• Journal of Electrochemical Science and Technology
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• 제12권1호
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• pp.112-125
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• 2021

The new emerging "High entropy materials" attract the attention of the scientific society because of their simpler structure and spectacular applications in many fields. A novel nanocrystalline high entropy (Be,Mg,Ca,Sr,Zn,Ni)3O4 oxide has been successfully synthesized through mechanochemical treatment followed by sintering and air quenching. The present research work focuses on the possibility of single-phase formation in the aforementioned high entropy oxide despite the great difference in the atomic sizes of reactant alkaline earth and 3d transition metal oxides. Structural properties of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide were explored by confirmation of its single-phase Fd-3m spinel structure by x-ray diffraction (XRD). Further, nanocrystalline nature and morphology were analyzed by scanning electron microscopy (SEM). Among thermal properties, thermogravimetric analysis (TGA) revealed that the (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is thermally stable up to a temperature of 1200℃. Whereas phase evolution in (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide before and after sintering was analyzed through differential scanning calorimetry (DSC). Electrochemical studies of (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide consists of a comparison of thermodynamic and kinetic parameters of water and hydrazine hydrate oxidation. Values of activation energy for water oxidation (9.31 kJ mol-1) and hydrazine hydrate oxidation (13.93 kJ mol-1) reveal that (Be,Mg,Ca,Sr,Zn,Ni)3O4 high entropy oxide is catalytically more active towards water oxidation as compared to that of hydrazine hydrate oxidation. Electrochemical impedance spectroscopy is also performed to get insight into the kinetics of both types of reactions.

• Nuclear Engineering and Technology
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• 제54권3호
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• pp.965-974
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• 2022

Platinum anodes are widely used for metal oxides reduction in LiCl-Li₂O, however high-cost and low-corrosion resistance hinder their implementation. NiO-Li₂O ceramics is an alternative corrosion resistant anode material. Anode processes on platinum and NiO-Li₂O ceramics were studied in (80 mol.%) LiCl-(20mol.%)KCl and (80 mol.%)LiCl-(20 mol.%)KCl-Li₂O melts by cyclic voltammetry, potentiostatic and galvanostatic electrolysis. Experiments performed in the LiCl-KCl melt without Li₂O illustrate that a Pt anode dissolution causes the Pt²⁺ ions formation at 3.14 V and 550℃ and at 3.04 V and 650℃. A two-stage Pt oxidation was observed in the melts with the Li₂O at 2.40 ÷ 2.43 V, which resulted in the Li₂PtO₃ formation. Oxygen current efficiency of the Pt anode at 2.8 V and 650℃ reached about 96%. The anode process on the NiO-Li₂O electrode in the LiCl-KCl melt without Li₂O proceeds at the potentials more positive than 3.1 V and results in the electrochemical decomposition of ceramic electrode to NiO and O₂. Oxygen current efficiency on NiO-Li₂O is close to 100%. The NiO-Li₂O ceramic anode demonstrated good electrochemical characteristics during the galvanostatic electrolysis at 0.25 A/cm² for 35 h and may be successfully used for pyrochemical treating of spent nuclear fuel.

• Korean Chemical Engineering Research
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• 제59권2호
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• pp.159-164
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• 2021

부착형(attachable) 타입의 웨어러블 디바이스 적용을 위한 패브릭(fabric)이나 텍스처(textiles) 타입의 고성능 전극 소재 개발에 대한 필요성이 부각되고 있다. 본 연구에서는 유연 전극 소재로 탄소나노튜브 섬유(CNT fibers)를 응용하고자, CNT fibers의 전기화학적 특성과 이를 적용한 비효소적 글루코스 센싱 성능을 확인하였다. CNT fibers의 표면 구조는 주사전자 현미경(SEM)을 이용하여 분석하였으며, 전기화학적 특성 및 센싱 성능 분석은 시간대전류법와 순환전압 전류법, 전기화학 임피던스 분석법을 이용하여 수행되었다. CNT fibers 전극은 낮은 capacitive current와 산화-환원 화학종과 전극 계면 간의 효율적인 direct electron transfer에 의한 우수한 electrochemical activity 등 향상된 전기화학적 특성으로 인해 높은 감도와 넓은 선형 농도 범위, 그리고 낮은 검출 한계 등 우수한 센싱 특성을 보였다. 따라서, 본 연구는 CNT fibers 기반의 고성능 유연 전극 소재 개발을 위한 기초 연구로 활용될 수 있을 것으로 기대된다.

