Jang Myoun Ko

Carbon Nanotube/RuO2 nanocomposite electrodes for supercapacitors

Electrochemical characteristics of electrodes for supercapacitors built from RuO 2 /maltiwalled carbon nanotube (CNT) nanocomposites have been investigated. Capacitances have been estimated by cyclic voltammetry at different scan rates from 5-50 mV/s. Electrostatic charge storage as well as pseudofaradaic reactions of RuO 2 nanoparticles have been affected by the surface functionality of CNTs due to the increased hydrophilicity. Such hydrophilicity enables easy access of the solvated ions to the electrode/electrolyte interface, which increases faradaic reaction site number of RuO 2 nanoparticles. The specific capacitance of RuO 2 /pristine CNT nanocomposites based on the combined mass was about 70 F/g (RuO 2 : 13 wt % loading). and the specific capacitance based on the mass of RuO 2 was 500 F/g. However, the specific capacitance of RuO 2 /hydrophilic CNT nanocomposites based on the combined mass was about 120 F/g (RuO 2 : 13 wt % loading), and the specific capacitance based on the mass of RuO 2 was about 900 F/g.

Characterization of poly(vinylidenefluoride-co-hexafluoropropylene)-based polymer electrolyte filled with rutile TiO2 nanoparticles

Various amounts of nanoscale rutile TiO2 particle are used as fillers in the preparation of poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)-based porous polymer electrolytes. Physical, electrochemical and transport properties of the electrolyte films are investigated in terms of surface morphology, thermal and crystalline properties, swelling behavior after absorbing electrolyte solution, chemical and electrochemical stabilities, ionic conductivity, and compatibility with lithium electrode. Contrary to reported inorganic fillers showing the maximum content lower than 50 wt.%, the self-supporting polymer electrolyte films can be obtained even when using higher content of 70 wt.% rutile TiO2 nanoparticles. The physical and electrochemical properties of polymer membrane are highly improved by the addition of TiO2 nanoparticles as good dispersion of fillers, low liquid uptake but adequate ionic conductivity, excellent electrochemical stability, and stabilized interfacial resistance with lithium electrode. An emphasis should be put on the fact that the sufficient ionic conductivity obtained is led by the liquid medium within nano-pores as well as effective ion transport supported by rutile TiO2. As a result, the sample with 30–40 wt.% rutile TiO2 is confirmed as the best polymer electrolyte for rechargeable lithium batteries.

Preparation and electrochemcial characteristics of plasticized polymer electrolytes based upon a P(VdF-co-HFP)/PVAc blend

Abstract Polymer electrolytes based on the mixture of the blended polymer matrix (P(VdF-co-HFP)(Kynar 2801)/poly(vinyl acetate)(PVAc)) and the liquid electrolyte(EC/PC/1M LiClO 4 ) were prepared by solution casting. Ionic conductivity, interfacial stability with the lithium electrode, and electrochemical stability window of the polymer electrolytes were investigated by varying the PVAc content in the matrix polymer. The ionic conductivity of the plasticized polymer electrolyte slightly decreased with the PVAc content. The ionic conductivity of the polymer electrolyte based on the Kynar 2801/PVAc (7/3, w/w) blend was 2.3×10 −3 S cm −1 at 25°C. Interfacial stability between the polymer electrolyte and the lithium electrode was enhanced by blending PVAc with the Kynar 2801. The polymer electrolyte based on the Kynar 2801/PVAc (7/3, w/w) blend was electrochemically stable up to 5.0 V.

Electrochemical performances of lithium-ion cells prepared with polyethylene oxide-coated separators

Poly(ethylene oxide) (PEO)-coated separators were prepared by coating PEO onto a microporous polyethylene (PE) separators. Highly conductive electrolytes were prepared by soaking them in an electrolyte solution. The uptake of the electrolyte solution and the ionic conductivity of the PEO-coated separator (PCS) after soaking in LiBF4–ethylene carbonate (EC)/dimethyl carbonate (DMC) were measured to be 76% and 1.0×10−3S/cm, respectively. With these PCSs, lithium-ion cells composed of mesocarbon microbead (MCMB) anode and LiCoO2 cathode were assembled, and their electrochemical performances were evaluated.

A polymer humidity sensor

Abstract Polypyrrole doped with dodecylsulfate ion on electrochemical polymerization of pyrrole keeps the anion in it on reduction of the polymer in an aqueous solution. The free anion on reduction of the polymer attracts a cation to form a salt in the polymer. An attempt was made to use polypyrrole as a sensing material in measurement of humidity. The gold covered electrode was constructed by employing a photo-resist method and the ionic conductivity of the reduced polypyrrole changes from 2 × 10 kΩ·cm to 3 × 103 kΩ·cm depending on humidity.

