D. Velayutham

Ethyl viologen dibromide as a novel dual redox shuttle for supercapacitors

Viologen (1,1ʹ-diethyl-4,4ʹ-bipyridinium bromide) based redox active electrolyte in 1.0 M H2SO4 has been proposed as a novel electrolyte for supercapacitor (SC) applications due to its dual cathodic and anodic redox behaviour. Unlike other reported redox additives, viologen as a single redox species can improve the performance of both positive and negative electrodes simultaneously through the redox behaviour of bromide and 1,1ʹ-diethyl-4,4ʹ-bipyridinium ions. The synergic redox behaviour of the ions and their effect towards the enhancement of the electrochemical performance of the activated charcoal based SC are compared with those of neat H2SO4 and triethylbutylammonium bromide (N2224Br). The maximum specific capacitance of 408.0 F g−1 and specific energy of 23.0 W h kg−1 at 0.25 A g−1 were obtained for the viologen mediated SC. Interestingly, the specific capacitance continuously increased for the viologen mediated SC on charge–discharge cycling and 30% increment was observed at the end of 1000 cycles. The relaxation time constant is compared for SCs with viologen, neat H2SO4 and N2224Br electrolytes.

Investigations on the product distribution pattern during the electrochemical fluorination of 2-fluoropyridine and pyridine

Abstract By using 2-fluoropyridine instead of pyridine as the starting material, a 19% conversion yield of perfluoropiperidine was obtained during the electrochemical fluorination process. At least ten products including perfluoropiperidine were characterised using repeated fractional distillation followed by GC and NMR analysis.

Dye-sensitized solar cells containing mesoporous TiO2 spheres as photoanodes and methyl sulfate anion based biionic liquid electrolytes

Mesoporous TiO2 spheres (hereafter, MSs) were synthesized and incorporated into the photoanode of a quasi-solid state dye-sensitized solar cell (QSS-DSSC) containing an air stable ionic liquid electrolyte, namely 1-propyl-3-methylimidazolium iodide (PMII) along with triethylmethylammonium methyl sulfate (TEMAMS) (65 : 35 = v/v), in order to improve its performance. The presence of large pores in the MS, as confirmed using a high resolution scanning electron microscope (HR-SEM) and a mercury porosimeter, facilitates the penetration of QSS-electrolytes into the thin film, whereas their high surface area (108.1 m2 g−1) helps for high dye loading. Further, the large particle size increases the scattering ability of incident light leading to an excellent increment in the number of photons. The performance of DSSCs containing bi-ionic liquid (bi-IL) based electrolytes, namely, PMII/TEMAMS and PMII/1-ethyl-3-methylimidazolium tetrafluoborate (EMIBF4), with the addition of 0.2 M iodine, 0.4 M N-methylbenzimidazole (NMBI), and 0.15 M guanidiniumthiocyanate (GuSCN), was compared, where the DSSC based on PMII/TEMAMS bi-ILs demonstrates superior efficiency (6.18%) than that of PMII/EMIBF4 based one (4.53%). The DSSC with PMII/TEMAMS shows extraordinary durability and unfailing stability for 1200 h even though it was stored in the dark at 50 °C. Further, the PMII/TEMAMS bi-IL electrolyte shows a gel-state at room temperature naturally without adding any gelators or polymers.

ELECTROCHEMICAL FLUORINATION OF N,N,N',N'-TETRAMETHYLETHYLENEDIAMINE

Abstract The electrochemical fluorination of N,N,N′,N′ -tetramethylethylenediamine was carried out in a modified Simons type cell using anhydrous hydrogen fluoride as a solvent. Effects of various experimental parameters like concentration of amine, temperature, and current density etc. were investigated. In addition to perfluoro- N,N,N′,N′ -tetramethylethylenediamine, cyclic, cleavage, and partially fluorinated products were obtained and characterized by gas chromatography, IR spectroscopy, nuclear magnetic resonance and mass spectra. A plausible reaction pathway for the electrochemical fluorination of N,N,N′,N′ -tetramethylethylenediamine has been proposed based on the products obtained.

Cleavage path way and the product distribution pattern during the electrochemical perfluorination of tripropylamine

Abstract The electrochemical fluorination (ECF) of tripropylamine (TPA) was carried out in anhydrous hydrogen fluoride medium using a Simons type cell. Under optimum conditions, yield of perfluorinated product was about 51% and the selectivity of perfluorotripropylamine (PFTPA) was about 87%. Even in this process involving the well-known starting material, apart from PFTPA, about nine perfluorinated by-products were also identified. Perfluorinated products obtained were characterized by GC, 1 H and 19 F NMR spectra and were compared with reported values. The perfluorinated products obtained support the fission and formation of CC and CN bonds. The nature of the minor products formed also supports the involvement of cyclization and isomerization reactions during electrochemical fluorination. Suitable reaction schemes for the formation of different perfluorinated by-products were suggested based on the identified products obtained from ECF of TPA which clearly supports the free radical mechanistic pathway for this process.

