• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.847-852
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• 2019

In this study, the effect of additives on the performance of aqueous organic redox flow battery (AORFB) using quinoxaline and ferrocyanide as active materials in alkaline supporting electrolyte is investigated. Quinoxaline shows the lowest redox potential (-0.97 V) in KOH supporting electrolyte, while when quinoxaline and ferrocyanide are used as the target active materials, the cell voltage of this redox combination is 1.3 V. When the single cell tests of AORFBs using 0.1 M active materials in 1 M KCl supporting electrolyte and Nafion 117 membrane are implemented, it does not work properly because of the side reaction of quinoxaline. To reduce or prevent the side reaction of quinoxaline, the two types of additives are considered. They are the potassium sulfate as electrophile additive and potassium iodide as nucleophilie additive. Of them, when the single cell tests of AORFBs using potassium iodide as additive dissolved in quinoxaline solution are performed, the capacity loss rate is reduced to $0.21Ah{\cdot}L^{-1}per\;cycle$ and it is better than that of the single cell test of AORFB operated without additive ($0.29Ah{\cdot}L^{-1}per\;cycle$).

• New Physics: Sae Mulli
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• v.68 no.12
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• pp.1315-1323
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• 2018

We studied the carbonization due to the annealing condition of waste coffee powder for application as an active anode material for lithium-ion batteries (LIBs). The coffee powder used as an active anode material for LIBs was obtained from coffee beans, not from a coffee shells. The waste coffee powder was dried in air and heat-treated in an $Ar/H_2$ atmosphere to obtain a pore-forming activated carbon powder. The specific capacity of the sample annealed at $700^{\circ}C$ was still 303 mAh/g after 1000 cycles at a current density of 1000 mA/g and with a coulombic efficiency of over 99.5%. The number of pores and the pore size of the waste coffee powder were increased due to chemical treatment with KOH, which had the some effect as an increased specific surface area. The waste coffee powder is considered to be a very promising active anode material because of both its excellent electrochemical properties due to enhanced carrier conduction and its being a cost effective resource for use in LIBs.

• Applied Chemistry for Engineering
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• v.31 no.6
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• pp.639-645
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• 2020

Among the components of redox flow battery (RFB), the electrode serves as a diffusion layer of an electrolyte and a path for electrons and also is a major component that directly affects the RFB performance. In this paper, chloric/sulfuric mixed acidwas used as a supporting electrolyte in RFB system with Fe2+/Fe3+ and V2+/V3+ as redox couple. The optimum electrode and activation temperature were suggested by comparing the capacity, coulombic efficiency and energy efficiency according to the electrode type and activation temperature. In the RFB single cell evaluation using 5 types of carbon electrodes used in the experiments, all of them showed close to the theoretical capacity to retain the reliability of the evaluation results. GFD4EA showed relatively excellent energy efficiency and charge/discharge capacity. In order to investigate the electrochemical performance according to the activation temperature, GFD4EA electrode was activated by heat treatment at different temperatures of 400, 450, 500, 600 and 700 ℃ under an air atmosphere. Changes in physical properties before and after the activation were observed using electrode mass retention, scanning electron microscope (SEM), XPS analysis, and electrochemical performance was compared by conducting RFB single evaluation using electrodes activated at each temperature given above.

• Journal of the Korean Electrochemical Society
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• v.17 no.2
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• pp.94-102
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• 2014

