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191 results on '"Kwon, Nam Hee"'

8. Uncertainty Evaluation for the Quantification of Urinary Amphetamine and 4-Hydroxyamphetamine Using Liquid Chromatography–Tandem Mass Spectrometry: Comparison of the Guide to the Expression of Uncertainty in Measurement Approach and the Monte Carlo Method with R

Author

Kim, Seon Yeong, primary, Shin, Dong Won, additional, Hyun, Jihye, additional, Kwon, Nam Hee, additional, Cheong, Jae Chul, additional, Paeng, Ki-Jung, additional, Lee, Jooyoung, additional, and Kim, Jin Young, additional

Published
2023
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13. Preparation of carbon nitride nanotubes with P-doping and their photocatalytic properties for hydrogen evolution

Author

Jang, Dawoon, primary, Lee, Suyeon, additional, Kwon, Nam Hee, additional, Kim, Taehoon, additional, Park, Sangjoon, additional, Jang, Kyung Yeon, additional, Yoon, Eojin, additional, Choi, Seungjoo, additional, Han, Juheon, additional, Lee, Tae-Woo, additional, Kim, Jeongho, additional, Hwang, Seong-Ju, additional, and Park, Sungjin, additional

Published
2023
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14. Defect-Regulated Two-Dimensional Superlattice of Holey g-C3N4–TiO2Nanohybrids: Contrasting Influence of Vacancy Content on Hybridization Impact and Photocatalyst Performance

Author

Kwon, Nam Hee, Park, Jihye, Jin, Xiaoyan, Kim, Se-Jun, Kim, Hyungjun, and Hwang, Seong-Ju

Abstract

Defect engineering provides an effective way to explore efficient nanostructured catalysts. Herein, we synthesize defect-regulated two-dimensional superlattices comprising interstratified holey g-C3N4and TiO2monolayers with tailorable interfacial coupling. Using this interfacial-coupling-controlled hybrid system, a strong interdependence among vacancy content, performance, and interfacial coupling was elucidated, offering key insights for the design of high-performance catalysts. The defect-optimized g-C3N4–TiO2superlattice exhibited higher photocatalytic activity toward visible-light-induced N2fixation (∼1.06 mmol g–1h–1) than defect-unoptimized and disorderly assembled g-C3N4–TiO2homologues. The high photocatalytic performance of g-C3N4–TiO2was attributed to the hybridization-induced defect creation, facilitated hydrogenation of adsorbed nitrogen, and improvement in N2adsorption and charge transport. A comparison of the defect-dependent photocatalytic activity of g-C3N4, g-C3N4nanosheets, and g-C3N4–TiO2revealed the presence of optimal defect content for improving photocatalytic performance and the continuous increase of hybridization impact with the defect content. Sophisticated mutual influence among defect, electronic coupling, and photocatalytic ability underscores the importance of defect fine control in exploring high-performance hybrid photocatalysts. Along with the DFT calculation, the excellent photocatalyst performance of defect-optimized g-C3N4–TiO2can be ascribed to the promotion of the uphill *N hydrogenation step as well as to enhancement of N2adsorption, charge transfer kinetics, and mass transports.

Published
2023
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18. Preparation of Carbon Nitride Nanotubes with P-Doping and Their Photocatalytic Properties for Hydrogen Evolution

Author

Jang, Dawoon, primary, Lee, Suyeon, additional, Kwon, Nam Hee, additional, Kim, Taehoon, additional, Park, Sangjoon, additional, Jang, Kyung Yeon, additional, Yoon, Eojin, additional, Choi, Seungjoo, additional, Han, Juheon, additional, Lee, Tae-Woo, additional, Kim, Jeongho, additional, Hwang, Seong-Ju, additional, and Park, Sungjin, additional

Published
2022
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23. Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C electrode material for lithium ion batteries exhibiting faster kinetics and enhanced stability

Author

Srout, Mohammed, Kwon, Nam Hee, Ben Youcef, Hicham, Semlal, Nawal, Fromm, Katharina M., and Saadoune, Ismael