A COMPARATIVE STUDY OF THE ELECTROCHEMICAL FLUORINATION (ECF) OF 1,N-ALKANEBIS (SULFONYLFLUORIDES) (N=1-3)

Abstract Synthetic methods for the preparation of α,ω -alkanebis(sulfonylfluorides) and their electrochemical fluorination (ECF) are described in detail. Factors affecting the yield of the perfluoro- α,ω -alkanebis(sulfonylfluorides) are also discussed. Spectral data ( 13 C and 19 F NMR and mass spectra) and other hitherto unknown physical properties of difluoromethanebis(sulfonylfluoride) ( 1 ), 1,1,2,2-tetrafluoroethane-1,2 bis (sulfonylfluoride) ( 2 ) and 1,1,2,2,3,3-hexafluoropropane-1,3-bis(sulfonylfluoride) ( 3 ) are measured and compared.

High rate performing in-situ nitrogen enriched spherical carbon particles for Li/Na-ion cells

Nitrogen rich, porous spherical carbon particle with the large surface area was synthesized by simple pyrolysis of the amorphous covalent organic framework. The obtained mesoporous spherical carbon particles with dilated interlayer distance (0.377 nm), large surface area (390 m2 g-1) and high level nitrogen doping (10.9%) offer eminent electrochemical performance as an anode for both lithium ion (LIBs) and sodium ion batteries (SIBs). In LIB applications, the synthesized material delivers an average reversible capacity of 820 mAh g-1 after 100 cycles at 0.1 A g-1, superior rate capability of 410 and 305 mAh g-1 at 4.0 and 8.0 A g-1 respectively. In SIBs, the material shows the stable reversible capacity of about 238 mAh g-1 for the studied 500 cycles at 0.5 A g-1. The rate and steady state cycling performance at high current densities are impressive, being as high as 165 mAh g-1 even after 250 cycles at 2.0 A g-1.

Reversible 2D Supramolecular Organic Frameworks encompassing Viologen Cation Radicals and CB[8]

Reversible 2D supramolecular organic frameworks encompassing branched viologen architectures and cucurbit[8]uril (CB[8]) were constructed and investigated. UV-vis investigation clearly indicates the formation and intermolecular dimerization of monocation radicals and their encapsulation into the hydrophobic CB[8] cavity which is further complemented by EPR (electron paramagnetic resonance) spectroscopy. Particle size measurements by dynamic light scattering method showed particle sizes in the range of several µm indicating larger aggregates. Zeta potential measurements suggested the instability of these particles and their tendency to form aggregates. TEM (transmission electron microscope) analysis further revealed the formation of supramolecular polymer (monocation radical with cucurbit[8]uril) whose diameter were in the range of several µm as indicated by DLS measurements; however the oxidized form, i.e., the viologen dication with cucurbit[8]uril showed dotted spots in the range of sub nanometer level. The internal periodicities of the supramolecular polymers were analyzed by SAXs (small angle X-ray scattering) measurements. Additionally, we have demonstrated that these supramolecular organic frameworks can be depolymerized by oxidation in air and again can be polymerized (intermolecular radical dimerization) by reduction under inert atmosphere demonstrating that these systems will be of broad interest.

High lithium anodic performance of N-doped porous biocarbon-integrated indium sulfide thin nanosheets

A mesoporous 3D marigold flower-like indium sulfide (In2S3) microstructure grafted with nitrogen-doped porous carbon nanosheets was synthesised from fish scale biowaste using a simple, scalable, and cost-effective method. The as-obtained composite exhibited a larger surface area (307 m2 g−1) than pristine InS (57 m2 g−1). As the anode in a lithium ion battery, the synthesised composite and pristine materials retained capacities of about 751 and 397 mA h g−1, respectively, after 100 cycles at a current density of 500 mA g−1. Furthermore, the composite material delivered capacities in the range 1260–297 mA h g−1 when the current density was varied from 0.025 to 10.0 A g−1. The impressive electrochemical performance of the composite material is associated with the synergetic effect of porous carbon nanosheets in alleviating volume expansion and enhancing reversibility, allowing practical application in lithium ion batteries.

A novel electrochemical sensor based on a nickel-metal organic framework for efficient electrocatalytic oxidation and rapid detection of lactate

Lactate serves as a biomarker for a plethora of microbial contamination in cow milk. In this context, a novel nickel-metal organic framework (Ni-MOF) modified platinum electrode was fabricated for the effective and reliable detection of lactate in cow milk samples. The Ni-MOF of mean size 12 μm in length and 0.7 nm in width was synthesized by an inexpensive mild solution method. The Ni-MOF modified platinum, platinum wire and Ag/AgCl were employed as the working, counter and reference electrodes to design a potentiostatic three-electrode configuration device. The developed Ni-MOF modified platinum electrode exhibits good sensitivities (106.617 and 29.533 μA mM−1) towards lactate over the wide linear ranges of 0.01–0.9 and 1–4 mM with a correlation coefficient of R2 = 0.99, a detection limit of 5 μM, a repeatability of 0.57% RSD and a stability of 95.3% for 20 days. The nano-flower like morphology of Ni-MOF provides accessible sites for the electro-oxidation of lactate and thereby high sensitivity to lactate. Furthermore, the developed electrode remained free from potential interfering species and thus provides a promising tool for rapid detection of lactate in cow milk samples.