Ick-Jun Kim

Characterization of Graphene Nanosheets as Electrode Material and Their Performances for Electric Double-Layer Capacitors

In this work, graphene nanosheets were prepared using the Hummers-Offeman method. We prepared the resultant graphene electrode with kneading type. The prepared graphene nanosheets were characterized by X-ray diffraction, scanning electron microscopy with energy dispersive X-ray analysis, transmission electron microscopy, Fourier transform infrared spectroscopy instrument and Raman spectra. Finally, the electrochemical performances of graphene nanosheets in an electrolyte solution of tetraethylammonium tetrafluoroborate ((C2H5)4NBF4, TEABF4) in propylene carbonate (C4H6O3, PC) were examined.

FABRICATION OF TiNi/PZT HETEROSTRUCTURE FILMS FOR SMART SYSTEMS

Korea Electrotechnology Research Institute, 28-1 Sungju-dong, Changwon, 641-120, Korea(Received July 7, 2000)(Accepted August 9, 2000)Keywords: Shape memory; Ferroelectricity; Multilayer; Interface diffusion; Nucleation and growth1. IntroductionPiezoelectric materials and shape memory alloys (SMA) are widely used for actuator and sensorapplications [1,2]. It is well known that piezoelectric materials produce an electric field when the stressis applied, while it shows deformation when the electric field is applied. The response time ofpiezoelectricity is relatively fast, but the displacement of that is relatively small comparing to the otheractuactors. Shape memory alloys, on the other hand, can produce a large force-displacement duringmartensite-to-austenite transformation. However, the response time of shape memory effect is slowcomparing to that of piezoelectricity, because the shape memory kinetics are controlled by the thermaldiffusivity.Combination of piezoelectric materials with shape memory alloys and formation of the heterostruc-ture are expected to fabricate the advanced materials which show integrated function of piezoelectricityand shape memory property with keeping the function of each material [3,4]. If the heterostructure ofshape memory (TiNi) film and ferroelectric film is heated at the martensite-austenite transformationtemperature, the large force-displacement occurred in the TiNi film layer is supposed to cause thechange of electric field in the ferroelectric film layer. Therefore, the self detection of the displacementcan be performed by monitoring the electromotive force, and the self detection function seems to be theintegration of sensing and actuating function.In order to obtain the smart material, it is necessary to design the heterostructure film without loseingthe functions of each other by means of chemical interaction at the interface. The PZT films wereprepared by sol-gel process, and the TiNi films were deposited on PZT films heated at elevatedtemperatures. On growing the heterostructures, lowering the crystallization temperature of TiNi filmplays an important role in achieving the heterostructure without inter-diffusion. In this study, wedescribe the depositing process of heterostructures. In conjunction with the heterostructures, loweringthe crystallization temperature of TiNi film was also investigated in term of the surface morpology, andthe ferroelectric properties of the PZT layer were measured.2. Exprimental ProcedureTo prepare the piezoelectric film layer, commercially supplied PZT(52/48) precursor solutions wereused. (Kanto Chemical Co.) Partially hydrolyzed 0.5 M precursors were deposited onto Pt/Ti/SiO

CVD grown graphene/CNT composite as additive material to improve the performance of electric double layer capacitors (EDLCs)

In this work, large area graphene-carbon nanotube (G-CNT) composite as additive material for EDLC performance was grown on copper foil at low temperature (500 °C) and at atmospheric pressure by using chemical vapor deposition (CVD). The growth state was characterized by field emission scanning electron microscope (FESEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. EDLC electrodes based on high surface area activated carbon (YP50F) and G-CNT were then fabricated by a facile step. Coin-type EDLC cells with two symmetrical carbon electrodes were assembled using the prepared carbon materials. The electrochemical performance of G-CNT based eletrodes were examined in an electrolyte solution of tetraethylammonium tetrafluoroborate ((C2H5)4NBF4, TEABF4) in propylene carbonate (C4H6O3, PC) and measured by galvanostatic charge/discharge and cyclic voltammetry methods.