Abstract

Natrium super ionic conductor (NASICON) materials providing attractive properties such as high ionic conductivity and good structural stability are considered as very promising materials for use as electrodes for lithium- and sodium-ion batteries. Herein, a new high-performance electrode material, Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C, was synthesized via the sol–gel method and was electrochemically tested as an anode for lithium ion batteries, providing enhanced electrochemical performance as a result of nickel substitution into the lithium site in the LiTi2(PO4)3 family of materials. The synthesized material showed good ionic conductivity, excellent structural stability, stable long-term cycling performance, and improved high rate cycling performance compared to LiTi2(PO4)3. The Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C electrode delivered reversible capacities of about 93 and 68% of its theoretical one at current rates of 0.1 C (6.42 mA·g–1) after 100 cycles and 5 C (320.93 mA·g–1) after 1000 cycles, respectively. Theoretically, three Li+ ions can be inserted into the vacancies of the Li0.5Ni0.5Ti1.5Fe0.5(PO4)3/C structure. However, when the electrode is discharged to 0.5 V, more than three Li+ ions are inserted into the NASICON structure, leading to its structural transformation, and thus to an irreversible electrochemical behavior after the first discharge process.

Published
2020

25. A nano-rattle SnO2@carbon composite anode material for high-energy Li-ion batteries by melt diffusion impregnation

Author

Maharajan, Sivarajakumar, Kwon, Nam Hee, Brodard, Pierre, Fromm, Katharina M., Maharajan, Sivarajakumar, Kwon, Nam Hee, Brodard, Pierre, and Fromm, Katharina M.

Abstract

The huge volume expansion in Sn-based alloy anode materials (up to 360%) leads to a dramatic mechanical stress and breaking of particles, resulting in the loss of conductivity and thereby capacity fading. To overcome this issue, SnO2@C nano- rattle composites based on < 10 nm SnO2 nanoparticles in and on porous amorphous carbon spheres were synthesized using a silica template and tin melting diffusion method. Such SnO2@C nano-rattle composite electrodes provided two electrochemical processes: a partially reversible process of the SnO2 reduction to metallic Sn at 0.8 V vs. Li+/Li and a reversible process of alloying/dealloying of LixSny at 0.5 V vs. Li+/Li. Good performance could be achieved by controlling the particle sizes of SnO2 and carbon, the pore size of carbon, and the distribution of SnO2 nanoparticles on the carbon shells. Finally, the areal capacity of SnO2@C prepared by the melt diffusion process was increased due to the higher loading of SnO2 nanoparticles into the hollow carbon spheres, as compared with Sn impregnation by a reducing agent.

Published
2020

26. New Ni0.5Ti2 (PO4)3@C NASICON-type electrode material with high rate capability performance for lithium-ion batteries: Synthesis and electrochemical properties

Author

Srout, Mohammed, Kwon, Nam Hee, Luo, Wen, Züttel, Andreas, Fromm, Katharina M., and Saadoune, Ismael

Abstract

Ni0.5Ti2(PO4)3/C NASICON‐type phosphate is introduced as a new anode material for lithium‐ion batteries (LIBs). Ni0.5Ti2(PO4)3/C was synthesized through the sol–gel route and delivered some remarkable electrochemical performances. Specifically, the Ni0.5Ti2(PO4)3/C electrode demonstrates a high rate capability performance and delivers high reversible capacities ranging from 130 mAh g−1 to about 111 mAh g−1 at current rates ranging from 0.1 C to 5 C in the voltage window of 1.85–3 V (vs. Li+/Li). In the same voltage range, the material reaches an initial capacity of 105 mAh g−1 with a capacity retention of about 82 % after 1000 cycles at the high current rate of 10 C. The electrodes are also tested in the wider voltage range of 0.5–3 V (vs. Li+/Li) and show good reversibility and rate capability performance. Moreover, the Ni0.5Ti2(PO4)3/C electrodes enable fast Li+ diffusion (in the order of 10−13 cm2 s−1) compared with other NASICON‐type materials. As a result, a first discharge capacity of 480 mAh g−1 is reached.