• Journal of Electrochemical Science and Technology
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• 제13권4호
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• pp.438-452
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• 2022

For cuboid and ellipsoid crystallites of LiFePO₄ powders, by X-ray diffraction (XRD) and microscopic (TEM) studies, it is possible to determine the anisotropic parameters of the crystallite size distribution functions. These parameters were used to describe the cathode rate capability within the model of averaging the diffusion coefficient D over the length of the crystallite columns along the [010] direction. A LiFePO₄ powder was chosen for testing the developed model, consisting of big cuboid and small ellipsoid crystallites (close to them). When analyzing the parts of big and small rate capabilities, the fitting values D = 2.1 and 0.3 nm²/s were obtained for cuboids and ellipsoids, respectively. When analyzing the results of cyclic voltammetry using the Randles-Sevcik equation and the total area of projections of electrode crystallites on their (010) plane, slightly different values were obtained, D = 0.9 ± 0.15 and 0.5 ± 0.15 nm²/s, respectively. We believe that these inconsistencies can be considered quite acceptable, since both methods of determining D have obvious sources of error. However, the developed method has a clearly lower systematic error due to the ability to actually take into account the shape and statistics of crystallites, and it is also useful for improving the accuracy of the Randles-Sevcik equation. It has also been demonstrated that the shape engineering of crystallites, among other tasks, can increase the cathode capacity by 15% by increasing their size correlation coefficients.

• 공업화학
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• 제33권2호
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• pp.210-215
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• 2022

표면의 전하 특성이 다른 두 가지 리그닌을 사용하여 이전 연구에서 제시된 간단한 방법인 용액상 화학적 중합을 이용하여 폴리피롤@리그닌(PPy@lignin) 및 폴리피롤@리그노설포네이트(PPy@lignosulfonate) 복합소재를 제조하였다. 폴리피롤은 두 가지 리그닌 표면에서 각각 성공적으로 중합되었으며, 얻어진 복합소재들은 주사전자현미경, 순환전압 전류법, 임피던스(impedance) 분석법 등을 이용하여 분석하였다. 이러한 결과들을 바탕으로, 리그닌의 종류가 달라도 복합재료들은 성공적으로 제조되는 것을 알 수 있었으며, 전기적 특성도 일정하게 유지되는 것으로 나타났다. 다만, 개별 리그닌의 표면 특성 차이로 나타나는 물성 차이가 존재함을 임피던스 분석으로 판단할 수 있었다. 나아가, 두 가지 복합소재들을 아가로즈(agarose) 젤(gel)에 투입하여 전도성 젤을 형성하고 이 젤들의 특성들을 역시 순환전압전류법으로 살펴보았으며, 전기전도도를 측정하여 제시하였다. 리그닌의 전기절연성에도 불구하고 전도성 젤이 전기전도도를 포함한 전기적 특성을 유지하는 것을 알 수 있었다. 이는 전도성 젤의 활용이 가능하다는 점을 의미한다.

• 한국재료학회지
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• 제32권5호
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• pp.243-248
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• 2022

This study demonstrates a different approach method to fabricate antimony selenide (Sb₂Se₃) thin-films for the solar cell applications. As-deposited Sb₂Se₃ thin-films are fabricated via electrodeposition route and, subsequently, annealed in the temperature range of 230 ~ 310℃. Cyclic voltammetry is performed to investigate the electrochemical behavior of the Sb and Se ions. The deposition potential of the Sb₂Se₃ thin films is determined to be -0.6 V vs. Ag/AgCl (in 1 M KCl), where the stoichiometric composition of Sb₂Se₃ appeared. It is found that the crystal orientations of Sb₂Se₃ thin-films are largely dependent on the annealing temperature. At an annealing temperature of 250 ℃, the Sb₂Se₃ thin-film grew most along the c-axis [(211) and/or (221)] direction, which resulted in the smooth movement of carriers, thereby increasing the carrier collection probability. Therefore, the solar cell using Sb₂Se₃ thin-film annealed at 250 ℃ exhibited significant enhancement in J_SC of 10.03 mA/cm² and a highest conversion efficiency of 0.821 % because of the preferred orientation of the Sb₂Se₃ thin film.