Anomalous reheating behavior of SiCp/Al composite with high volume fraction reinforcement

The reheating behavior of 50 vol.% SiCp/Al squeeze casting composite was investigated at temperatures ranging from 600°C to 900°C using XRD and SEM techniques from the microstructural point of view. It was found that SiCp/Al composite could hold its original shape while being reheated at temperatures elevated even far above the melting temperature of pure Al. The high volume fraction of SiC reinforcement, which would restrict the fluidity of molten Al matrix and the reconfiguration of SiC particles during the reheating of SiCp/Al composite, was thought to be responsible for the “remelting resistance” of the SiCp/Al composite. The extent of the reaction between the SiC particles and molten Al was found to increase with increased reheating temperature. From the viewpoint of controlling the formation of aluminum carbide, reheating temperature either for recycling or for remelting processing of the SiCp/Al composite, a temperature lower than 750°C would be better. Despite its being unfavorable to remelting or recycling processing, the remelting resistance of the SiCp/Al composite with high volume fraction reinforcement is attractive for thermal function and high temperature applications.

Novel preparation of expanded nano-graphene-based electrodes for EDLC and their improved electrochemical performance

ABSTRACT The electrode raw materials in this work were composed of expanded nano-graphene (ENG)-based active carbon (YP50F) named YEG as an active material; Super-P carbon black (SPB) as an electric conductor; and styrene–butadiene rubber (SBR), sodium salt of carboxymethyl cellulose (CMC), and polytetrafluoroethylene ((C2F4)n, PTFE) as mixed binder materials. We characterized the prepared electrodes by X-ray diffraction, scanning electron microscopy, and Raman spectroscopic techniques. Finally, we examined the electrochemical performances of carbon materials in an electrolyte solution of tetraethylammonium tetrafluoroborate ((C2H5)4NBF4, TEABF4) in propylene carbonate (C4H6O3, PC). The specific capacitance remains the same for smaller values of YEG in the composite electrodes. These results also provide evidence of the optimum loading of ENG in future graphene-based EDLCs.

Enhanced specific capacitance of modified needle cokes by controlling oxidation treatment

The electric double-layer performance of needle cokes can be affected by the morphology of structures. Hence, we introduce modified needle cokes by using simple oxidation treatment. The degree of graphitization with high specific capacitance is controlled by acid and heat treatment. The active sites of cokes are increased with increasing oxidation time. Dilute nitric acid (HNO3) and sodium chlorate (NaClO3) are used for the activation of cokes. In this case, the interlayer distance is dramatically increased from 3.5 to 8.9 A. The specific capacitances are 33 F g−1 and 30 F ml−1, respectively, on a two-electrode system with a potential range of 0–2.5 V. The behaviors of double-layer capacitance are demonstrated by the charge–discharge process and the morphologies of modified needle cokes are analyzed by XRD, FE-SEM, BET and elemental analysis.

Effect of Acid / Heat Treatment on Electric Double Layer Performance of Needle Cokes

In this study, a needle coke was oxidized in a mixture of dilute nitric acid and sodium chlorate () solutions and followed by heat treatment. The samples were analyzed with using XRD, FESEM, elemental analyzer, BET, and Raman spectroscopy. Double layer capacitance was measured with the charge and discharge measurements. The consisting layers of the needle coke were expanded to single phase showing only (001) diffraction peak by the acid treatment for 24 hours. The oxidized coke returned to a graphite structure appearing (002) peak after heat treatment above . The structure returned could be more easily accessible to the ions by the first charge, and improve the double layer capacitance at the second charge. The two-electorde cell from acid treated coke and heat treatment exhibited the maximum capacitances of 32.1 F/g and 29.5 F/ml at the potential of .

Preparation and Electrochemical Performance of Carbon-PTFE Electrode for Electric Double Layer Capacitor

This work describes the effect of the number of roll pressing and the composition of carbon black on the electric and mechanical properties of carbon-PTFE electrode, in which composition is MSP20 : carbon black :

Electric and Mechanical Properties of CMC+PTFE Binary Binder Electrode for Electric Double Layer Capacitor

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Tunneling magnetoresistance in sintered Fe3O4 samples diluted with Fe and α-Fe2O3

This work describes the effect of electrode binder on the characteristics of electric double layer capacitor. Among carboxymethylcellulose (CMC), Polyvinylpyrrolidone (PVP), Polyvinyl Alcohol (PVA), and Polyvinylidene Fluoride (PVDF), the unit cell using CMC showed good rate capability at current densities between 2.5 mA/～100 mA/. However, CMC as a binder is incongruent, because the electrode bound with CMC is rigid and easy to crack during a press and winding process for fabrication of capacitor. The unit cell capacitor using the electrode bound with binary binder composed of CMC and Polytetrafluoroethylene (PTFE), especially in composition CMC : PTFE