Jitendra Kumar

A Solid-State, Rechargeable, Long Cycle Life Lithium–Air Battery

Abstract : This paper describes a totally solid-state, rechargeable, long cycle life lithium-oxygen battery cell. The cell is comprised of a Li metal anode, a highly Li-ion conductive solid electrolyte membrane laminate fabricated from glass-ceramic (GC) and polymer-ceramic materials, and a solid-state composite air cathode prepared from high surface area carbon and ionically conducting GC powder. The cell exhibited excellent thermal stability and rechargeability in the 30-105 C temperature range. It was subjected to 40 charge-discharge cycles at current Densities ranging from 0.05 to 0.25mA/sq cm. The reversible charge/discharge voltage profile of the Li-O2 cell with low polarizations between the discharge and charge are remarkable for a displacement-type electrochemical cell reaction involving the reduction of oxygen to form lithium peroxide. The results represent a major contribution in the quest of an ultra high energy density electrochemical power source. We believe that the Li-O2 cell, when fully developed, could exceed specific energies of 1000 Wh/kg in practical configurations.

Mesoporous Nitrogen-Doped Carbon-Glass Ceramic Cathodes for Solid-State Lithium–Oxygen Batteries

The composite of nitrogen-doped carbon (N-C) blend with lithium aluminum germanium phosphate (LAGP) was studied as cathode material in a solid-state lithium-oxygen cell. Composite electrodes exhibit high electrochemical activity toward oxygen reduction. Compared to the cell capacity of N-C blend cathode, N-C/LAGP composite cathode exhibits six times higher discharge cell capacity. A significant enhancement in cell capacity is attributed to higher electrocatalytic activity and fast lithium ion conduction ability of LAGP in the cathode.

Arsenophonus GroEL interacts with CLCuV and is localized in midgut and salivary gland of whitefly B. tabaci.

Cotton leaf curl virus (CLCuV) (Gemininiviridae: Begomovirus) is the causative agent of leaf curl disease in cotton plants (Gossypium hirsutum). CLCuV is exclusively transmitted by the whitefly species B. tabaci (Gennadius) (Hemiptera: Alerodidae). B. tabaci contains several biotypes which harbor dissimilar bacterial endo-symbiotic community. It is reported that these bacterial endosymbionts produce a 63 kDa chaperon GroEL protein which binds to geminivirus particles and protects them from rapid degradation in gut and haemolymph. In biotype B, GroEL protein of Hamiltonella has been shown to interact with Tomato yellow leaf curl virus (TYLCV). The present study was initiated to find out whether endosymbionts of B. tabaci are similarly involved in CLCuV transmission in Sriganganagar (Rajasthan), an area endemic with cotton leaf curl disease. Biotype and endosymbiont diversity of B. tabaci were identified using MtCO1 and 16S rDNA genes respectively. Analysis of our results indicated that the collected B. tabaci population belong to AsiaII genetic group and harbor the primary endosymbiont Portiera and the secondary endosymbiont Arsenophonus. The GroEL proteins of Portiera and Arsenophonus were purified and in-vitro interaction studies were carried out using pull down and co-immunoprecipitation assays. In-vivo interaction was confirmed using yeast two hybrid system. In both in-vitro and in-vivo studies, the GroEL protein of Arsenophonus was found to be interacting with the CLCuV coat protein. Further, we also localized the presence of Arsenophonus in the salivary glands and the midgut of B. tabaci besides the already reported bacteriocytes. These results suggest the involvement of Arsenophonus in the transmission of CLCuV in AsiaII genetic group of B. tabaci.

Cathodes for Solid-State Lithium–Oxygen Cells: Roles of Nasicon Glass-Ceramics

The roles of lithium aluminum germanium phosphate LAGP glass-ceramic GC in cathodes of totally solid-state lithium– oxygen Li–O2 electrochemical cells are delineated by conducting discharge experiments as a function of cathode chemistry. It is proposed that LAGP possesses an inherent characteristic to adsorb oxygen molecules due to its open structure. The adsorption is followed by reduction of oxygen to superoxide and peroxide molecules. Subsequently, these molecules react with lithium ions to form respective discharge products. In addition to being an important constituent of the cathode, the LAGP also serves as a solid-state electrolyte membrane due to its superionic lithium-ion conductivity. The dual functions of the LAGP GCs make it a feasible material to process an integrated membrane–cathode element of a Li–O2 cell, although this is not demonstrated in this paper.