• Journal of Electrochemical Science and Technology
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• 제14권3호
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• pp.252-261
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• 2023

Glucose detection is particularly important for clinical diagnosis and personal prevention and control. Herein, the smartphone-based amperometric glucose sensors were constructed using the NiS/CuS nanorods (NRs) as sensing electrodes. The NiS/CuS NRs were prepared through a facile hydrothermal process accompanied by the subsequent vulcanization treatment. The morphological and structural properties of NiS/CuS NRs were characterized with SEM, EDS, XRD, and XPS. Electrochemical measurements including cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy display that NiS/CuS NRs can act as highly efficient electrocatalyst for glucose detection. The NiS/CuS NRs electrodes present a wide detection range of 1-8000 µM for glucose sensing with the sensitivity of 956.38 µA·mM^-1·cm^-2. The detection limit was 0.35 µM (S/N=3). When employed in smartphone-based glucose sensing device, they also display a high sensitivity of 738.09 µA·mM^-1·cm^-2 and low detection limit of 1.67 µM. Moreover, the smartphone-based glucose sensing device also presents favorable feasibility in determination of glucose in serum samples with the recoveries ranging between 99.5 and 105.8%. The results may provide a promising viewpoint to design other new portable glucose sensors.

• Korean Chemical Engineering Research
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• 제61권1호
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• pp.52-57
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• 2023

본 연구는 고성능 유연 전극 소재 개발을 위한 기초 연구로, 유연 전극 소재의 성능을 향상시키기 위해 금속 산화물 CuO nanoparticles (CuO NPs)를 도입하여 탄소나노튜브 섬유(carbon nanotube fiber; CNT fiber) 표면 위에 전기화학적 증착시켜 CNT fiber/CuO NPs 전극을 합성하고, 이를 전기화학적 비효소 글루코스 센서에 적용하였다. 이 전극의 표면 및 elemental composition 분석은 주사전자 현미경(SEM)과 에너지분산형 분광분석법(EDS)을 이용하였으며, 전극의 전기화학적 특성 및 글루코스에 대한 센싱 성능은 순환전압 전류법(CV)과 전기화학 임피던스법(EIS), 시간대전류법(CA)을 통해 조사되었다. CNT fiber/CuO NPs 전극은 CNT fiber의 우수한 특성과 함께 CuO NPs 도입에 따른 약 2.6배의 유효 전극면적(active surface area) 증가 효과와 11배 정도의 향상된 전자전달(electron transfer) 특성 및 우수한 전기적 촉매 활성(electrocatalytic activity) 덕분에 CNT fiber 유연 기반 전극의 글루코스 검출에 대한 성능이 개선되었다. 따라서, 본 연구를 기반으로 다양한 나노구조체를 활용한 고성능 유연 전극 소재 개발이 기대된다.

• Journal of Electrochemical Science and Technology
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• 제13권2호
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• pp.177-185
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• 2022

Electrochemical properties of LiMn₂O₄ cathode were investigated in three types of Zn-containing electrolytes: lithium-zinc sulfate electrolyte (1M ZnSO₄ / 2M Li₂SO₄), zinc sulfate electrolyte (2MZnSO₄) and lithium-zinc-manganese sulfate electrolyte (1MZnSO₄ / 2MLi₂SO₄ / 0.1MMnSO₄). Cyclic voltammetry measurements demonstrated that LiMn₂O₄ is electrochemically inactive in pure ZnSO₄ electrolyte after initial oxidation. The effect of manganese (II) additive in the zinc-manganese sulfate electrolyte on the electrochemical performance was analyzed. The initial capacity of LiMn₂O₄ is higher in presence of MnSO₄ (140 mAh g^-1 in 1 M ZnSO₄ / 2 M Li₂SO₄ / 0.1 M MnSO₄ and 120 mAh g^-1 in 1 M ZnSO₄ / 2MLi₂SO₄). The capacity increase can be explained by the electrodeposition of MnO_x layer on the electrode surface. Structural characterization of postmortem electrodes with use of XRD and EDX analysis confirmed that partially formed in pure ZnSO₄ electrolyte Zn-containing phase leads to fast capacity fading which is probably related to blocked electroactive sites.

• 전기화학회지
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• 제8권1호
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• pp.17-23
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• 2005

$Bi_2O_3$를 첨가한 8M KOH용액에서 다결정 Ag전극의 전기화학적인 거동과 생성된 산화물들의 미세조직 변화를 분석하였다. $Bi_2O_3$를 첨가한 8M KOH용액에서 Ag 산화물뿐만 아니라 새로운 Ag-Bi-O화합물들이 생성되는 것을 알 수 있었다. Ag(I) 산화물 생성 전위 영역에서는 $Ag_2O$ 이외에, Ag-Bi-O 화합물이 핵 생성과 3D성장 과정에 의해서 생성되고, Ag(II)산화물 생성 전위 영역에서는 AgO뿐만 아니라 새로운 Ag-Bi-O화합물들이 핵 생성과 3D성장 과정에 의해서 생성되었다. Ag(I) 산화물 생성 전위에서 두 가지 형상의 Ag(I) 산화물이 생성되는 것을 SEM 조직에 의해 관찰하였다.