• Polymer(Korea)
• /
• v.34 no.4
• /
• pp.357-362
• /
• 2010

Poly(ethyleneglycol diacrylate)(PEGDA) or 2-ethylhexyl acrylate(2EHA)-based gel polymer electrolytes(GPEs) which have a solid content in the range of 8～54 wt% were synthesized and their ionic conductivity and electrochemical properties were measured at room temperature. It was observed that the ionic conductivity over $1\times10^{-3}$ S/cm was obtained in a homogeneous PEGDA-based GPE with 21 wt% of solid content. However the electrochemical stability of the GPE was lower than that of a liquid electrolyte. The presence of AIBN initiator which can produce a N2 gas during polymerization process might be the reason of this low oxidation decomposition potential. As an alternative, benzoyl peroxide was used as an initiator and GPE with enhanced electrochemical stability was obtained. Finally, the formation of stable solid electrolyte interphase on a graphite anode was evidenced by cyclic voltammetry measurement.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.67 no.12
• /
• pp.1641-1647
• /
• 2018

In this paper, we describe a portable potentiostat which is capable of cyclic voltammetry(CV) and amperometry for electrochemical dissolved oxygen sensor. In addition, this portable potentiostat can also transmit the measured data wirelessly to android devices such as smart phone, tablet, etc. through Bluetooth. The potentiostat system consists of three parts; a voltage generator circuit which is controlled by Arduino nano and 12-bit DAC(digital to analog converter) to generate necessary electric potential for operating the electrochemical sensor, an oxidation/reduction current measurement circuit, and a Bluetooth module to transmit data wirelessly to an android device. Once measurements are carried out with the android application, the measured data is transmitted to the android device via Bluetooth and displayed using the android app. in real time. In this paper, we report the measured reduction current with a fabricated dissolved oxygen sensor in both saturated-oxygen state and zero-oxygen states. The results of the developed portable potentiostat system are in good agreement with those of the commercial portable potentiostat (${\mu}stat200$, Dropsens inc.). The measured peak reduction currents using the developed potentiostat and the commercial ${\mu}stat200$ potentiostat were $-0.755{\mu}A$ and $-0.724{\mu}A$, respectively. The reduction currents measured at zero-oxygen state were $-0.005{\mu}A$ and $-0.004{\mu}A$. The discrepancy between those two systems seems very small, which implies successful development of a portable and wireless potentionstat.

• Korean Chemical Engineering Research
• /
• v.57 no.1
• /
• pp.5-10
• /
• 2019

In this study, electrochemical characteristics of artificial graphite coated with petroleum pitch using solvent method as anode material of lithium ion battery were investigated. As the solvent, n-hexane, toluene, tetrahydrofuran and quinoline were used. The surface of the prepared anode material was analyzed by SEM and TEM. Also the electrochemical performances of the prepared anode materials were performed by constant current first charge/discharge, cycle, cyclic voltammetry and impedance tests in the electrolyte of $LiPF_6$ dissolved inorganic solvents (EC:DEC=1:1 vol%). The coating thickness of the prepared graphite was about 100-500 nm and the graphite coated with THF solvent had a smoother surface than that using other solvents. It was found that pitch-coated graphite (THF) show the low initial irreversible capacity (51 mAh/g), the high discharge capacity (360 mAh/g) and coulombic efficiency (99%).

