Manganese-cobalt oxide as an effective bifunctional cathode for rechargeable Zn-air batteries with a compact quad-cell battery design.

Metal-air batteries, which are economical and ecological alternatives to Li-ion batteries, have become an important energy storage system. In this study, bimetallic oxides of widely accepted transition metal oxides like MnCo2O4 and NiFe2O4 have been explored to fabricate an efficient rechargeable Zn-air battery. The synthesis of these materials involves a single step direct decomposition of constituent metallic salts using polyvinyl pyrrolidone as a stabilizer cum nanostructure growth modifier by a simple open-air spray pyrolysis. The well characterized materials are used as cathodes in the assembly of a Zn-air battery that delivers a decent specific capacity of 780.1 mA h g-1. It also offers long term charge-discharge for more than 900 cycles with a week-long break-free operational stability under a small voltage gap (0.65-0.73 V). Finally, a unique and compact quad-cell solid state battery design has been introduced using these cathodes and chemically modified anodes resembling the commercial lithium-ion mobile phone battery. This tiny portable Zn-air battery displays an open circuit potential (OCP) of 4.46 V.

Tuning DNA electrical conductivity by silver photo-doping.

Photodoping of silver into bulk DNA is studied by measuring its ambient electrical conductivity. Mechanically pressed pellets of pure DNA and chemically modified Ag-DNA were prepared and were further coated with silver paste on either side of pellets to monitor the photodoping process. The electrical conductivity of these pellets was continuously measured under white light irradiation. The initial electrical conductivity of these pellets was smaller, that progressively increased with increase in number of current-voltage scan cycles under constant illumination of visible light. The change in electrical conductivity by photodoping is more in a pure DNA as compared to that of chemically modified Ag-DNA. The temperature dependent electrical conductivity exhibits the Arrhenius behavior. A detailed elemental depth profile was studied by core level x-ray photo-electron spectroscopy (XPS). The results clearly suggest that photodoping of silver can alter the DNA's starting electrical conductivity.

Large-scale synthesis of copper sulfide by using elemental sources via simple chemical route.

Copper sulfide is a low-cost and non-toxic material which is very attractive and promising for various applications. There is a need of a large-scale production of this material by simple methods. Here, a simple and ambient method is proposed for a large-scale preparation of copper sulfide. The synthesis is carried out at room temperature by using ultrasonication method where the elemental precursors, copper and sulfur are directly used. The present method gives gram scale synthesis with high yield in a short period of time. The materials are characterized by different techniques, their electrical conductivity and Seebeck coefficient are also measured and analyzed. The present method is one of the simple ways of producing copper sulfide just at room temperature.

A Simple and Portable Setup for Thermopower Measurements.

Thermoelectric energy conversion technology has received significant attention because of its promising applications and environmentally clean nature. The innovative design of efficient thermoelectric materials is assisted by simple and reliable techniques for fast and accurate testing. Here, a simple approach for rapid measurement of the Seebeck coefficient is described using commonly available materials based on hot and cold probes; both probes are heated by built-in microheaters. A spring-loaded sample mounting arrangement provides easy sample loading/unloading. The setup is suitable for measurements on a wide range of materials, such as pellets, films, and even soft surfaces without damage. Several known thermoelectric materials, such as alumel, bismuth, and silicon, yielded values close to reported ones. The setup is very compact, simple, fast, low cost, and reliable to develop as a laboratory characterization tool.

Ambient synthesis and characterization of high-quality CdSe quantum dots by an aqueous route.

Herein, we report the ambient synthesis of CdSe nanoparticles of widely tunable particle size by a solution route. The proposed protocol uses hydrazine hydrate to form an air-stable complex of selenium. These nanoparticles are characterized by X-ray diffraction, FTIR, optical absorption, photoluminescence, and transmission electron microcopy measurements. By varying the molarities of Cd(2+) and Se(2-) ions in solution with 3-mercaptopropionic acid as the capping ligand, the method permits us to synthesize nanoparticles of size ranging from 1.58 to 3.42 nm (estimated from optical absorption edge measurements) by controlling the annealing time of the starting colloid at 100 degrees C. The extracted quantum dots are of high quality (40% photoluminescence quantum yield) and exhibit colors ranging from deep blue to red. The resulting colloids are very stable, and no precipitate is observed over a period of 6 months. Thus, the method is simple and easily scalable to synthesize fluorescent CdSe nanoparticles.

Formation of electronic junctions on molecularly modified surfaces by lift-and-float electrical contacts.

Here, we report a simple method of forming electrical contacts on soft surfaces of organic monolayers and organically capped nanoparticles. It is based on the lift of predefined contacts of silver paste on a water surface and their pickup and float on a soft surface by capillary force. Three different surfaces of silicon--hydrogen terminated, covalently bonded organic molecules, and a thin film of organically capped CdSe nanoparticles--were used to constitute electronic junctions by lift and float of individual contacts. Charge transport measurements clearly demonstrate that these junctions are free from shorting and wrinkling of the top contact and damage of molecular films. Hence, the method is simple, effective, nondestructive, and economical to form electronic junctions on molecular surfaces.

Molecularly controlled metal-semiconductor junctions on silicon surface: a dipole effect.

Silicon surface was chemically modified by covalent attachment of homologous organic molecules having different dipole moments. Surface photovoltage measurements clearly confirm that organic molecules have a profound effect on surface band bending of semiconductor. Metal-molecules--silicon junctions were constituted for molecules belonging to ethynylbenzene series using soft mercury contact. These junctions show a systematic change in the electrical charge transport with dipole moment of molecules. Parameters such as ideality factor, barrier height, and density of interface states of various junctions are estimated to understand the role of organic molecules. These studies offer the prospect to develop molecular electronics, which may find potential applications in solar cells and chemical and biological sensors.