Nano-composite LiMnPO4 as new insertion electrode for electrochemical supercapacitors

S.R.S. Prabaharan,R. Anslin Star,Ajit R. Kulkarni,M.S. Michael 한국물리학회 2015 Current Applied Physics Vol.15 No.12

Nano-composite olivine LiMnPO4 (nC-LMP) was found to exhibit facile pseudo-capacitive characteristics in aqueous as well as non-aqueous electrolytes. We demonstrated employing nC-LMP as positive electrode in hybrid electrochemical capacitors namely Li-Ion hybrid capacitors (LIC). Adapting a simple CVD technique, nano-crystallites of LiMnPO4 were coated with carbon monolayers of ~2 nm thick to circumvent its poor intrinsic electronic conductivity. The novelty is that the single crystallites were intimately covered with carbon ring and networked to the neighboring crystallites via the continuous carbon wire-like connectivity as revealed from HRTEM analysis. Single electrode faradic capacitance of 3025 Fg-1 (versus standard calomel reference electrode) was deduced for carbon coated LMP, the highest reported hitherto in Li+ aqueous electrolytes. Employing nC-LMP as working electrode versus an activated carbon (AC), we obtained a high specific energy of 28.8 Wh kg-1 with appreciable stability in aqueous electrolytes whereas in nonaqueous electrolyte there is an obvious increase in energy density (35 Wh kg-1) due to wider potential window. That is, a full cell version of LIC, ACjLi+jLMP, was fabricated and demonstrated its facile cycling characteristics via removal/insertion of Li+ within nC-LMP (positive electrode) and the electrosorption of Li+ into mesoporous carbon (AC) (negative electrode). Such cells ensured a typical battery-like charging and EDLC-like discharging characteristics of LIC type electrochemical capacitors (ECs) which are desired to enhance safety and energy densities.

An FPGA Based Temperature Controller for Differential Thermal Analyzer

T. Nandha Kumar,Tarek Mohd A.K AL Saleh,,SRS.Prabaharan,Haider A.F. Mohamed 제어로봇시스템학회 2009 제어로봇시스템학회 국제학술대회 논문집 Vol.2009 No.8

Differential Thermal Analyzer (DTA) is an instrument used to characterize the new materials and it worksbased on the themoanalytic qualitatively technique. In this paper a digital design of a programmable temperature controller for the DTA has been presented. This programmable controller has been designed using very high speedintegrated circuit hardware description language (VHDL) and implemented in a field programmable gate array (FPGA). The heating rate of the DTA can be flexibly selected from the range between 1°C per minute and 15°C per minute. Also, the temperatures are measured with the accuracy of 0.125 degrees. The sampling time between the reference and thefeedback temperatures of the controller has been designed for 2.56 seconds. The simulations and experimental results of the proposed temperature controller are presented.

Molecular Characterization of Marine Cyanobacteria from the Indian Subcontinent Deduced from Sequence Analysis of the Phycocyanin Operon (cpcB-IGS-cpcA) and 16S-23S ITS Region

Premanandh, Jagadeesan,Priya, Balakrishnan,Teneva, Ivanka,Dzhambazov, Balik,Prabaharan, Dharmar,Uma, Lakshmanan The Microbiological Society of Korea 2006 The journal of microbiology Vol.44 No.6

Molecular characterization of ten marine cyanobacterial isolates belonging to the order Oscillatoriales was carried out using the phycocyanin locus (cpcBA-IGS) and the 16S-23S internally transcribed spacer region. DNA sequences from the phycocyanin operon discriminated ten genotypes, which corresponded to seven morphotypes identified by traditional microscopic analysis. The cpcB coding region revealed 17% nucleotide variation, while cpcA exhibited 29% variation across the studied species. Phylogenetic analyses support the conclusion that the Phormidium and Leptolyngbya genera are not monophyletic. The nucleotide variations were heterogeneously distributed with no or minimal informative nucleotides. Our results suggest that the discriminatory power of the phycocyanin region varies across the cyanobacterial species and strains. The DNA sequence analysis of the 16S-23S internally transcribed spacer region also supports the polyphyletic nature of the studied oscillatorian cyanobacteria. This study demonstrated that morphologically very similar strains might differ genotypically. Thus, molecular approaches comprising different gene regions in combination with morphological criteria may provide better taxonomical resolution of the order Oscillatoriales.

Molecular Characterization of Marine Cyanobacteria from the Indian Subcontinent Deduced from Sequence Analysis of the Phycocyanin Operon (cpcB-IGS-cpcA) and 16S-23S ITS Region

Jagadeesan Premanandh,Balakrishnan Priya,Ivanka Teneva,Balik Dzhambazov,Dharmar Prabaharan,Lakshmanan Uma 한국미생물학회 2006 The journal of microbiology Vol.44 No.6

Molecular characterization of ten marine cyanobacterial isolates belonging to the order Oscillatoriales was carried out using the phycocyanin locus (cpcBA-IGS) and the 16S-23S internally transcribed spacer region. DNA sequences from the phycocyanin operon discriminated ten genotypes, which corresponded to seven morphotypes identified by traditional microscopic analysis. The cpcB coding region revealed 17% nucleotide variation, while cpcA exhibited 29% variation across the studied species. Phylogenetic analyses support the conclusion that the Phormidium and Leptolyngbya genera are not monophyletic. The nucleotide variations were heterogeneously distributed with no or minimal informative nucleotides. Our results suggest that the discriminatory power of the phycocyanin region varies across the cyanobacterial species and strains. The DNA sequence analysis of the 16S-23S internally transcribed spacer region also supports the polyphyletic nature of the studied oscillatorian cyanobacteria. This study demonstrated that morphologically very similar strains might differ genotypically. Thus, molecular approaches comprising different gene regions in combination with morphological criteria may provide better taxonomical resolution of the order Oscillatoriales.