Cation exchange membrane (Nafion) was modified to reduce the vanadium ion permeation through the membrane and to increase the vanadium redox flow battery (VRB) system performance by coating the graphene oxide (GO) which has nano-plate like morphology. Modified membrane properties were studied by measuring the ion exchange capacity (I.E.C), water uptake and proton conductivity. The thickness of the coated layer on the surface of the Nafion membrane was observed as $0.93{\mu}m$ by SEM. Proton conductivity and vanadium ion permeability of the modified membrane were decreased to 27% and 25% compared to that of the commercial Nafion membrane respectively. VRB single cell performance test was performed to compare the system performance of the VRB applied with commercial Nafion membrane and modified membrane. VRB system applied with modified membrane showed higher coulombic efficiency and energy efficiency than the VRB system applied with the commercial Nafion membrane due to the reduction of the vanadium ion permeation. From these result, we could suggest that the membrane modification by coating the GO on the surface of the Nafion membrane could be one of the promising strategies to reduce the vanadium ion permeation and to increase the VRB system performance effectively.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.9 no.5
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• pp.1045-1051
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• 2005

We developed an orofacial pains diagnosis/therapy system which can enlarge a therapy effect through a new stimulation. Contrary to its established method, this therapy system(DDTS-1) is a treating method which absorbs a surplus ion charge- the cause of an outbreak of a pain-of the human body using a capacitor. Absorbing a surplus ion charge of the human body with effect, it obtained optimal parameters which is control signal to control charging/discharging a capacitor to be 6Hz, and capacitance to be $0.1\~0.33{\mu}F.$ Through clinical demonstration, experimented on among patients-namely dental pain patients, joint disorders patients, and trigeminal neuralgia patients to verification of system. In result, an EAST stimulater had a very low change of abnormal potential against normal potential before/after being placed under medical care. DDTS-1 showed obvious differences that two potentials are one and the same potential or one potential is similar to the other one. DDTS-1 comparing with EAST showed the remedial value of the comparative advantage in all the medical treatment of pains. Therefore, stimulation of DDTS-1 is more effective than the existing electric stimulation. We verified its validity of ion charge absorption in the human body using capacitor which presented the present thesis. That is, we verified theoretical adequacy of control action in a pain, and its efficiency as well as confidence.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.14 no.1
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• pp.56-69
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• 2021

In this paper, the PV system with a link to the commercial system needs some advantages like small capacity, high power factor, high reliability, low harmonic output, maximum power operation of solar cell, and low cost, etc. as well as the properties of inverter. To transfer the PV energy of photovoltaic power generation system to the system and load, it requires PCS in both directions. The purpose of this paper is to confirm the stable power supply through the load leveling by presenting the PCS considering ESS of photovoltaic power generation. In order to achieve these purpose, 5 step process of operation mode algorithm were used according to the solar insolation amount and load capacity and the controller for charging/ discharging control was designed. For bidirectional and effective energy transfer, the bidirectional converter and battery at DC-link stage were connected and the DC-link voltage and inverter output voltage through the interactive inverter were controlled. In order to prove the validity of the suggested system, the simulation using PSIM was performed and were reviewed for its validity and stability. The 3[kW] PCS was manufactured and its test was conducted in order to check this situation. In addition, the system characteristics suggested through the test results was verified and the PCS system presented in this study was excellent and stronger than that of before system.

• Journal of the Korean Applied Science and Technology
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• v.38 no.3
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• pp.903-913
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• 2021

Three-type PVC membranes denoted by AEM-1, AEM-2, and AEM-3 with a cross-linked anion-exchange group were prepared by substitution reaction of PVC with triethyldiamine (TEDA), 1,4-dimethylpiperazine (DMP), and 1,4-bis(imidazol-1-ylmethyl)benzene (BIB) in cyclohexanone, respectively. We confirmed the successful preparation of the AEM-1, AEM-2, and AEM-3 via ionic conductivity (S/cm), water uptake (%), contact angle, ion-exchange capacity (m_eq/g), thermal properties, SEM and XPS analysis, respectively. The electrochemical capacitor experiments using PVC membrane with cross-linked anion-exchange group in organic electrolytes were performed. The prepared AEM-1, AEM-2 AEM-3 have a good stability by charge and discharge performance in organic electrolyte. As a result, the AEM-2 and AEM-3 membrane based on PVC prepared by the solvent casting method after substituent reaction is suitable for the use as a separator in organic electrochemical capacitor (supercapacitor).

