Chitturi Venkateswara Rao

LiNi1/3Co1/3Mn1/3O2–Graphene Composite as a Promising Cathode for Lithium-Ion Batteries

The use of graphene as a conductive additive to enhance the discharge capacity and rate capability of LiNi(1/3)Co(1/3)Mn(1/3)O(2) electrode material has been demonstrated. LiNi(1/3)Co(1/3)Mn(1/3)O(2) and its composite with graphene (90:10 wt %) were prepared by microemulsion and ball-milling techniques, respectively. The structural and morphological features of the prepared materials were investigated with powder X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. Characterization techniques depict single-phase LiNi(1/3)Co(1/3)Mn(1/3)O(2) with particle sizes in the range of 220-280 nm. Electrochemical studies on LiNi(1/3)Co(1/3)Mn(1/3)O(2) and LiNi(1/3)Co(1/3)Mn(1/3)O(2)-graphene were conducted using cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy methods by constructing a lithium half-cell. Cyclic voltammograms show the well-defined redox peaks corresponding to Ni(2+)/Ni(4+). Charge-discharge tests were performed at different C rates: 0.05, 1, and 5 between 2.5 and 4.4 V. The results indicate the better electrochemical performance of the LiNi(1/3)Co(1/3)Mn(1/3)O(2)-graphene composite in terms of high discharge capacity (188 mAh/g), good rate capability, and good cycling performance compared to LiNi(1/3)Mn(1/3)Co(1/3)O(2). The improved electrochemical performance of the LiNi(1/3)Co(1/3)Mn(1/3)O(2)-graphene composite is attributed to a decrease in the charge-transfer resistance.

Free standing graphene-diamond hybrid films and their electron emission properties

Free standing graphene-diamond hybrid films have been fabricated using saturated hydrocarbon polymers as seeding material by hot filament chemical vapor deposition technique. The films are characterized with x-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron energy loss spectroscopy (EELS). The XRD shows the characteristic diffraction peaks of both diamond and graphene. The Raman spectrum shows the characteristic band of diamond at 1332 cm−1 and D, G, and 2D bands of graphene at 1349, 1592, and 2687 cm−1, respectively. Both SEM and TEM depict the presence of diamond and graphene in the films. The EELS recorded in the carbon K-edge region also shows the signature peaks of diamond and graphene. The free standing hybrid films exhibit a remarkably low turn-on field of about 2.4 V/μm and a high emission current density of 0.1 mA/cm2. Furthermore, emission currents are stable over the period of 7 days. The superior field emission...

Graphene-Supported Pt, Ir, and Pt-Ir Nanoparticles as Electrocatalysts for the Oxidation of Ammonia

Graphene oxide nanosheets are used as a support to anchor metal ions and produce graphene–metal nanoparticle hybrids in a sol–gel method. The influence of experimental conditions on the features of graphene-supported Pt, Ir, and Pt-Ir alloy nanoparticles is studied using transmission electron microscopy. Good dispersion of metal nanoparticles on the graphene sheets are observed for the catalysts heat-treated under exposure to N2 gas. The existence of metal species with zero oxidation state in the prepared catalysts is evident from the X-ray photoelectron spectroscopy. The characteristic X-ray diffraction peaks of Pt are observed for the graphene-supported Pt and Pt-Ir catalysts. Electrochemical activity of the finely dispersed catalysts toward ammonia oxidation is investigated using cyclic voltammetry. The performance increased in the order Ir < Pt ≈ Pt-Ir.

Temporal field emission current stability and fluctuations from graphene films

Stable field emission currents and low fluctuations are important feasibility requirements for the application of materials in field emission devices and displays. The current stability and current fluctuations of field emitted electrons from graphene films are investigated for the periods of 24 and 100 h. The graphene films showed different percentage of variation from the initial current density for different films ranging from 6% to 46% and the standard deviation in the range of 2–6 μA/cm2. The short- and long-term stability and fluctuations of the graphene films are reported and the causes for degradation of the emission current are discussed.