Design and Modeling of a Capacitor Bank Power Supply for Fast Charging

Surender Kumar Sharma,Pankaj Deb,R. Shukla,P. Banerjee,T. Prabaharan,R. Das,B. Das,B. Adhikary,A. Shyam 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61

Power supplies used in pulsed power applications are rugged, and the capacitor bank charges rapidly. The capacitor bank is fully charged to the rated voltage in a minimum time so as to reduce the dielectric stress on the capacitors and to increase their life. When the capacitor bank is discharged in the load much Electromagnetic Interference (EMI) and Electromagnetic Pulse (EMP) due to high currents discharges is generated, which can damage the electronic circuitry in the power supply if proper shielding & isolation are not provided to it. We have designed and fabricated a compact, rugged and low-cost high voltage (HV) power supply for a 114-kJ, 40-kV capacitor bank. The power supply consists of a high voltage transformer (5.25 kVA, 230 V/35 kV, 50 Hz), a high voltage diode (Semikron Make PIV 110 kV, 150 mA) and a charging resistor placed in a tank filled with oil. The charging resistors value is selected after a PSPICE simulation of the charging circuit for different values of the charging resistor. The charging current is limited with the selected resistor so that it does not exceed the current limit of the HV transformer & diode. The input voltage to the high voltage transformer is given through autotransformer, which rotates from 0 ?230 volts in 40 sec with a single-phase synchronous motor. The capacitor bank is charged to 40 kV in a minute after that, the power supply is decoupled from the capacitor bank by using a pneumatic decoupling switch, then the capacitor bank's switch is triggered to deliver the capacitor bank's energy to the load. Control and protection in the power supply is provided for its safe operation. The monitoring of charging voltage is done with a digital display meter with fiber optic isolation by using a V-F and then F-V converter in order to provide electrical isolation.

Fast Marx Generator for Directly Driving a Virtual Cathode Oscillator

Biswajit Adhikary,Anurag Shyam,R. Shukla,S. K. Sharma,P. Banerjee,P. Deb,T. Prabaharan,R. Das,B. K. Das 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.61

This paper presents the design, development and testing of a fast, compact hybrid-type Marx generator which is suitable to directly drive a high-power microwave producing virtual cathode oscillator. The developed Marx generator has an open circuit voltage of 300 kV, a pulse width of 640 ns (FWHM) and a rise time of 200 ns. The fast rise time is achieved by reducing the inductance of the discharge path with the help of specially designed spark gaps. The Marx generator operates in open air now, but will soon be placed in a container with insulation that will help to charge the stage capacitors to their maximum voltage rating repeatedly, it will also help to reduce the rise time further by bringing the return path close thus reducing the inductance. The Marx generator has six stages, and all stages are charged to same polarity, with 1.8 kJ being stored at full charge. The operational characteristics, such as the impedance, inductance, current- delivering capacity, rise time, etc; of the developed Marx generator are determined experimentally. A detailed study on the effect of loading on the generator and its performance is also conducted. The overall size of the generator without its container is 0.8m in length, 0.45m in height and 0.35m in width.

Nickel-cobalt oxide/activated carbon composite electrodes for electrochemical capacitors

Sook-Keng Chang,Zulkarnain Zainal,Kar-Ban Tan,Nor Azah Yusof,Wan Mohamad Daud Wan Yusoff,S.R.S. Prabaharan 한국물리학회 2012 Current Applied Physics Vol.12 No.6

Nanostructured synthesis of nickelecobalt oxide/activated carbon composite by adapting a coprecipitation protocol was revealed by transmission electron microscopy. X-ray diffraction analysis confirmed that nickelecobalt oxide spinel phase was maintained in the pure and composite phases. Cyclic voltammetry, galvanostatic chargeedischarge tests and ac impedance spectroscopy were employed to elucidate the electrochemical properties of the composite electrodes in 1.0 M KCl. The specific capacitance which was the sum of double-layer capacitance of the activated carbon and pseudocapacitance of the metal oxide increased with the composition of nickelecobalt oxide before showing a decrement for heavily-loaded electrodes. Utilisation of nickelecobalt oxide component in the composite with 50 wt. % loading displayed a capacitance value of ~59 F g-1. The prepared composite electrodes exhibited good electrochemical stability. Nanostructured synthesis of nickelecobalt oxide/activated carbon composite by adapting a coprecipitation protocol was revealed by transmission electron microscopy. X-ray diffraction analysis confirmed that nickelecobalt oxide spinel phase was maintained in the pure and composite phases. Cyclic voltammetry, galvanostatic chargeedischarge tests and ac impedance spectroscopy were employed to elucidate the electrochemical properties of the composite electrodes in 1.0 M KCl. The specific capacitance which was the sum of double-layer capacitance of the activated carbon and pseudocapacitance of the metal oxide increased with the composition of nickelecobalt oxide before showing a decrement for heavily-loaded electrodes. Utilisation of nickelecobalt oxide component in the composite with 50 wt. % loading displayed a capacitance value of ~59 F g-1. The prepared composite electrodes exhibited good electrochemical stability.