Raj Kishore Sharma

Morphology Controlled Synthesis of Nanoporous Co3O4 Nanostructures and Their Charge Storage Characteristics in Supercapacitors

Cubic spinel Co3O4 nanoparticles with spherical (0D) and hexagonal platelet (2D) morphologies were synthesized using a simple solvothermal method by tuning the reaction time. XRD and HRTEM analyses revealed pure phase with growth of Co3O4 particles along [111] and [110] directions. UV-vis studies showed two clear optical absorption peaks corresponding to two optical band gaps in the range of 400-500 nm and 700-800 nm, respectively, related to the ligand to metal charge transfer events (O(2-) → Co(2+,3+)). Under the electrochemical study in two electrode assembly system (Co3O4/KOH/Co3O4) without adding any large area support or a conductive filler, the hexagonal platelet Co3O4 particles exhibited comparatively better characteristics with high specific capacitance (476 F g(-1)), energy density 42.3 Wh kg(-1) and power density 1.56 kW kg(-1) at current density of 0.5 Ag(-1), that suited for potential applications in supercapacitors. The observed better electrochemical properties of the nanoporous Co3O4 particles is attributed to the layered platelet structural arrangement of the hexagonal platelet and the presence of exceptionally high numbers of regularly ordered pores.

Ultrahigh Performance Supercapacitor from Lacey Reduced Graphene Oxide Nanoribbons

High performance lacey reduced graphene oxide nanoribbons (LRGONR) were chemically synthesized. Holes created during the LRGONR synthesis not only enhanced the electrolytic accessibility but destacked all the graphene layers through protrusion at edge planes and corrugation in individual graphene. LRGONR in a supercapacitor cell showed ultrahigh performance in terms of specific capacitance and capacity retention. Consistently in aqueous, nonaqueous, and ionic electrolytes, LRGONR symmetric supercapacitor exhibited exceptionally high energy/power density, typically 15.06 W h kg(-1)/807 W kg(-1) in aqueous at 1.7 A g(-1), 90 W h kg(-1)/2046.8 W kg(-1) in nonaqueous at 1.8 A g(-1), and 181.5 W h kg(-1)/2316.8 W kg(-1) in ionic electrolyte at ∼1.6 A g(-1).

Electrochemically deposited bismuth telluride thin films

Thin films ofbismuth telluride grown by electrochemical deposition technique on conducting glass and Mo sheet substrates, were characterized for their structural, morphological, optical and compositional analysis. These studies revealed polycrystalline anisotropic and layered structure ofthese films with different compositional stoichiometry. In the present work electrochemical deposition ofbismuth telluride thin films is studied as a dopant material in II–VI group absorber materials f or photovoltaic application since it has a narrow optical energy band gap of0.13 eV. In this deposition process different film growth parameters were optimized to get good quality ofcompositionally uniform bismuth telluride thin film. XRD analysis revealed a hexagonal symmetry with large c-axis lattice constants (Bi2Te3 ,B i 2þX Te3� X ). 2002 Elsevier Science B.V. All rights reserved.

Enhanced supercapacitor performance by incorporating nickel in manganese oxide

Nickel manganese mixed oxides (NiyMn1−yOx; 0 ≤ y ≤ 0.4) have been synthesized by in situ inclusion of nickel during the growth of manganese oxide (MnOx). The effect of nickel concentration in MnOx is investigated by cyclic voltammetry, current–voltage characteristics, scanning electron microscopy and N2 adsorption–desorption analysis. Variations in electronic conductivity and specific capacitance suggest that nickel concentration in the MnOx matrix significantly affects the supercapacitor electrode performance. At Ni/Mn ∼0.25, i.e. Ni0.2Mn0.8Ox, the material crystallizes into spinel NiMn2O4 as a prominent phase and exhibits a specific surface area (118 m2 g−1) with a granular morphology. Furthermore Ni0.2Mn0.8Ox exhibited low resistivity (2.07 × 104 Ohm cm) and consequently high specific capacitance ∼380 F g−1, endowing additional merits. The fabricated supercapacitor device (Ni0.2Mn0.8Ox//Ni0.2Mn0.8Ox) delivers 35 W h kg−1 energy density and 3.74 kW kg−1 power density with remarkably high capacitive retention ∼92% after 3000 galvanostatic charge–discharge cycles. These encouraging results show great potential in developing energy storage devices from manganese oxide based electrodes incorporating nickel in the lattice.