• Electronic Materials Letters
• /
• v.14 no.6
• /
• pp.755-765
• /
• 2018

In situ nitrogen doped hard carbon nanotubes (NHCNT) were fabricated by pyrolyzing tubular nitrogen doped conjugated microporous polymer. KOH activated NHCNT (K-NHCNT) were also prepared to improve their porous structure. XRD, SEM, TEM, EDS, XPS, Raman spectra, $N_2$ adsorption-desorption, galvanostatic charging-discharge, cyclic voltammetry and EIS were used to characterize the structure and performance of NHCNT and K-NHCNT. XRD and Raman spectra reveal K-NHCNT own a more disorder carbon. SEM indicate that the diameters of K-NHCNT are smaller than that of NHCNT. TEM and EDS further indicate that K-NHCNT are hollow carbon nanotubes with nitrogen uniformly distributed. $N_2$ adsorption-desorption analysis reveals that K-NHCNT have an ultra high specific surface area of $1787.37m^2g^{-1}$, which is much larger than that of NHCNT ($531.98m^2g^{-1}$). K-NHCNT delivers a high reversible capacity of $918mAh\;g^{-1}$ at $0.6A\;g^{-1}$. Even after 350 times cycling, the capacity of K-NHCNT cycled after 350 cycles at $0.6A\;g^{-1}$ is still as high as $591.6mAh\;g^{-1}$. Such outstanding electrochemical performance of the K-NHCNT are clearly attributed by its superior characters, which have great advantages over those commercial available carbon nanotubes ($200-450mAh\;g^{-1}$) not only for its desired electrochemical performance but also for its easily and scaling-up preparation.

• Korean Chemical Engineering Research
• /
• v.57 no.5
• /
• pp.606-610
• /
• 2019

In this study, we demonstrated that the nonenzymatic glucose sensor based on the flexible carbon fiber bundle electrode with BDD nanocomposites (CF-BDD electrode). As a nano seeding method for the deposition of BDD on flexible carbon fiber, electrostatic self-assembly technique was employed. Surface morphology of BDD coated carbon fiber electrode was observed by scanning electron microscopy. And the electrochemical characteristics were investigated by cyclic voltammetry, electrochemical impedance spectroscopy and chronoamperometry. This CF-BDD electrode exhibited a large surface area, a direct electron transfer between the redox species and the electrode surface and a high catalytic activity, resulting in a wider linear range (3.75~50 mM), a faster response time (within 3 s) and a higher sensitivity (388.8 nA/mM) in comparison to a bare CF electrode. As a durable and flexible electrochemical sensing electrode, this brand new CF-BDD scheme has promising advantages on various electrochemical and wearable sensor applications.

• Korean Chemical Engineering Research
• /
• v.57 no.5
• /
• pp.672-678
• /
• 2019

The electrochemical properties of pitch-coated natural graphite(NG) were investigated as an anode for lithium-ion batteries. The anode materials were prepared by heat-treatment of mixture of NG and petroleum pitch at $1000^{\circ}C$. The pitches with various softening points were used as carbon precursor. The physical properties of anode materials were analyzed by TGA, SEM, PSA and BET. As the softening point increased, the thickness of the coating layer increased and the specific surface area decreased. The electrochemical performances were investigated by initial charge/discharge efficiency, cycle stability, cyclic voltammetry, rate performance and electrochemical impedance spectroscopy. The carbon-coated NG using pitch with softening points of $250^{\circ}C$ showed an initial discharge capacity of 361 mAh/g and a coulombic efficiency of 92.6%. Also, the rate performance(5 C/0.2 C) was 1.6 times higher than that of NG, and it had a capacity retention (90%) after 50 cycles at 0.5 C.

• Korean Chemical Engineering Research
• /
• v.59 no.3
• /
• pp.326-332
• /
• 2021

In this study, a spherical carbon composite material containing nano-silicon was synthesized using hydrothermal synthesis, and coated with petroleum pitch to prepare an anode material to investigate the electrochemical characteristics. Hydrothermal synthesis was performed by varying molar concentration, and the pitch was coated using THF as an organic solvent to prepare a composite material. The physical properties of anode materials were analyzed using SEM, EDS, XRD and TGA, and the electrochemical performances were investigated by cycle, C-rate, cyclic voltammetry and electrochemical impedance tests in 1.0 M LiPF₆ electrolyte (EC : DMC : EMC = 1 : 1 : 1 vol%). The pitch-coated silicon/carbon composite (Pitch@Si/C-1.5) with sucrose of 1.5 M showed a spherical shape. In addition, a high initial capacity of 1756 mAh/g, a capacity retention ratio of 82% after 50 cycles, and an excellent rate characteristic of 81% at 2 C/0.1 C were confirmed.