Highly conductive polymer electrolytes supported by microporous membrane

Highly conductive polymer electrolytes supported by a microporous separator were prepared and characterized. These polymer electrolytes were prepared by coating poly(ethylene oxide) (PEO) and poly(ethylene glycol dimethacrylate) (PEGDMA) onto a microporous polyethylene membrane, and soaking them in an electrolyte solution. The relative weight ratio of PEO and PEGDMA coated on the microporous membrane proved to play a critical role in determining uptake of an electrolyte solution and ionic conductivity. The electrolyte optimized in this work displayed a high ionic conductivity and electrochemical stability, exhibiting no solvent leakage. An encapsulation of electrolyte solution within the porous membrane diminished the passivation of lithium electrodes. With these electrolytes, lithium-ion polymer cells composed of a carbon anode and LiCoO2 cathode were assembled, and their electrochemical performances were evaluated.

Electrical conductivity change of polyaniline–dodecyl benzene sulfonic acid complex with temperature

Polyaniline–dodecylbenzene sulfonic acid (PAn–DBSA) complex was thermally treated and its conductivity and structure change were investigated. The conductivity increased linearly from 1.1 × 10−4 to 3.0 × 10−1 S/cm on thermal heating until 140°C, but decayed above 200°C. The increase was caused by an additional thermal doping resulting from an increasing mobility of undoped dopants. After the thermal doping, the formation of the layered structure of PAn–DBSA is made. The decrease was caused by the thermal decomposition of dopants. The conductivity changes at a high temperature was strongly dependent on the nature of the dopant. The results were confirmed by means of X-ray patterns and Fourier transform infrared spectra obtained in the heating and cooling processes of polyaniline.

Electrodeposited Ni1 − x Co x Nanocrystalline Thin Films Structure–Property Relationships

Electrodeposition of nanocrystalline Ni and Ni 1-x Co x thin films from chloride baths was systematically investigated by varying the electrodeposition parameters including electrolyte composition (i.e., Co 2+ ion concentration), additive (i.e., saccharin), solution pH, and current density. Their effects on the film growth mechanism, film composition, residual stress, microstructure, grain size, and surface morphology were studied. Ni 1-x Co x thin films electrodeposited from the baths without the addition of saccharin always showed tensile stress mode (145-367 MPa) with varying Co 2+ ion concentration, solution pH, and current density. In the presence of saccharin, the Ni 1-x CO x thin films showed either tensile stress or compressive stress mode, depending on the electrodeposition conditions. Especially, it was observed from a cross-sectional TEM observation that Ni thin film electrodeposited from the bath containing saccharin exhibited the formation of an amorphous Ni layer (about 300 nm thick) at the initial stage of the film growth. Also, Ni 1-x Co x thin films electrodeposited from the bath with/without the addition of saccharin showed the formation of the interface phase layer (about 10-110 nm thick), which has the chemical composition of 50 atom % Ni and 50 atom % Co.

SYNTHESIS AND ELECTRO-OPTICAL PROPERTIES OF POLY(2-ETHYNYLPYRIDINIUMTOSYLATE) HAVING PROPAGYL SIDE CHAIN

Novel conjugated ionic polymer was prepared by the polymerization of 2-ethynylpyridine with propargyl tosylate in refluxing methyl alcohol. The polymerization proceeded well in homogeneous manner to give a relatively high yield of polymer. The resulting poly(2-ethynylpyridinium tosylate) having propargyl side chain [poly(EPT-P)] were hygroscopic and soluble in water, methyl alcohol, DMF, and DMSO. The inherent viscosities of the polymers were in the range of 0.08-0.29dL/g. Instrumental analyses using NMR, IR, and UV-visible spectroscopies and elemental analyses indicated that the resulting poly(EPT-P) have a conjugated ionic polymer backbone carrying N-propargyl-2-pyridinium tosylate. Thermal and electro-optical properties of the polymers were also studied.

Synthesis and electrochemical properties of a polynorbornene derivative containing a carbazole moiety

SummaryA new polymer, poly {5-[[(6-N-carbazoylhexyl)oxy]methyl]-2-norbornene} [Poly (NCHN)], was synthesized by ring-opening metathesis polymerization (ROMP) with various transition metal catalyst systems. The structure of the poly (NCHN) was analyzed by NMR, IR, and UV-vis spectroscopy. The electrochemical properties of the poly (NCHN) were characterized by cyclic voltammetric technique. From the cyclic voltammetric results it was concluded that the carbazole units in side chain of the polymer were oxidized and coupled irreversibly to form dicarbazyls. The redox kinetics was mainly controlled by both electron transfer and ClO4- diffusion processes preserving the electro-neutrality of the polymer.