Murugavel Kathiresan

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.

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.

Charge–discharge studies of all-solid-state Li/LiFePO4 cells with PEO-based composite electrolytes encompassing metal organic frameworks

Lithium batteries with high energy density can be achieved only with a metallic-lithium anode in conjunction with solid polymer electrolyte. Unfortunately, the undesirable interfacial properties and the subsequent formation of a solid electrolyte interface (SEI) layer and poor ionic conductivity at ambient temperature hamper this system from being commercialized. In order to conquer these issues, numerous attempts have been made. Herein we report the preparation and electrochemical properties of a nickel-1,3,5-benzene tricarboxylate metal organic framework (Ni3–(BTC)2–MOF) laden-composite polymer electrolyte with a lithium salt (LiTFSI). The added Ni3–(BTC)2–MOF plays a vital role in enhancing the ionic conductivity, and the mechanical and thermal properties. The scavenging properties of the highly porous MOF significantly improved the Li/electrolyte interfacial properties. A 2032-type coin cell composed of Li/CPE/LiFePO4 was assembled and its cycling profile is discussed.

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.

Iron oxide decorated N-doped carbon derived from poly(ferrocene-urethane) interconnects for the oxygen reduction reaction

We report the synthesis of mixed iron oxide particles decorated on nitrogen-doped carbon by forming covalent polyurethane linkages between ferrocene and phloroglucinol. Contrasting the electrostatic interactions and the physical cross-linking of the Fe/N/C precursors, here poly(ferrocene-urethane) (PFU) was acquired exclusively by (i) conversion of dicarboxylic acids present in ferrocene to azide linkages; and (ii) chemically linking the ferrocene-diazides to phloroglucinol through urethane bonds. The as obtained poly(ferrocene-urethane) was pyrolyzed under argon at elevated temperatures (600, 800 and 1000 °C) to yield iron oxide decorated N-doped carbon interconnects. The resultant porous materials were found to have the right balance of hierarchical porosity (micro-, meso- and macro-), and N-doping and iron oxide phases in and on the carbon matrices, respectively. Among the PFU samples pyrolyzed at different temperatures, the sample pyrolyzed at 800 °C displayed a more positive onset potential, a higher current density, and direct four electron transfer kinetics with a lesser yield of H2O2 (5.6%) on par with the commercially available Pt catalysts for the oxygen reduction reaction (ORR) in alkaline KOH solution. The superior electrocatalytic activity of PFU-800 can be traced to the synergistic effect between the iron oxide on and N-doping of the porous carbon nanostructures and the balanced hierarchial porosity. The developed non-Pt based electrocatalyst can be considered as a promising electrocatalyst in alkaline fuel cell applications.

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.

Porous Organic Polymer-Derived Carbon Composite as a Bimodal Catalyst for Oxygen Evolution Reaction and Nitrophenol Reduction

Ethylene diamine-based porous organic polymer (EPOP) was synthesized, carbonized at different temperatures, and characterized. The successful formation of the triazine polymer was confirmed by Fourier-transform infrared spectroscopy, 13C, and 15N cross-polarization magic angle spinning solid-state NMR. The two-dimensional layered architecture and graphitic nature of the samples resembled that of nitrogen-doped amorphous carbon, as confirmed by Raman, powder X-ray diffraction, and transmission electron microscopy measurements. The catalytic activity of these materials toward nitrophenol reduction and electrocatalytic activity toward oxygen evolution reaction (OER) were systematically evaluated in detail. Electrocatalytic activity toward oxygen evolution reaction was systematically evaluated by chronoamperometry and linear sweep voltammetry. Results clearly demonstrate that all of these catalysts exhibit good OER activity and excellent stability. Among all catalysts, EPOP-700 showed better OER activity, as reflected by its onset potential and current density, comparable with that of the metal-based OER catalysts and better than that of metal-free catalysts. Further, their catalytic activity toward the reduction of 4-nitrophenol to 4-aminophenol was tested with NaBH4; although all of these catalysts showed good catalytic activity; EPOP-800 displayed better catalytic activity.