Sulphur source-inspired self-grown polycrystalline and mesoporous nickel sulfide (Ni x S y ) superstructures with vertically aligned nanomorphologies viz. rods, flakes, buds, and petals, synthesized at elevated temperatures and moderate pressures by a facile one-pot hydrothermal method on a three-dimensional Ni foam demonstrate remarkable areal specific capacitances of 7152, 4835, and 2160 F cm −2 at current densities of 1, 2, and 5 mA cm −2 , respectively, with a cycling stability of 94% for a battery-type electrochemical supercapacitor when used as an electrode material in a supercapacitor. The Ni x S y //Bi 2 O 3 asymmetric supercapacitor assembly exhibits an energy density of 41 W h•kg −1 at a power density of 1399 W kg −1 for 1 A g −1 and was used in a three-cell series combination to operate a "GFHIM" display panel (our research institute name, Global Frontier R & D Center for Hybrid Interface Materials) composed of nearly 50 differently colored light-emitting diodes with high intensity in 1 M KOH water-alkali electrolyte. The electrochemical supercapacitor results obtained for the Ni x S y superstructures because of a combination of catalytically active amorphous and high mobility polycrystalline are highly comparable to those reported previously for salt-mediated and self-grown Ni x S y structures and morphologies.
Soft chemical synthesis is used to obtain a hydrangea-type bismuth molybdate (Bi 2 MoO 6 ) supercapattery electrode that demonstrates considerable energy/power density and cycling life. Structure and morphology studies, initially, reveal a phase-pure polycrystalline and hydrangea-type surface appearance for Bi 2 MoO 6 , which upon testing in an electrochemical energy storage system displays supercapattery behavior, a combination of a supercapacitor and a battery. From the power law, an applied-potential-dependent charge storage mechanism is established for the Bi 2 MoO 6 electrode material. A Trasatti plot evidences the presence of inner and outer surface charges. The hydrangea-type Bi 2 MoO 6 electrode demonstrates a specific capacitance of 485 F g –1 at 5 A g –1 and a stability of 82% over 5000 cycles. An assembled symmetric supercapattery with a Bi 2 MoO 6 //Bi 2 MoO 6 configuration demonstrates energy and power densities of 45.6 W h kg –1 and 989 W kg –1 , respectively. A demonstration elucidating the lighting up of three light-emitting diodes, connected in series, by the symmetric supercapattery signifies the practical potentiality of the as-synthesized hydrangea-type Bi 2 MoO 6 electrode in energy storage devices.
We report water-splitting application of chemically stable self-grown nickel sulfide (Ni x S y ) electrocatalysts of different nanostructures including rods, flakes, buds, petals, etc., synthesized by a hydrothermal method on a three-dimensional Ni foam (NiF) in the presence of different sulfur-ion precursors, e.g., thioacetamide, sodium thiosulfate, thiourea, and sodium sulfide. The S 2– ions are produced after decomposition from respective sulfur precursors, which, in general, react with oxidized Ni 2+ ions from the NiF at optimized temperatures and pressures, forming the Ni x S y superstructures. These Ni x S y electrocatalysts are initially screened for their structure, morphology, phase purity, porosity, and binding energy by means of various sophisticated instrumentation technologies. The as-obtained Ni x S y electrocatalyst from sodium thiosulfate endows an overpotential of 200 mV. The oxygen evolution overpotential results of Ni x S y electrocatalysts are comparable or superior to those reported previously for other self-grown Ni x S y superstructure morphologies.
A low-temperature (90 °C) and directly grown anatase titanium dioxide (TiO2) nanocrystalline film using successive ionic layer adsorption and reaction (SILAR) for perovskite solar cell and gas sensor applications. TiO2 nanocrystalline electron transfer layer (ETL) improves the power conversion efficiency (PCE) of perovskite solar cells due to faster charge transport kinetics as well as slower charge recombination process. The optimized TiO2 nanocrystalline ETL (15 L) demonstrates as high as ~10% PCE with a short circuit current density of 18.0 mA/cm2, open circuit voltage of 0.81 V and fill factor of 66.3% in perovskite solar cells. Furthermore, room-temperature ammonia sensing characteristics of TiO2 nanocrystalline film (25 L) were demonstrated for various concentration levels of ammonia in dry air conditions. A high room-temperature response of 80% was achieved at 100 ppm of ammonia with rapid response and recovery signatures of 30 and 85 s, and nearly fifteen days stability, respectively. The response of the sensor to other gases such as formaldehyde, petrol, ethanol acetone, and ammonia etc, indicated a high selectivity towards volatile organic compounds of ammonia gas. The room temperature operation, with high selectivity, repeatability and fast transition times, suggests potentially useful in flexible and cost-effective production in optoelectrochemical device technology.
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