• Applied Chemistry for Engineering
• /
• v.31 no.6
• /
• pp.603-606
• /
• 2020

A hydrophilic alkaline room temperature ionic liquid electrolyte (RT-IL) carrying hydroxide ion as an anion and 1-benzyl-3-butylimidazolium as a cation was synthesized. Electrochemical, physical and structural properties of the synthesized RT-IL were characterized using cyclic voltammetry, ionic conductivity, viscosity, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), FT-IR, and 1H-NMR measurements. High ionic conductivity and low viscosity characteristics comparable to 0.1 M KCl electrolyte solution were achieved for the RT-IL in addition to a wide electrochemical potential window of about 4.4 V. The results indicate that the RT-IL is promising for future applications as an alternative electrolyte to energy and environmental research fields.

• Bulletin of the Korean Chemical Society
• /
• v.14 no.2
• /
• pp.195-200
• /
• 1993

The neutral, reduced, and oxidized 2,2-trans isomers of $Rh_2(ap)_4$ (ap=2-anilinopyridinate) were investigated with respect to dioxygen binding in $CH_2Cl_2$ containing 0.1 M tetrabutyl-ammonium perchlorate. $Rh_2(ap)_4$ binds dioxygen in nonaqueous media and forms a $Rh^{II}Rh^{III}$ superoxide complex, $Rh_2(ap)_4(O_2)$. This neutral species was isolated and is characterized by UV-visible and IR spectroscopy, mass spectrometry and cyclic voltammetry. It can be reduced by one electron at $E_{1/2}$ = -0.45 V vs. SCE in $CH_2Cl_2$ and gives ${[Rh_2(ap)_4(O_2)]}^-$ as demonstrated by the ESR spectrum of a frozen solution taken after controlled potential reduction. The superoxide ion in ${[Rh_2(ap)_4(O_2)]}^-$ is axially bound to one of the two rhodium ions, both of which are in a +2 oxidation state. $Rh_2(ap)_4(O_2)$ can also be stepwise oxidized in two one-electron transfer steps at $E_{1/2}$ = 0.21 V and 0.85 V vs. SCE in $CH_2Cl_2$ and gives ${[Rh_2(ap)_4(O_2)]}^+$ followed by ${[Rh_2(ap)_4(O_2)]}^{2+}$. ESR spectra demonstrate that the singly oxidized complex is best described as ${[Rh^{II}Rh^{III}(ap)_4(O_2)]}^+$ where the odd electron is delocalized on both of the two rhodium ions and the axial ligand is molecular oxygen.

• Korean Journal of Materials Research
• /
• v.31 no.3
• /
• pp.115-121
• /
• 2021

MnO2 can be potentially utilized as an electrode material for redox capacitors. The deposition of MnO2 with poor electrical conductivity onto porous carbons supplies them with additional conductive paths; as a result, the capacitance of the electrical double layer formed on the porous carbon surface can be utilized together with the redox capacitance of MnO2. However, the obtained composites are not generally suitable for industrial production because they require the use of expensive porous carbons and/or inefficient fabrication methods. Thus, to develop an effective preparation procedure of the composite, a suitable structure of porous carbons must be determined. In this study, MnO2/C composites have been prepared from activated carbon gels with various pore sizes, and their electrical properties are investigated via cyclic voltammetry. In particular, mesoporous carbons with a pore size of around 20 nm form a composite with a relatively low capacitance (98 F/g-composite) and poor rate performance despite the moderate redox capacitance obtained for MnO2 (313 F/g-MnO2). On the other hand, using macro-porous carbons with a pore size of around 60 nm increases the MnO2 redox capacitance (399 F/g-MnO2) as well as the capacitance and rate performance of the entire material (203 F/g-composite). The obtained results can be used in the industrial manufacturing of MnO2/C composites for supercapacitor electrodes from the commercially available porous carbons.