Pravin S. Walke

A single In-doped SnO2 submicrometre sized wire as a field emitter

Indium doped tin oxide submicrometre sized wires have been synthesized by thermal evaporation and characterized by field emission (FE) microscopy. The non-linear Fowler?Nordheim plot corresponds to the typical semiconducting behaviour of the emitter. The field enhancement factor has been estimated to be 29?900?cm?1 indicating that electron emission is due to the nanometric features of the emitter. A current density of the order of 6.36 ? 103?A?cm?2 with an applied electric field of 1 ? 104?V??m?1 has been obtained. The long term FE current stability tested at the preset current level of 1??A exhibits no severe fluctuations.

Pt-nanoparticle functionalized carbon nano-onions for ultra-high energy supercapacitors and enhanced field emission behaviour

In the present work, we have investigated the charge storage capacitive response and field emission behaviour of platinum (Pt) nanoparticles decorated on carbon nano onions (CNOs) and compared them with those of pristine carbon nano onions. The specific capacitance observed for Pt–CNOs is 342.5 F g−1, about six times higher than that of pristine CNOs, at a scan rate of 100 mV s−1. The decoration with Pt nanoparticles, without any binder or polymer separator on the CNO, leading to enhanced supercapacitance is due to easy accessibility of Na2SO4 electrolyte in the active material. The Density Functional Theory (DFT) calculations of these systems reveal enhancement in the Density of States (DOS) near the Fermi energy (EF) on account of platinum decoration on the CNOs. Furthermore, the field emission current density of ∼0.63 mA cm−2 has been achieved from the Pt-CNOs emitter at an applied electric field of ∼4.5 V μm−1 and from the pristine CNOs sample current density of ∼0.4 mA cm−2 has been achieved at an applied electric field of ∼6.6 V μm−1. The observed enhanced field emission behavior has been attributed to the improved electrical conductivity and increased emitting sites of the Pt–CNO emitter. The field emission current stability of the Pt–CNO emitter over a longer duration is found to be good. The observed results imply multifunctional potential of Pt–CNOs, as supercapacitor material in various next generation hybrid energy storage devices, and field emitters for next generation vacuum nano/microelectronic devices.

Unusual enhancement in the electroreduction of oxygen by NiCoPt by surface tunability through potential cycling

Chemically ordered interconnected nanostructures of NiCoPt alloy have been prepared using a simple solvothermal process and studied for oxygen reduction reaction (ORR) kinetics. NiCoPt/C catalyst has demonstrated an interesting trend of enhancement in the ORR activity along with long-term durability. The specific activity of 0.744 mA cm−2 for NCP10/C (NiCoPt/C prepared at reaction time of 10 h) is ∼3.7 times higher than that of Pt/C (0.2 mA cm−2). The durability of the catalyst was evaluated over 30k potential cycles in the lifetime regime. More significantly, a novel trend in the enhancement in the ORR activity during stability cycles has been observed for the first time, where a remarkable enhancement of 82% in the specific activity has been observed after 30k potential cycles. Thus, ∼7-fold higher activity of NCP10/C@30k over initial activity of commercial Pt/C would make a tremendous impact on fuel cell technology. Systematic X-ray diffraction studies were performed to supplement subsequent improvement in the ORR activity during potential cycling, where structural changes due to alloying and de-alloying taking place with formation of tetrahexahedron-like surfaces after 15k cycles. Furthermore, transmission electron microscopy (TEM) analysis after 30k durability cycles reveals better stability of NCP10/C nanostructure signifying the retention of Ni and Co due to the chemically ordered structures of NiCoPt alloy catalyst. The observed enhancement in durability might be due to the ordered arrangement of Pt and Ni/Co within the alloy.

Effect of solvents in the extraction and stability of anthocyanin from the petals of Caesalpinia pulcherrima for natural dye sensitized solar cell applications

Anthocyanin, a flavonoid pigment is responsible for wide range of coloration in petals of flowers and fruits, absorbs broad range of visible light. This makes them suitable to be used as dyes for DSSC. But, the efficiency of natural dyes is not up to the mark mainly due to anthocyanin instability. The stability issues in vitro are mainly due to the effect of solvents on extraction of anthocyanins and their respective pH. Taking this factor into consideration, in the present work, the anthocyanins were extracted from the flower Caesalpinia pulcherrima (C. pulcherrima) with various solvents and their respective stability and pH values are discussed. The usage of citric acid as solvent to extract anthocyanin has shown good stability than other solvents. It also helps in enhancing the sensitization properties of anthocyanins with titanium dioxide (TiO2) nanorods. The IPCE spectra show higher photovoltaic performance for dye sensitized TiO2 nanorods using citric acid as solvent. The natural DSSC using citric acid as solvent shows a higher efficiency of 0.83% compared to other solvents. Hence citric acid performs to be a safe solvent for natural DSSC in boosting the photovoltaic performance and maintaining the stability of anthocyanins.

Morphological, structural and field emission characterization of hydrothermally synthesized MoS2-RGO nanocomposite

A few layered MoS2-RGO nanocomposite has been synthesized employing a facile hydrothermal synthesis route. The morphological and structural analysis performed using SEM, TEM, HRTEM and Raman spectroscopy clearly reveal formation of vertically aligned a few layer thick MoS2 sheets on RGO surface. Attempts have been made to reveal the influence of graphite oxide (GO) percentage on morphology of the nanocomposite. Furthermore, field emission (FE) investigations of as-synthesied MoS2-RGO nanocomposite are observed to be superior to the pristine MoS2 emitter. The values of turn-on field, defined at emission current density of 10 μA cm−2, are found to be 2.6 and 4.7 V μm−1 for the MoS2-RGO (5%) nanocomposite and pristine MoS2 emitters, respectively. The value of threshold field, defined at emission current density of 100 μA cm−2, is found to be 3.1 V μm−1 for MoS2-RGO nanocomposite. The emission current stability at the pre-set value of 1 μA over 3 h duration is found to be fairly good, characterized by current fluctuation within ±18% of the average value. The enhanced FE behavior for MoS2-RGO nanocomposite is attributed to a high enhancement factor (β) of 4128 and modulation of the electronic properties. The facile approach adopted herein can be extended to enhance various functionalities of other nanocomposites.