S. Selladurai

Controlled growth of spinel NiCo2O4 nanostructures on carbon cloth as a superior electrode for supercapacitors

In this study, the morphology conversion of bimetallic NiCo2O4 nanostructures on carbon fiber cloth (CFC) was achieved via a simple hydrothermal approach with different precursor salts. As expected, the surface morphology has been successfully driven by varying the precursor. Typical NiCo2O4 nanowall-networks and porous nanoflake microstructures have been grown when using the nitrate and chloride precursors respectively. As an advantage of their unique structural features, they have shown different electrochemical activity towards supercapacitor applications. The as-grown NiCo2O4 nanowall-network structure delivers a maximum capacitance of 1225 F g−1 at a high current density of 5 A g−1 and excellent durability. However, a limited specific capacitance of only 844 F g−1 at a current density of 1 A g−1 was achieved for NiCo2O4 nanoflakes. This variation in the electrochemical features such as specific capacitance, rate capability and cyclic stability is mainly due to their structural discrepancies which have been driven by the precursors during the growth process. From this investigation it can be concluded that precursors with different anions also greatly influence the growth kinetics of metal oxide nanostructures. In this case, we suggest that the directly grown NiCo2O4@CFC with the desired microstructure will be a potential electrode for next generation flexible supercapacitors.

Shape controlled synthesis of CeO2 nanostructures for high performance supercapacitor electrodes

We report CeO2 nanostructures with the desired shape synthesized via a simple hydrothermal approach without any specific structure directing agent for supercapacitor applications. Well-distributed hexagonal nanoplates and nanorods were designed with large exposed surfaces under controlled hydrothermal conditions. As an advantage of this favorable shape and structural features, both of these nanostructures exhibit large specific capacitance values and excellent rate capabilities. Unique carbon supported CeO2 nanorod microstructures have shown a high capacitance of 644 F g−1 at 0.5 A g−1. Furthermore, they can deliver up to 400 F g−1 at a high current density of 20 A g−1. This is the first report of a CeO2 nanostructure for use as a supercapacitor electrode with a high rate capability. The notable electrochemical performance can be attributed to its large exposed surface, reasonable electronic conductivity, and the carbon support which increases the electrode/electrolyte contact significantly. The observed specific capacitance values are much higher and comparable with the other transition metal oxide electrodes. The present study suggests that the shape controlled CeO2 nanostructure will be an alternative high performance electrode for next generation supercapacitors.

Ultra-fast rate capability of a symmetric supercapacitor with a hierarchical Co3O4 nanowire/nanoflower hybrid structure in non-aqueous electrolyte

A free standing Co3O4 nanowire/nanoflower hybrid structure on flexible carbon fibre cloth (CFC) was designed via a facile hydrothermal approach followed by thermal treatment in air. The Co3O4 hybrid structure on CFC showed interesting electrochemical performance in both alkaline and organic electrolytes when used as electrodes for symmetric supercapacitors. Compared to conventional alkaline electrolytes, the fabricated symmetric cell in organic electrolyte has delivered a high rate and cyclic performance. A supercapacitor made from this hierarchical hybrid architecture showed a maximum specific capacitance of 4.8 mF cm−2 at a constant density of 3 mA cm−2 in organic electrolyte. In terms of energy and power, the symmetric supercapacitor conveyed an energy density of 4.2 mW h cm−3 with a power density of 1260 mW cm−3. Also, the device exhibited reasonable tolerance for mechanical deformation under bended conditions demonstrating the flexibility of the materials. The impressive electrochemical activity is mainly attributed to their high surface area (60.3 m2 g−1) resulting from their nano/mesoporous structure; reasonable electrical conductivity resulted from binder-free and intimate metal oxide/substrate integration and superior flexibility of the carbon fibre cloth. Thereby, it was concluded that the direct growth of the Co3O4 nanostructure on CFC is a promising electrode for the advanced flexible energy storage devices regardless of the electrolyte.

A 1-D/2-D hybrid nanostructured manganese cobaltite–graphene nanocomposite for electrochemical energy storage

A unique 1-D/2-D hybrid nanostructured manganese cobaltite–graphene nanocomposite (GMC) was synthesized by a facile hydrothermal method. Successful composite formation was determined from a structural study like XRD and chemical analyses like FTIR and XPS. FESEM and TEM observations of the manganese cobaltite compound reveal the flower like architecture formed by the clusters of MnCo2O4.5 nanowires. By graphene incorporation a unique hybrid 1-D/2-D nanostructure was developed in the composite material. BET surface area measurement reveals the extremely high surface area of the composite material owing to its distinct morphology. CV measurements reveal the excellent redox reactivity of the prepared electrode materials. GMC exhibited a high specific capacitance of 890 F g−1 which upon activation over cycling increases to 934 F g−1. MnCo2O4.5 decorated graphene sheets in the composite provide high interfacial sites for the redox process, exceptional electrical support and mechanical strength during cycling. The manganese cobaltite–graphene composite was able to retain 95% of its original capacitance at the end of 2000 cycles. The small solution resistance value of 1.21 Ω illustrates the superior conductivity of the composite material. A symmetrical cell fabricated using the GMC electrode material exhibited a maximum specific capacitance of 189 F g−1 at 5 mV s−1 scan rate. Fast reaction kinetics displayed by the cell were due to the charge transfer speedway provided by the graphene sheets. The superior performance of the hybrid composite makes it a potential candidate for supercapacitor applications.