• Korean Chemical Engineering Research
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• v.55 no.5
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• pp.593-599
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• 2017

In order to enhance ultra battery performances, the electrochemical characteristics of nano Pb/AC anode composite was investigated. Through nano Pb adsorption onto activated carbon, nano Pb/AC was synthesized and it was washed under vacuum process. The prepared anode materials was analysed by SEM, BET and EDS. The specific surface area and average pore size of nano Pb/AC composite were $1740m^2/g$ and 1.95 nm, respectively. The negative electrode of ultra battery was prepared by nano Pb/AC dip coating on lead plate. The electrochemical performances of ultra battery were studied using $PbO_2$ (the positive electrode) and prepared nano Pb/AC composite (the negative electrode) pair. Also the electrochemical behaviors of ultra battery were investigated by charge/discharge, cyclic voltammetry, impedance and rate capability tests in 5 M $H_2SO_4$ electrolyte. The initial capacity and cycling performance of the present nano Pb/AC ultra battery were improved with respect to the lead battery and the AC-coated lead battery. These experimental results indicate that the proper addition of nano Pb/AC into the negative electrode can improve the discharge capacity and the long term cycle stability and remarkably suppress the hydrogen evolution reaction on the negative electrode.

• Applied Chemistry for Engineering
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• v.9 no.2
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• pp.220-225
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• 1998

The spinel structured $LiMn_2O_4$ was prepared from $Li_2CO_3$ and $MnO_2$ by calcination at various temperatures in the range of $750{\sim}900^{\circ}C$. It was found that the most suitable cubic structure of $LiMn_2O_4$ was obtained by heating at $850^{\circ}C$ for 12 hrs. However, in the calcination at $900^{\circ}C$, $Mn^{4+}$ of 0.06M was changed to $Mn^{+3}$ by the oxygen loss, so that it has been shown that the formula has changed to $LiMn_2O_{3.97}$. This phenomena were in agreement with the Jahn-Teller distortion by the increment of $Mn^{+3}$ ion on the octahedral sites of the spinel structured $LiMn_2O_4$. The results showed that after 15 charge/discharge cycles in the voltage range from 3.5V to 4.3V versus Li/$Li^+$ with a current density of $0.25mA/cm^2$, the spinel structured $LiMn_2O_4$ that was prepared at $900^{\circ}C$ showed a lower discharge capacity, 82~50 mAh/g, while the $LiMn_2O_4$, prepared at $850^{\circ}C$, showed the discharge capacity of 102~64 mAh/g.

• Korean Chemical Engineering Research
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• v.55 no.3
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• pp.307-312
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• 2017

In this study, the electrochemical performance of surface modified carbon using the PFO (pyrolyzed fuel oil) was investigated by chemical activation with KOH and $K_2CO_3$. PFO was heat treated at $390{\sim}400^{\circ}C$ for 1~3h to prepared the pitch. Three carbon precursors (pitch) prepared by the thermal reaction were 3903 (at $390^{\circ}C$ for 3h), 4001(at $400^{\circ}C$ for 1h) and 4002 (at $400^{\circ}C$ for 2h). Also, the effect of chemical activation catalysts and mixing time on the development of porosity during carbonization was investigated. The prepared carbon was analyzed by BET and FE-SEM. It was shown that chemical activation with KOH could be successfully used to develop carbon with specific surface area ($3.12m^2/g$) and mean pore size (22 nm). The electrochemical characteristics of modified carbon as the anode were investigated by constant current charge/discharge, cyclic voltammetry and electrochemical impedance tests. The coin cell using pitch (4002) modified by KOH has better initial capacity (318 mAh/g) than that of other pitch coin cells. Also, this prepared carbon anode appeared a high initial efficiency of 80% and the retention rate capability of 2C/0.1 C was 92%. It is found that modified carbon anode showed improved cycling and rate capacity performance.