Vivekanand Kumar

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.

Photoelectrochemical activity of as-grown, α-Fe2O3 nanowire array electrodes for water splitting.

Undoped hematite nanowire arrays grown using plasma oxidation of iron foils show significant photoactivity (~0.38 mA cm(-2) at 1.5 V versus reversible hydrogen electrode in 1 M KOH). In contrast, thermally oxidized nanowire arrays grown on iron exhibit no photoactivity due to the formation of a thick (>7 μm Fe(1-x)O) interfacial layer. An atmospheric plasma oxidation process required only a few minutes to synthesize hematite nanowire arrays with a 1–5 μm interfacial layer of magnetite between the nanowire arrays and the iron substrate. An amorphous oxide surface layer on hematite nanowires, if present, is shown to decrease the resulting photoactivity of as-synthesized, plasma grown nanowire arrays. The photocurrent onset potential is improved after removing the amorphous surface on the nanowires using an acid etch. A two-step method involving high temperature nucleation followed by growth at low temperature is shown to produce a highly dense and uniform coverage of nanowire arrays.

Inorganic nanowires: a perspective about their role in energy conversion and storage applications

There has been tremendous interest and progress with synthesis of inorganic nanowires (NWs). However, much of the progress only resulted in NWs with diameters much greater than their respective quantum confinement scales, i.e. 10?100?nm. Even at this scale, NW-based materials offer enhanced charge transport and smaller diffusion length scales for improved performance with various electrochemical and photoelectrochemical energy conversion and storage applications. In this paper, these improvements are illustrated with specific results on enhanced charge transport with tin oxide NWs in dye sensitized solar cells, higher capacity retention with molybdenum oxide (MoO3) NW arrays and enhanced photoactivity with hematite NW arrays compared with their nanoparticle (NP) or thin film format counterparts. In addition, the NWs or one-dimensional crystalline materials with diameters less than 100?nm provide a useful platform for creating new materials either as substrates for heteroepitaxy or through the phase transformation with reaction. Specific results with single crystal phase transformation of hematite (a-Fe2O3) to pyrite (FeS2) NWs and heteroepitaxy of indium-rich InGaN alloy over GaN NW substrates are presented to illustrate the viability of using NWs for creating new materials. In terms of energy applications, it is essential to have a method for continuous manufacturing of vertical NW arrays over large areas. In this regard, a simple plasma-based technique is discussed that potentially could be scaled up for roll-to-roll processing of NW arrays.

Functionalizing titania nanoparticle surfaces in a fluidized bed plasma reactor

Functionalizing nanoparticle surfaces is essential for achieving homogeneous dispersions of monodisperse particles in polymer nanocomposites for successful utilization in engineering applications. Functionalization reduces the surface energy of the nanoparticles, thereby limiting the tendency to agglomerate. Moreover, reactive groups on the surface can also participate in the polymerization, creating covalent bonds between the inorganic and organic phases. In this paper, a fluidized bed inductively coupled plasma (FB-ICP) reactor is used to break apart the agglomerates and functionalize commercial TiO2 nanoparticle powders in a batch of several grams. The fluidized bed could be implemented into a continuous flow reactor, potentially making this a viable method to treat larger quantities of commercial powders. The particles are treated with acrylic acid (AA) and tetraethylorthosilicate (TEOS) plasma and the functionalized particles were collected separately from bulk powder. High resolution transmission electron microscopy (HRTEM) analysis showed that the particles were coated uniformly with polymer coatings with thicknesses around a few nanometers. Fourier-transformed infrared spectroscopy (FTIR) studies of the polymer-coated particles showed the presence of different functional groups (poly-acrylic acid/siloxane) similar to that present in the bulk films. The dispersion behavior of the TiO2 nanoparticles showed much improvement with reduced agglomerate size.