Nanoceria based electrochemical sensor for hydrogen peroxide detection

Oxidative stress is a condition when the concentration of free radicals and reactive molecular species rise above certain level in living systems. This condition not only perturbs the normal physiology of the system but also has been implicated in many diseases in humans and other animals. Hydrogen peroxide (H2O2) is known to be involved in induction of oxidative stress and has also been linked to a variety of ailments such as inflammation, rheumatoid arthritis, diabetes, and cancer in humans. It is one of the more stable reactive molecular species present in living systems. Because of its stability and links with various diseases, sensing the level of H2O2 can be of great help in diagnosing these diseases, thereby easing disease management and amelioration. Nanoceria is a potent candidate in free radical scavenging as well as sensing because of its unique redox properties. These properties have been exploited, in the reported work, to sense and quantify peroxide levels. Nanoceria has been synthesized using different capping agents: Hexamethylene-tetra-amine (HMTA) and fructose. CeO2-HMTA show rhombohedral and cubic 6.4 nm particles whereas CeO2-fructose are found to be spherical with average particle diameter size 5.8 nm. CeO2-HMTA, due to the better exposure of the active (200) and (220) planes relative to (111) plane, exhibits superior electrocatalytic activity toward H2O2 reduction. Amperometric responses were measured by increasing H2O2 concentration. The authors observed a sensitivity of 21.13 and 9.6 μA cm(-2) mM(-1) for CeO2-HMTA and CeO2-fructose, respectively. The response time of 4.8 and 6.5 s was observed for CeO2-HMTA and CeO2-fructose, respectively. The limit of detection is as low as 0.6 and 2.0 μM at S/N ratio 3 for CeO2-HMTA and CeO2-fructose, respectively. Ceria-HMTA was further tested for its antioxidant activity in an animal cell line in vitro and the results confirmed its activity.

Electricity from the silk cocoon membrane.

Silk cocoon membrane (SCM) is an insect engineered structure. We studied the electrical properties of mulberry (Bombyx mori) and non-mulberry (Tussar, Antheraea mylitta) SCM. When dry, SCM behaves like an insulator. On absorbing moisture, it generates electrical current, which is modulated by temperature. The current flowing across the SCM is possibly ionic and protonic in nature. We exploited the electrical properties of SCM to develop simple energy harvesting devices, which could operate low power electronic systems. Based on our findings, we propose that the temperature and humidity dependent electrical properties of the SCM could find applications in battery technology, bio-sensor, humidity sensor, steam engines and waste heat management.

Graphene nanoribbon wrapped cobalt manganite nanocubes for high performance all-solid-state flexible supercapacitors

Nanocubes of cobalt manganite, CoMn2O4, were grown in situ over graphene nanoribbons (GNRs) to form a CoMn2O4/GNR composite during hydrothermal processing. The proposed all-solid-state supercapacitor (SC), CoMn2O4/GNR//CoMn2O4/GNR, with a polymer gel electrolyte showed an excellent electrochemical performance. It can be reversibly cycled over a large potential range of 3 V, resulting from the synergism of the pseudocapacitive and electrical double layer capacitor (EDLC) materials. The pseudocapacitance arises from the binary redox couple of the different cations in CoMn2O4, which, in combination with the GNRs, endows a high performance and long term stability. The SC demonstrates a high energy density of 44.6 W h kg−1 and a power density of 11.3 kW kg−1 with a short diffusion coefficient (Da) of 1.02 × 10−7 cm2 s−1 and a relaxation time constant (τ) of 5.6 μs. It demonstrates ∼95% capacitive retention with a steady coulombic efficiency even after 12 000 charge/discharge cycles. Moreover, a steady performance of the cell with good capacitive behaviour, even in the harsh environment of different bending states, encourages its commercial use in portable electronics.