Published
2019

34. Multilayer Conductive Hybrid Nanosheets as Versatile Hybridization Matrices for Optimizing the Defect Structure, Structural Ordering, and Energy‐Functionality of Nanostructured Materials.

Author

Kwon, Nam Hee, Jin, Xiaoyan, Kim, Se‐Jun, Kim, Hyungjun, and Hwang, Seong‐Ju

Subjects
*NANOSTRUCTURED materials, *MULTILAYERED thin films, *SUPERCAPACITOR electrodes, *CERAMIC capacitors, *DENSITY functional theory, *METALLIC oxides
Abstract

The hybridization of conductive nanospecies has garnered significant research interest because of its high efficacy in improving the diverse functionalities of nanostructured materials. In this study, a novel synthetic strategy is developed to optimize the defect structure, structural ordering, and energy‐related functionality of nanostructured‐materials by employing a multilayer multicomponent two‐dimenstional (2D) graphene/metal oxide/graphene nanosheet (NS) as a versatile hybridization matrix. The hybridization of the robust trilayer, polydiallyldiammonium (PDDA)‐anchored reduced‐graphene oxide (prGO)/metal oxide/prGO NS effectively enhance the structural ordering and porosity of the hybridized MoS2/MnO2 NS through suppression of defect formation and tight stacking. In comparison with monolayer rGO/RuO2 NS‐based homologs, the 2D superlattice trilayer prGO/RuO2/prGO NS hybrids deliver better functionalities as a hydrogen evolution electrocatalyst and as a supercapacitor electrode, demonstrating the merits of hybridization with multilayer NSs. The advantages of using multilayer multicomponent conductive NSs as hybridization matrices arise from the enhancement of charge and mass transport through the layer flattening or defect suppression of the hybridized NSs and the increase in porosity, as evidenced by density functional theory calculations. Finally, the universal utility of multilayer NSs is confirmed by investigating the strong effect of the stacking order on the electrocatalytic functionality of MoS2/rGO/RuO2 films fabricated through layer‐by‐layer deposition. [ABSTRACT FROM AUTHOR]

Published
2022
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36. Surface modifications of positive-electrode materials for lithium ion batteries

Author

Kwon, Nam Hee, Conder, Joanna, Srout, Mohammed, Fromm, Katharina M., Kwon, Nam Hee, Conder, Joanna, Srout, Mohammed, and Fromm, Katharina M.

Abstract

Lithium ion batteries are typically based on one of three positive-electrode materials, namely layered oxides, olivine- and spinel-type materials. The structure of any of them is 'resistant' to electrochemical cycling, and thus, often requires modification/post- treatment to improve a certain property, for example, structural stability, ionic and/or electronic conductivity. This review provides an overview of different examples of coatings and surface modifications used for the positive-electrode materials as well as various characterization techniques often chosen to confirm/detect the introduced changes. It also assesses the electrochemical success of the surface-modified positive-electrode materials, thereby highlighting remaining challenges and pitfalls.

Published
2019

37. Early-stage sustainability evaluation of nanoscale cathode materials for lithium ion batteries

Author

Hischier, Roland, Kwon, Nam Hee, Brog, Jean?Pierre, and Fromm, Katharina M.

Abstract

Results of an early-stage sustainability evaluation of two development strategies for new nanoscale cathode materials for Li-ion batteries are reported: (i) a new production pathway for an existing material (LiCoO2) and (ii) a new nanomaterial (LiMnPO4). Nano-LiCoO2 was synthesized by a single-source precursor route at a low temperature with a short reaction time, which results in a smaller grain size and, thereby, a better diffusivity for Li ions. Nano-LiMnPO4 was synthesized by a wet chemical method. The sustainability potential of these materials was then investigated (at the laboratory and pilot production scales). The results show that the environmental impact of nano-LiMnPO4 is lower than that of the other examined nanomaterial by several factors regardless of the indicator used for comparison. In contrast to commercial cathode materials, this new material shows, particularly on an energy and capacity basis, results of the same order of magnitude as those of lithium manganese oxide (LiMn2O4) and only slightly higher values than those for lithium iron phosphate (LiFePO4); values that are clearly lower than those for high-temperature LiCoO2.