Space-Charge-Mediated Superionic Transport in Lithium Ion Conducting Glass–Ceramics

This paper describes an investigation of the properties of superionic glass-ceramic specimens synthesized from the lithium-aluminum-germanium-phosphate system. The specimens were characterized using differential scanning calorimetry, X-ray diffraction, scanning electron microscopy, and impedance spectroscopy. The concentration of lithium oxide in the glass-ceramic formulations was the primary variable investigated. It is shown that the ionic conductivity of the specimens was dependent on the lithium oxide concentration. An optimized composition exhibited a conductivity approaching 10 ―2 S cm ―1 at around room temperature. The superionic conductivity in these specimens is attributed to the space-charge-mediated effect resulting from the presence of the dielectric Li 2 O phase. The specimens also displayed different conductivities during heating and cooling scans, referred to in this paper as hysteresis effect.

Diversity and phylogenetic analysis of endosymbiotic bacteria from field caught Bemisia tabaci from different locations of North India based on 16S rDNA library screening

Bemisia tabaci is the major vector pest of agricultural crops all over the world. In this study we report the different bacterial endosymbionts associated with B. tabaci sampled from 14 different locations in North India. Using 16S rDNA clone library sequences we were able to identify Portiera, the primary endosymbiont of B. tabaci, and other secondary endosymbionts like Cardinium, Wolbachia, Rickettsia and Arsenophonus. Along with these we also detected Bacillus, Enterobacter, Paracoccus and Acinetobacter. These secondary endosymbionts were not uniformly distributed in all the locations. Phylogenetic analysis of 16S rDNA sequences of Cardinium, Wolbachia, Rickettsia and Arsenophonus showed that each of these bacteria form a separate cluster when compared to their respective counterparts from other parts of the world. MtCO1 gene based phylogenetic analysis showed the presence of Asia I and Asia II genetic groups of B. tabaci in N. India. The multiple correspondence analyses showed no correlation between the host genetic group and the endosymbiont diversity. These results suggest that the bacterial endosymbiont diversity of B. tabaci is much larger and complex than previously perceived and probably N. Indian strains of the bacterial symbionts could have evolved from some other ancestor.

Structure–conductivity correlation in ferric chloride-doped poly(3-hexylthiophene)

Poly(3-hexylthiophene) (P3HT) matrix has been chemically doped (redox doping) by ferric chloride (FeCl3) with different molar concentrations to get P3HT–FeCl3 charge-transfer complexes. The effect of redox doping on photo-physical, structural, and morphological properties and dc electrical conductivity of P3HT matrices has been examined. The dc conductivity has been measured on films of pristine P3HT and P3HT–FeCl3 charge-transfer complexes in the temperature range 6–300 K. Analysis of dc conductivity data reveals that in the temperature range 40–300 K, the dc conductivity is predominantly governed by Motts 3-dimensional variable range hopping (3D-VRH); however, below 40 K tunnelling seems to dominate. A slight deviation from 3D-VRH to 1D-VRH is observed with an increase in doping level or precisely with an increase in the extent of P3HT–FeCl3 charge-transfer complexes. We attribute this deviation to the induced expansion in crystallographic lattices as revealed by x-ray diffraction data and formation of discrete conducting domains as observed by atomic force microscope imaging.

dc electrical conduction and morphology of poly(3-octylthiophene) films

The surface morphology and electrical conductivity of poly(3-octylthiophene) (P3OT) films, in both their pristine and doped states, have been studied by scanning electron microscopy and by measuring the conductivity at room temperature and the variation of conductivity with temperature in the range 10-300 K. Pristine P3OT film exhibits a mat-type structure whereas ferric chloride doped P3OT film shows conducting domains in the range 40-80 nm. The room temperature dc conductivities of pristine and doped P3OT films are similar to 1 x 10(-8) S cm(-1) and 8.2 x 10(-4) S cm(-1), respectively. The temperature dependence of dc conductivity in the region 77-300 K, where hopping conduction dominates, is well described by Motts three-dimensional variable range hopping transport.

Band gap narrowing in zinc oxide-based semiconductor thin films

A simple expression is proposed for the band gap narrowing (or shrinkage) in semiconductors using optical absorption measurements of spin coated 1 at. % Ga-doped ZnO (with additional 0–1.5 at. % zinc species) thin films as ΔEBGN = Bn1/3 [1 − (nc/n)1/3], where B is the fitting parameter, n is carrier concentration, and nc is the critical density required for shrinkage onset. Its uniqueness lies in not only describing variation of ΔEBGN correctly but also allowing deduction of nc automatically for several M-doped ZnO (M: Ga, Al, In, B, Mo) systems. The physical significance of the term [1 − (nc/n)1/3] is discussed in terms of carrier separation.

Mechanism of charge transport in poly(3-octylthiophene)

The direct current (dc) conductivity (σdc) of pristine and ferric chloride doped poly(3-octylthiophene) has been measured in the temperature range of 6–300K. Mott’s three-dimensional variable range hopping and thermally activated tunneling are suggested as the dominant mechanisms of dc conduction at high (77–300K) and low (<77K) temperature regions, respectively.