Mahendra K. Sunkara

Core–shell MoO3–MoS2 Nanowires for Hydrogen Evolution: A Functional Design for Electrocatalytic Materials

We synthesize vertically oriented core-shell nanowires with substoichiometric MoO(3) cores of ∼20-50 nm and conformal MoS(2) shells of ∼2-5 nm. The core-shell architecture, produced by low-temperature sulfidization, is designed to utilize the best properties of each component material while mitigating their deficiencies. The substoichiometric MoO(3) core provides a high aspect ratio foundation and enables facile charge transport, while the conformal MoS(2) shell provides excellent catalytic activity and protection against corrosion in strong acids.

Accelerating materials development for photoelectrochemical hydrogen production: standards for methods, definitions, and reporting protocols

Photoelectrochemical (PEC) water splitting for hydrogen production is a promising technology that uses sunlight and water to produce renewable hydrogen with oxygen as a by-product. In the expanding field of PEC hydrogen production, the use of standardized

Hybrid Tin Oxide Nanowires as Stable and High Capacity Anodes for Li-Ion Batteries

In this report, we present a simple and generic concept involving metal nanoclusters supported on metal oxide nanowires as stable and high capacity anode materials for Li-ion batteries. Specifically, SnO(2) nanowires covered with Sn nanoclusters exhibited an exceptional capacity of >800 mAhg(-1) over hundred cycles with a low capacity fading of less than 1% per cycle. Post lithiation analyses after 100 cycles show little morphological degradation of the hybrid nanowires. The observed, enhanced stability with high capacity retention is explained with the following: (a) the spacing between Sn nanoclusters on SnO(2) nanowires allowed the volume expansion during Li alloying and dealloying; (b) high available surface area of Sn nanoclusters for Li alloying and dealloying; and (c) the presence of Sn nanoclusters on SnO(2) allowed reversible reaction between Sn and Li(2)O to produce both Sn and SnO phases.

Bulk synthesis of silicon nanowires using a low-temperature vapor–liquid–solid method

Silicon nanowires will find applications in nanoscale electronics and optoelectronics both as active and passive components. Here, we demonstrate a low-temperature vapor–liquid–solid synthesis method that uses liquid-metal solvents with low solubility for silicon and other elemental semiconductor materials. This method eliminates the usual requirement of quantum-sized droplets in order to obtain quantum-scale one-dimensional structures. Specifically, we synthesized silicon nanowires with uniform diameters distributed around 6 nm using gallium as the molten solvent, at temperatures less than 400 °C in hydrogen plasma. The potential exists for bulk synthesis of silicon nanowires at temperatures significantly lower than 400 °C. Gallium forms a eutectic with silicon near room temperature and offers a wide temperature range for bulk synthesis of nanowires. These properties are important for creating monodispersed one-dimensional structures capable of yielding sharp hetero- or homointerfaces.

MoO 3−x Nanowire Arrays As Stable and High-Capacity Anodes for Lithium Ion Batteries

In this study, vertical nanowire arrays of MoO(3-x) grown on metallic substrates with diameters of ~90 nm show high-capacity retention of ~630 mAhg(-1) for up to 20 cycles at 50 mAg(-1) current density. Particularly, they exhibit a capacity retention of ~500 mAhg(-1) in the voltage window of 0.7-0.1 V, much higher than the theoretical capacity of graphite. In addition, 10 nm Si-coated MoO(3-x) nanowire arrays have shown a capacity retention of ~780 mAhg(-1), indicating that hybrid materials are the next generation materials for lithium ion batteries.

Spontaneous Growth of Superstructure α‐Fe2O3 Nanowire and Nanobelt Arrays in Reactive Oxygen Plasma

One-dimensional a-Fe2O3 is a promising nanomaterial for advanced applications in catalysis and water splitting, environmental protection, sensors, dye solar cells, magnetic storage media, bioprocessing, and controlled drug delivery and detection, especially as carriers of antigens for prion detection and PCR manipulation. a-Fe2O3 nanowires have been successfully synthesized by various methods based on templates, hydrothermal conditions, sol–gel-mediated reactions, solvothermal conditions, gas decomposition, direct thermal oxidation (in a gas atmosphere of CO2, SO2, O2, and NO2), [7] chemical vapor deposition (CVD), and plasmaenhanced chemical vapor deposition (PECVD). The methods based on direct thermal oxidation, gas decomposition, and CVD reported to date require long synthesis times and high temperatures and therefore limit the efficiency of oxide nanowire synthesis. The application and commercialization of nanowires or nanobelts requires simple synthetic methods that can be scaled for both large areas and large quantities. Recently, we discovered a new universal method for the synthesis of transition metal oxide nanowires and nanobelts by direct plasma oxidation of bulk materials. It has been successfully applied for the rapid synthesis of high-density niobium oxide nanowires. In this process, there is no

Plasma Catalysis: Synergistic Effects at the Nanoscale.

Thermal-catalytic gas processing is integral to many current industrial processes. Ever-increasing demands on conversion and energy efficiencies are a strong driving force for the development of alternative approaches. Similarly, synthesis of several functional materials (such as nanowires and nanotubes) demands special processing conditions. Plasma catalysis provides such an alternative, where the catalytic process is complemented by the use of plasmas that activate the source gas. This combination is often observed to result in a synergy between plasma and catalyst. This Review introduces the current state-of-the-art in plasma catalysis, including numerous examples where plasma catalysis has demonstrated its benefits or shows future potential, including CO2 conversion, hydrocarbon reforming, synthesis of nanomaterials, ammonia production, and abatement of toxic waste gases. The underlying mechanisms governing these applications, as resulting from the interaction between the plasma and the catalyst, render the process highly complex, and little is known about the factors leading to the often-observed synergy. This Review critically examines the catalytic mechanisms relevant to each specific application.

Near-infrared semiconductor subwavelength-wire lasers

We report near-infrared lasing in the telecommunications band in gallium antimonide semiconductor subwavelength wires. Our results open the possibility of the use of semiconductor subwavelength-wire lasers in future photonic integrated circuits for telecommunications applications.

Surface properties of SnO2nanowires for enhanced performance with dye-sensitized solar cells

Our recent studies showed that nanowire based DSSCs exhibited over 250 mV higher open circuit potentials (VOC) compared to those using nanoparticles. In this study, the electron transport and surface properties of nanowires and nanoparticles are investigated to understand the reasons for the observed higher photovoltages with NW based solar cells. It was seen that, in addition to slow recombination kinetics, the lower work function of SnO2nanowires compared to the nanoparticle counterparts also significantly contributes to the high VOC observed for the nanowire based DSSCs.

Diamond Growth at Low Pressures

Diamond synthesis has attracted attention ever since it was established in 1797 that diamond is a crystalline form of carbon. Initially, synthesis was attempted at high pressures because diamond is the densest carbon phase. As understanding of chemical thermodynamics developed through the 19th and 20th centuries, the pressure-temperature range of diamond stability was explored. These efforts culminated in the announcement in 1955 of a process for diamond synthesis with a molten transition metal solvent-catalyst at pressures where diamond is thermo-dynamically stable. Worldwide sales of synthetic diamond now approach 330 million carats (73 tons) with a market price of between