Kaveripatnam S. Dhathathreyan

Flexible Polyester Cellulose Paper Supercapacitor with a Gel Electrolyte

A low-cost polyester cellulose paper has been used as a substrate for a flexible supercapacitor device that contains aqueous carbon nanotube ink as the electrodes and a polyvinyl alcohol (PVA)-based gel as the electrolyte. Gel electrolytes have attracted much interest due to their solvent-holding capacity and good film-forming capability. The electrodes are characterized for their conductivity and morphology. Because of its high conductivity, the conductive paper is studied in supercapacitor applications as active electrodes and as separators after coating with polyvinylidene fluoride. Carbon nanotubes deposited on porous paper are more accessible to ions in the electrolyte than those on flat substrates, which results in higher power density. A simple fabrication process is achieved and paper supercapacitors are tested for their performance in both aqueous and PVA gel electrolytes by using galvanostatic and cyclic voltammetry methods. A high specific capacitance of 270 F g(-1) and an energy density value of 37 W h kg(-1) are achieved for devices with PVA gel electrolytes. Furthermore, this device can maintain excellent specific capacitance even under high currents. This is also confirmed by another counter experiment with aqueous sulfuric acid as the electrolyte. The cycle life, one of the most critical parameters in supercapacitor operations, is found to be excellent (6000 cycles) and less than 0.5 % capacitance loss is observed. Moreover, the supercapacitor device is flexible and even after twisting does not show any cracks or evidence of breakage, and shows almost the same specific capacitance of 267 F g(-1) and energy density of 37 W h kg(-1) . This work suggests that a paper substrate can be a highly scalable and low-cost solution for high-performance supercapacitors.

Synthesis of mesoporous Pt-Ru alloy particles with uniform sizes by sophisticated hard-templating method.

Team work: Mesoporous Pt-Ru alloy particles with uniform sizes are synthesized by controlled chemical reduction with ascorbic acid using mesoporous silica as a hard template. Elemental mapping shows uniform distribution of Pt and Ru particles. The electrochemical activity and stability of the alloys towards methanol oxidation much higher than that of mesoporous Pt and commercial Pt catalyst.

Investigation of a Novel Metal Hydride Electrode for Ni-Mh Batteries

The science and technology of a nickel metal hydride battery that stores hydrogen in the solid hydride phase has many advantages, including high energy density, high power, long life, tolerance to abuse, wide range of operating temperatures, quick-charge capability, and totally sealed and absolutely maintenance-free operation. The primary goal of metal hydride research for use in battery electrodes has been a cell capacity higher than that presently available with conventional Ni-Cd technology. A novel metal hydride consisting of Y, Zr, Mn, Fe, Co, V and Cr: YxZr1−xMnmFenCopVoCrq (m+n+o+p+q=2) is shown to give a higher electrochemical capacity. The electrochemical properties, such as electrode potential, reversible electrochemical capacity and diffusion coefficient as a function of state of charge in electrodes, are investigated in order to evaluate their suitability of the material as an electrode. The reversible electrochemical capacity of the electrode is found to be in excess of 450 mAh/g. Hydrogen concentration is estimated as r = nH/nf.u. = 3.5. The process that occurs in the electrode during charge and discharge has been studied by cyclic voltammogram (CV) experiments, carried out at different sweep rates. It is found that at low sweep rates, the hydrogen concentration on the surface increases due to longer polarization and approaches a value that favors a metal hydride formation. The diffusion coefficients are also evaluated with respect to state of charge.