Development and properties of surfactant-free water-dispersible Cu2ZnSnS4 nanocrystals: a material for low-cost photovoltaics.

A simple, yet novel hydrothermal method has been developed to synthesize surfactant-free Cu2ZnSnS4 nanocrystal ink in water. The environmentally friendly, 2-4 nm ultrafine particles are stable in water for several weeks. Detailed X-ray diffraction (XRD) and high-resolution transmission electron microscopy revealed the formation of single-crystalline-kesterite-phase Cu2ZnSnS4. Elemental mapping by scanning electron microscopy/energy dispersive spectrometry corroborated the presence of all four elements in a stoichiometric ratio with minor sulfur deficiency. Finally, Raman spectroscopy ruled out the possible presence of impurities of ZnS, Cu2SnS3, SnS, SnS2, Cu(2-x)S, or Sn2S3, which often interfere with the XRD and optical spectra of Cu2ZnSnS4. X-ray photoelectron spectroscopic studies of the as-synthesized samples confirmed that the oxidation states of the four elements match those of the bulk sample. Optical absorption analyses of thin film and solution samples showed high absorption efficiency (>10(4) cm(-1)) across the visible and near-infrared spectral regions and a band gap E(g) of 1.75 eV for the as-synthesized sample. A non-ohmic asymmetric rectifying response was observed in the I-V measurement at room temperature. The nonlinearity was more pronounced for this p-type semiconductor when the resistance was measured against temperature in the range 180-400 K, which was detected in the hot-point probe measurement.

Growth of CdS and CdTe thin films for the fabrication of n-CdS/p-CdTe solar cell

Abstract Thin n-CdS and p-CdTe films were prepared by chemical spray pyrolysis and electrochemical deposition respectively. Excessive sulphur in the spray solution has promoted grain growth in CdS film. Microstructural features of CdS film with stoichiometric Cd:S concentration in the spray solution were more heterogeneous with grains, whereas film sprayed with excessive S show more uniformity, reduced grain boundary losses of current and improved shunt resistance through inhibition of leakage of current at narrow grain boundary or void site is expected and is indeed observed. Electrodeposition of CdTe films, beside the effect of the inherent process parameters, is also affected by crystalline and microstructural features of the underlying CdS. Nucleation of CdTe film is remarkably affected by CdS film spray deposited over glass substrate. Cell performance considerably depends upon the window layer CdS and the properties of sprayed CdS film depends considerably on the Cd:S ratio in the spray solution. A higher S content in the CdS film affects it optical transmission without changing the optical energy gap. This improves cell efficiency through reduction in CdS film resistivity. A typical increase in cell efficiency was found to increase from 8% to 10.5% using CdS film with Cd:S ratio as 1:1.1 and 1:1.3 respectively.

Solid-state, high-performance supercapacitor using graphene nanoribbons embedded with zinc manganite

The fabrication of flexible supercapacitor involves the challenging task of preparing flexible electrodes with a large capacitance and robust mechanical strength. We report here the formulation of a high-performance solid-state flexible supercapacitor using graphene nanoribbons embedded with zinc manganite (ZnMn2O4/GNR) as the electrode and a gel polymer membrane as the electrolyte. The in situ availability of the graphene oxide nanoribbons led to the uniform dispersion of ZnMn2O4 nanospheres (about 7 nm), resulting in enhanced transport of the electrolyte ions. The fabricated ZnMn2O4/GNR∥ZnMn2O4/GNR supercapacitor was optimized with a maximum operating cell potential of 2.7 V. It delivered an energy density of about 37 W h kg−1 and had a power density of about 30 kW kg−1 at 1.25 A g−1 with good cycling stability over 4000 cycles. The high diffusion coefficient and short relaxation time of 0.34 μs (at 75 °C) are indicators of its high performance and stability at increased temperature. The superior flexibility and durability of the supercapacitor cell are evidence of their performance stability over consecutive galvanostatic charge/discharge cycles under harsh conditions.