G. Ranga Rao

Microwave-Mediated Synthesis for Improved Morphology and Pseudocapacitance Performance of Nickel Oxide

Synthetic methods greatly control the structural and functional characteristics of the materials. In this article, porous NiO samples were prepared in conventional-reflux and microwave assisted heating method under homogeneous precipitation conditions. The NiO samples synthesized in conventional reflux method showed flakelike morphology, whereas the sample synthesized in microwave methods showed hierarchical porous ball like surface morphology with uniform ripple-shaped pores. The NiO samples characterized using BET method were found to bear characteristic meso- and macroporosity due to differently crystallized Ni(OH)(2) precursors under various heating conditions. Thermogravimety analysis showed morphology dependent decomposition of Ni(OH)(2) precursors. The microwave synthesized porous NiO sample with unique morphology and pore size distribution showed significantly improved charge storage and electrochemical stability than the flaky NiO sample synthesized by employing conventional reflux method. The cyclic voltammetry measurements on microwave synthesized NiO sample showed considerably high capacitance and better electrochemical reversibility. The charge-discharge measurements made at a discharge current of 2 A/g showed higher rate specific capacitance (370 F/g) for the NiO sample synthesized by microwave method than the sample synthesized by reflux method (101 F/g). The impedance study illustrates lower electronic and ionic resistance of rippled-shaped porous NiO due to its superior surface properties for enhanced electrode-electrolyte contact during the Faradaic redox reactions. It has been further established from the Ragone plot that the microwave synthesized NiO sample shows higher energy and power densities than the reflux synthesized NiO sample. Broadly, this study reveals that microwave-mediated synthesis approach is significantly a better strategy for the synthesis of porous NiO suitable to electrochemical supercapacitor applications.

Archetypal sandwich-structured CuO for high performance non-enzymatic sensing of glucose

In the quest to enhance the selectivity and sensitivity of novel structured metal oxides for electrochemical non-enzymatic sensing of glucose, we report here a green synthesis of unique sandwich-structured CuO on a large scale under microwave mediated homogeneous precipitation conditions. The physicochemical studies carried out by XRD and BET methods show that the monoclinic CuO formed via thermal decomposition of Cu(2)(OH)(2)CO(3) possesses monomodal channel-type pores with largely improved surface area (~43 m(2) g(-1)) and pore volume (0.163 cm(3) g(-1)). The fascinating surface morphology and pore structure of CuO is formulated due to homogeneous crystallization and microwave induced self assembly during synthesis. The cyclic voltammetry and chronoamperometry studies show diffusion controlled glucose oxidation at ~0.6 V (vs. Ag/AgCl) with extremely high sensitivity of 5342.8 μA mM(-1) cm(-2) and respective detection limit and response time of ~1 μM and ~0.7 s, under a wide dynamic concentration range of glucose. The chronoamperometry measurements demonstrate that the sensitivity of CuO to glucose is unaffected by the absence of dissolved oxygen and presence of poisoning chloride ions in the reaction medium, which essentially implies high poison resistance activity of the sandwich-structured CuO. The sandwich-structured CuO also shows insignificant interference/significant selectivity to glucose, even in the presence of high concentrations of other sugars as well as reducing species. In addition, the sandwich-structured CuO shows excellent reproducibility (relative standard deviation of ~2.4% over ten identically fabricated electrodes) and outstanding long term stability (only ~1.3% loss in sensitivity over a period of one month) during non-enzymatic electrochemical sensing of glucose. The unique microstructure and suitable channel-type pore architecture provide structural stability and maximum accessible electroactive surface for unimpeded mobility of glucose as well as the product molecules, which result in the excellent sensitivity and selectivity of sandwich-structured CuO for glucose under non-enzymatic milieu.

Synthesis of mesoporous NiCo2O4–rGO by a solvothermal method for charge storage applications

The spinel NiCo2O4 material has received considerable attention as an excellent supercapacitor material. In this study, we report a facile and cost-effective solvothermal method for the synthesis of mesoporous NiCo2O4 anchored on reduced graphene oxide (rGO). The electrochemical activity of the NiCo2O4–rGO and pristine NiCo2O4 materials were evaluated by cyclic voltammetry (CV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The NiCo2O4–rGO composite electrode shows a high specific capacitance value of 870 F g−1 at a current density of 2 A g−1 and it retains 600 F g−1 capacitance even at a high current density of 20 A g−1. Pristine NiCo2O4 shows a poor capacitance value of 315 F g−1 at 2 A g−1 and it retains only 191 F g−1 at 10 A g−1. Furthermore, the NiCo2O4–rGO nanocomposite shows an excellent cyclic performance with 90% capacitance retention even after 5000 charge–discharge cycles at a high current density of 4 A g−1, whereas a pristine NiCo2O4 electrode shows only 45% capacitance retention. The high specific capacitance, remarkable rate capability and excellent cycling performance offered by the NiCo2O4–rGO composite is attributed to the high surface area and high conductivity. In addition, rGO is believed to shorten the diffusion, migration paths for electrolyte ions and an easy access for electrolyte ions into redox centers.