Published
2018

46. Characteristics and properties of nano-LiCoO2 synthesized by pre-organized single source precursors: Li-ion diffusivity, electrochemistry and biological assessment

Author

Brog, Jean?Pierre, Crochet, Aurélien, Seydoux, Joël, Clift, Martin J. D., Baichette, Benoît, Maharajan, Sivarajakumar, Barosova, Hana, Brodard, Pierre, Spodaryk, Mariana, Züttel, Andreas, Rothen?Rutishauser, Barbara, Kwon, Nam Hee, Fromm, Katharina M., Brog, Jean?Pierre, Crochet, Aurélien, Seydoux, Joël, Clift, Martin J. D., Baichette, Benoît, Maharajan, Sivarajakumar, Barosova, Hana, Brodard, Pierre, Spodaryk, Mariana, Züttel, Andreas, Rothen?Rutishauser, Barbara, Kwon, Nam Hee, and Fromm, Katharina M.

Abstract

LiCoO₂ is one of the most used cathode materials in Li-ion batteries. Its conventional synthesis requires high temperature (>800 °C) and long heating time (>24 h) to obtain the micronscale rhombohedral layered high-temperature phase of LiCoO₂ (HT-LCO). Nanoscale HT-LCO is of interest to improve the battery performance as the lithium (Li⁺) ion pathway is expected to be shorter in nanoparticles as compared to micron sized ones. Since batteries typically get recycled, the exposure to nanoparticles during this process needs to be evaluated.

Published
2017

48. Characteristics and properties of nano-LiCoO2 synthesized by pre-organized single source precursors: Li-ion diffusivity, electrochemistry and biological assessment

Author

Brog, Jean-Pierre, primary, Crochet, Aurélien, additional, Seydoux, Joël, additional, Clift, Martin J. D., additional, Baichette, Benoît, additional, Maharajan, Sivarajakumar, additional, Barosova, Hana, additional, Brodard, Pierre, additional, Spodaryk, Mariana, additional, Züttel, Andreas, additional, Rothen-Rutishauser, Barbara, additional, Kwon, Nam Hee, additional, and Fromm, Katharina M., additional

Published
2017
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50. New Ni0.5Ti2 (PO4)3@C NASICON‐type Electrode Material with High Rate Capability Performance for Lithium‐Ion Batteries: Synthesis and Electrochemical Properties.

Author

Srout, Mohammed, Kwon, Nam Hee, Luo, Wen, Züttel, Andreas, Fromm, Katharina M., and Saadoune, Ismael

Subjects
LITHIUM-ion batteries, ALKALINE batteries, ELECTRODES, MATERIALS, ANODES, DIFFUSION
Abstract

Ni0.5Ti2(PO4)3/C NASICON‐type phosphate is introduced as a new anode material for lithium‐ion batteries (LIBs). Ni0.5Ti2(PO4)3/C was synthesized through the sol–gel route and delivered some remarkable electrochemical performances. Specifically, the Ni0.5Ti2(PO4)3/C electrode demonstrates a high rate capability performance and delivers high reversible capacities ranging from 130 mAh g−1 to about 111 mAh g−1 at current rates ranging from 0.1 C to 5 C in the voltage window of 1.85–3 V (vs. Li+/Li). In the same voltage range, the material reaches an initial capacity of 105 mAh g−1 with a capacity retention of about 82 % after 1000 cycles at the high current rate of 10 C. The electrodes are also tested in the wider voltage range of 0.5–3 V (vs. Li+/Li) and show good reversibility and rate capability performance. Moreover, the Ni0.5Ti2(PO4)3/C electrodes enable fast Li+ diffusion (in the order of 10−13 cm2 s−1) compared with other NASICON‐type materials. As a result, a first discharge capacity of 480 mAh g−1 is reached. [ABSTRACT FROM AUTHOR]

Published
2019
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