exfoliation approach is convenient for mass production of graphenes at low cost and it can be used as electrode material for energy storage applications.
Full-text · Article · Dec 2014 · Solid State Communications
[Show abstract][Hide abstract] ABSTRACT: A porous layered composite of Li2MnO3 and LiMn0.35Ni0.55Fe0.1O2 (composition:Li1.2Mn0.54Ni0.22Fe0.04O2) is prepared by inverse microemulsion method and studied as a positive electrode material. The precursor is heated at several temperatures between 500 and 900 degrees C. The X-ray diffraction, scanning electron microscopy, and transmission electron microscopy studies suggested that well crystalline submicronsized particles are obtained. The product samples possess mesoporosity with broadly distributed pores around 10 similar to 50 nm diameter. Pore volume and surface area decrease by increasing the temperature of preparation. However, the electrochemical activity of the composite samples increases with an increase in temperature. The discharge capacity values of the samples prepared at 900 degrees C are about 186 mAh g(-1) at a specific current of 25 mA g(-1) with an excellent cycling stability. The composite sample also possesses high rate capability. The high rate capability is attributed to the porous nature of the material.
Full-text · Article · Oct 2014 · Electrochimica Acta
[Show abstract][Hide abstract] ABSTRACT: Porous α-Fe2O3 nanostructures have been synthesized by a simple sol–gel route. The α-Fe2O3 nanostructures are poorly crystalline and porous with BET surface area of 386 m2 g−1. The high discharge capacitance of α-Fe2O3 electrodes is 300 F g−1 when the electrodes are cycled in 0.5 M Na2SO3 at a current density of 1 A g−1. The capacitance retention after 1000 cycles is about 73% of the initial capacitance at a current density of 2 A g−1. The high discharge capacitance of α-Fe2O3 in comparison with the literature reports are attributed to high surface area and porosity of the iron oxide prepared in the present study. As the iron oxides are inexpensive, the capacity of α-Fe2O3 is expected to be of potential use for supercapacitor application.
[Show abstract][Hide abstract] ABSTRACT: Silver nanoparticles-anchored reduced graphene oxide (Ag-RGO) is prepared by simultaneous reduction of graphene oxide and Ag+ ions in an aqueous medium by ethylene glycol as the reducing agent. Ag particles of average size of 4.7 nm are uniformly distributed on the RGO sheets. Oxygen reduction reaction (ORR) is studied on Ag-RGO catalyst in both aqueous and non-aqueous electrolytes by using cyclic voltammetry and rotating disk electrode techniques. As the interest in non-aqueous electrolyte is to study the catalytic performance of Ag-RGO for rechargeable Li-O2 cells, these cells are assembled and characterized. Li-O2 cells with Ag-RGO as the oxygen electrode catalyst are subjected to charge-discharge cycling at several current densities. A discharge capacity of 11,950 mAh g-1 (11.29 mAh cm-2) is obtained initially at low a current density. Although there is a decrease in capacity on repeated discharge-charge cycling initially, a stable capacity is observed for about 30 cycles. The results indicate that Ag-RGO is a suitable catalyst for rechargeable Li-O2 cells.
Full-text · Article · Aug 2014 · Physical Chemistry Chemical Physics
[Show abstract][Hide abstract] ABSTRACT: Li-ion battery thin film battery TiN anode electrochemical performance a b s t r a c t TiN thin films with (200) fibre texture are deposited on Cu substrate at room temperature using reactive magnetron sputtering. They exhibit a discharge capacity of 172 Ah cm −2 m −1 (300 mAh g −1) in a non-aqueous electrolyte containing a Li salt. There is a graded decrease in discharge capacity when cycled between 0.01 and 3.0 V. Electron microscopy investigations indicate significant changes in surface morphology of the cycled TiN electrodes in comparison with the as deposited TiN films. From XPS depth profile analysis, it is inferred that Li intercalated TiN films consist of lithium compounds, hydroxyl groups, titanium sub oxides and TiN. Lithium diffusivity and reactivity decrease with increase in depth and the major reaction with lithium takes place at film surface and grain boundaries.
Full-text · Article · May 2014 · Electrochimica Acta
[Show abstract][Hide abstract] ABSTRACT: The present paper describes the scheme used to fabricate completely sealed dye sensitized solar cell (DSC) and its stability analysis employing acetonitrile as the solvent for redox couple. Since acetonitrile is extremely volatile a perfect sealing is essential to prevent the leakage of electrolyte. The usual hot melt sealing is employed for edge sealing whereas hole sealing is carried out with tooth pick and a UV curable adhesive. The degradation in efficiency is found to be 20% for low efficiency cells whereas, for high efficiency cells it is found to be 45% after 45 days. The leakage of highly volatile acetonitrile through the edge and hole is mainly responsible for the reduction in the performance of the device. Hence a high temperature sealing method is proposed to fabricate stable cells.
[Show abstract][Hide abstract] ABSTRACT: Nanodendritic Pd electrodeposited on poly(3,4-ethylenedioxythiophene) (PEDOT) modified Pd nanodendrite electrodes has been studied for electroanalysis of As(iii) in 1 M HCl solution. The Pd nanodendrites are grown on a porous thin film of PEDOT by electrodeposition process. Pd-PEDOT/C electrodes are characterized by physicochemical and electrochemical studies. Cyclic voltammetry studies show that Pd-PEDOT/C electrodes exhibit greater electrocatalytic activity towards As(iii)/As(0) redox reaction than the Pd/C electrodes. Differential pulse anodic stripping voltammetry (DPASV) is performed for analysis of As(iii) ion at pH 1.0. The Pd-PEDOT/C electrode is highly sensitive towards As(iii) detection with sensitivity of 1482 μA cm(-2) μM(-1). A wide detection range up to 10 μM and low detection limit of 7 nM (0.52 ppb) are obtained with a pre-deposition time of 120 s under optimum conditions. High sensitivity and low detection limit obtained on Pd-PEDOT/C, for the first time in the literature, are attractive from a practical view point. Interference studies of Cu(ii) ions are investigated and it is observed that Cu(ii) ions do not interfere.