In situ fabrication of graphene decorated microstructured globe artichokes of partial molar nickel cobaltite anchored on a Ni foam as a high-performance supercapacitor electrode

By taking advantage of the splendid properties of graphene (electrical conductivity) and transition metal oxides (pseudocapacitance nature), we have in situ fabricated novel microstructured globe artichokes of a rGO/Ni0.3Co2.7O4 composite on a nickel foam through a simple surfactant free hydrothermal method followed by calcination process. The globe artichoke flower-like morphology is constructed by hundreds of self-assembled micropetals interconnected with several layers and circles at the base to form microspheres of uniform dimension. The as-obtained morphology of the microstructured globe artichokes enhanced the stability and electrochemical performance of the hybrid electrode due to of its unique structure. Therefore, the synergetic effects and interconnected structure of the thus made binder free rGO/Ni0.3Co2.7O4 hybrid electrode allows better charge transport and exhibits superb specific capacitance and areal capacitance of 1624 F g−1 and 2.37 F cm−2 at a current density of 2 A g−1. Moreover, the specific capacitance increases from 1088 F g−1 to 1728 F g−1 at the end of 7000 cycles, which indicates that the material becomes active with cycling. Furthermore, when the power density increased by 16 times i.e. from 0.5 to 8 kW kg−1 the energy density sinks to 40 from 56.39 W h kg−1 (i.e., 29% reduction only), suggesting a remarkable electrochemical performance for supercapacitor applications.

Influence of Synthesis Conditions and Cerium Incorporation on the Properties of Zr-Pillared Clays

Zr-pillared clays were prepared from ZrOCl2 pillaring solutions by adopting different preparative conditions. Ce3+ ions are introduced to Zr-pillared clays by co-intercalation method. The resulting samples were characterized by XRD, TGA, N2 sorption and UV-VIS-Diffuse reflectance spectroscopy techniques. Basal spacings in the range of 18–21 Å were observed depending upon the preparative condition. TG analysis shows three weight loss regions corresponding to removal of various types of water molecules. All pillared clays show Type-I sorption isotherm typical of microporous materials. Pillaring under refluxing condition is found to have beneficial effect on the surface area and pore volume of the Zr-pillared clay. The chemical environment and location of Ce3+ ions is studied by UV-VIS-DRS. The Ce3+ ions are found to be present in the micropores of the Zr-pillared clays. However heat treatment at higher temperature may result in peripheral interaction between Ce3+ ions and Zr-pillars. Catalytic activity of these pillared clays was evaluated for cyclohexanol dehydration which correlates well with the Brønsted acidity of these materials. The Zr-Pillared clay containing Ce3+ ions show good catalytic activity and stability with reaction time which has been ascribed to the stabilazition of the Brønsted acidic centers.

Charge storage, electrocatalytic and sensing activities of nest-like nanostructured Co3O4

We synthesized nanostructured Co3O4 samples using anionic (SDS), cationic (CTAB) and nonionic (Triton X-100) surfactant molecules in hydrothermal conditions and subsequent calcination. This approach facilitates the synthesis of porous Co3O4 material with bundle-like-sheet, nest-like and flake-like morphologies with specific surface areas in the range of 50-77m2g-1. Among these materials, the nest-like nanostructured Co3O4 material has unique pore architecture, larger pore volume, low solution and charge transfer resistance, and found to be an active material for charge storage, electrocatalytic and sensing applications. The specific capacitance value of the nest-like Co3O4 is 404Fg-1 at a current density of 2Ag-1 with 80% specific capacitance retention. The electrocatalytic oxidation of methanol occurs at lower onset potential on this material with good electrochemical stability. It has good sensing ability for glucose with high sensitivity of 929μAcm-2mM-1, fast response time of ∼0.5s and detection limit as low as ∼1μM. These results show that the nest-like nanostructured Co3O4 material is a versatile candidate for various applications.

Vanadium pentoxide nanochains for high-performance electrochemical supercapacitors

We have synthesized unique hierarchical one dimensional (1D) nanochains of V2O5 by employing simple hydrothermal method using cetyltrimethylammonium bromide (CTAB) as a soft template. The electrochemical performance of resulting V2O5 electrode materials was evaluated by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy techniques. The V2O5 nanochains (V2O5-ctab) show maximum specific capacitance of 631 F g(-1) at a current density of 0.5 A g(-1) and retain 300 F g(-1) even at high current density of 15 A g(-1). In addition the V2O5 nanochains show good cyclic stability with 75% capacitance retention after 1200 charge-discharge cycles. The order of specific capacitance is commercial bulk-V2O5 (160 F g(-1))<agglomerated V2O5 particles (395 F g(-1))<V2O5 nanochains (631 F g(-1)). The interconnected nanochain-like morphology and high specific surface area are the main factors which contribute to higher electrochemical performance to V2O5 nanochains and promote facile exchange of Li(+) ions during the charge-discharge processes.

PWA/montmorillonite K10 catalyst for synthesis of coumarins under solvent-free conditions

Abstract12-Tungstophosphoric acid supported on montmorillonite K10 (PWA/mont-K10) catalysed Pechmann condensation reaction was reported. The catalyst was characterized by XRD, FTIR, UV–Vis DRS, surface area and pore size analysis, TGA and acidity by DRIFTS using pyridine. The morphology of the catalyst was studied by SEM. The activity of mont-K10, mont-KSF,

In situ grown nano-architectures of Co3O4 on Ni-foam for charge storage application

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