Conductivity studies on PEO:NaClO3 electrolyte system with different plasticizers

A new ion conducting solid polymer electrolyte thin film based on Polyethylene oxide (PEO) with NaClO3 salt is prepared by solution-casting method. The solvation of salt with PEO has been confirmed by X-ray diffraction and IR spectral studies. Plasticizer effects were studied in PEO:NaClO3 system by using low molecular weight polyethylene glycol (PEG), dimethyl formamide (DMF) and propylene carbonate(PC). AC conductivity in the temperature range (308–378 K) was measured to evaluate the conductivity of the polymer electrolytes. From the conductivity data, it was found that the conductivity value of pure PEO increases 102–104 order of magnitude with the addition of salts as well as plasticizers. From the transference number experiments, it was confirmed that the charge transport in these electrolyte is mainly due to the ions (tion≈0.94). Finally, the conductivity value of all PEO: NaClO3 systems were compared.

Ionic conductivity and battery characteristic studies on PEO+NaClO3 polymer electrolyte

Solid polymer electrolyte films based on poly (ethylene oxide) PEO complexed with NaClO3 have been prepared by a solution-cast technique. The solvation of Na+ ion with PEO is confirmed by XRD and IR studies. Measurements of the a.c. conductivity in the temperature range 308 – 378 K and the transference numbers have been carried out to investigate the charge transport in this polymer electrolyte system. Transport number data show that the charge transport in this polymer electrolyte system is predominantly due to ions. The highest conductivity (2.12.10−4 S/cm) has been observed for the 70:30 composition. Using the polymer electrolyte solid state electrochemical cells have been fabricated. The various cell parameters are evaluated and reported.

A new type of electrochemical cell based on the configuration NaI |PEG| I2

Different operating conditions of a new electrochemical cell based on sodium iodide and polyethylene glycol (PEG) polymer as separator as well as conducting electrolyte is reported. Five types of cells were fabricated using pure NaI, PC+NaI, water+NaI dil. HCl+NaI and dil. H2SO4+NaI in the cell configuration NaI |PEG| I2 and NaI |PEG|s I2+C. Their discharge characteristics were studied at room temperature (33 °C). From the cell parameters, it is found that the open circuit voltage ranges from 648 mV to 1023 mV and the short circuit current ranges from 29 µA to 4.8 mA.

Synthesis and studies of new plasticized PVP: NaClO3 electrolyte system for battery applications

A new thin film sodium ion conducting plasticized polymer electrolyte based on poly(vinyl pyrrolidone) (PVP) complexed with NaClO3 salt systems was prepared by the solution-cast method. The interaction of NaClO3 salt with PVP was confirmed by Infrared (IR) study. Charge transport of these polymer electrolytes is due to ions, which was confirmed by Wagner’s polarization method. From the conductivity measurements, the highest conductivity value 6.71×10−5 S/cm was observed for the composition PVP:PEG:NaClO3(30:60:10) at room temperature 35 °C. The redox behaviour and good reversibility of the plasiticized electrolytes are confirmed by electrochemical techniques. Electrochemical cell studies of these polymer electrolytes were analyzed from their discharge characteristics. The open-circuit voltage (OCV) and short-circuit current (SCC) were found to in the range of 2.52 V to 2.36 V and 760 μA to 1040 μA, respectively.

Novel synthesis of highly porous spinel cobaltite (NiCo2O4) electrode material for supercapacitor applications

High performing porous nickel cobaltite (NiCo2O4) nanomaterial is prepared using novel cost effective auto combustion technique. Physical characterization reveals the formation of nickel rich spinel cobaltitie with average crystallite size of 17 nm. Electrochemical evaluation of the sample is carried using cyclic voltammetry (CV), chronopotentiometry (CP) and AC impedance techniques. The Pseudocapacitive nature of the material is observed from CV and CP studies exhibiting a high specific capacitance of 772 Fg−1 at a current density of 1 Ag−1. The low resistive behavior of the material is seen from the impedance spectra, projecting nickel cobaltite as promising material for supercapcitor applications.

Synthesis, structure and electrochemistry of LiMn2-yCry/2Cuy/2O4 (0.0 ≤ y ≤ 0.5) prepared by wet chemistry

Abstract The LiMn2O4 co-doped with copper and chromium forming LiMn2−yCry/2Cuy/2O4 spinel phases have been synthesized by wet chemistry technique using an aqueous solution of metal acetates and dicarboxylic acid (succinic acid) as a complexing agent. The structural properties of the synthesized products have been investigated by X-ray powder diffraction, Raman scattering, and Fourier-transform infrared spectroscopy. To improve the rechargeable capacity of Li//LiMn2−yCry/2Cuy/2O4 cells, the electrochemical features of LiMn2−yCry/2Cuy/2O4 compounds have been evaluated as positive electrode materials. The structural properties of these oxides are very similar to LiMn2O4, their electrochemical performances show that the capacity is maintained 95% of the initial value at the 36th cycle for y=0.1, this being explained by the change of Mn3+/Mn4+ ratio in doped phases.