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434 results on '"Roh, Kwang Chul"'

11. New Approach to Determine the Quality of Graphene

Author

Kim, Soo-Whan, Kim, Hyun-Kyung, Lee, Sunghun, Lee, Kyujoon, Han, Joong Tark, Kim, Kwang-Bum, Roh, Kwang Chul, and Jung, Myung-Hwa

Subjects
Condensed Matter - Materials Science
Abstract

The reduction of graphene oxide is one of the most facile methods to fabricate a large amount of graphene and the reduction rate of graphene oxide is related with the quality of synthesized graphene for its possible application. The reduction rate is usually determined by using various spectroscopy measurements such as Raman spectroscopy, Fourier transform infrared spectroscopy, and X-ray photoelectron spectroscopy. Here we propose that the magnetic data can be used as a means of determining the quality of graphene oxide (GO) and reduced graphene oxide (RGO) by the investigation of close relation between magnetic moment and chemical bonding state. Our experimental findings and previous theoretical studies suggest that hydroxyl functional groups in GO mainly contribute to Langevin paramagnetism, carboxyl functional groups in RGO1 act as the source for Pauli paramagnetism, and sp2 bonding state in RGO2 plays a major role on the diamagnetism. Especially in terms of mass production, the magnetic data is useful for decomposing the chemical bonding electronic states in graphene-like samples and judging their quality., Comment: 17 pages, 4 figures

Published
2017

41. Giant-miscanthus-derived activated carbon and its application to lithium sulfur batteries

Author

Lim, Geon Hae, Chae, Ji Su, Cha, Young-Lok, Kang, Yun Chan, and Roh, Kwang Chul

Abstract

Giant miscanthus (GM) is an Asian grass that can produce biomass in high yields per land area. It can be used as a cathode material in lithium sulfur (Li/S) batteries. Giant-miscanthus-derived activated carbon (GMAC) is prepared via carbonization of GM followed by KOH activation. It is prepared with a large amount of KOH, and thus contained more defects but had a highly porous structure and graphitic cluster lattice. GMAC has a large specific surface area of 3327 m2/g and a large total pore volume of 1.86 cm3/g. The pore volume served as a storage space for the retention of polysulfides, thereby inhibiting the shuttle effect. When a GMAC–sulfur composite cathode is tested in a Li/S battery, an initial discharge capacity of 1148 mAh/g can be attained at 0.1 C. In a cyclic charge–discharge experiment at 1 C, discharge capacities of 529 mAh/g and 248 mAh/g are observed in the first and 200th cycles, respectively.

Published
2024
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50. Electrolyte ions-matching hierarchically porous biochar electrodes with an extended potential window for next-generation supercapacitors.

Author

Rama Raju, Ganji Seeta, Kondrat, Svyatoslav, Chodankar, Nilesh R., Hwang, Seung-Kyu, Lee, Jeong Han, Long, Teng, Pavitra, Eluri, Patil, Swati J., Ranjith, Kugalur Shanmugam, Rao, M. V. Basaveswara, Wu, Peng, Roh, Kwang Chul, Huh, Yun Suk, and Han, Young-Kyu

Abstract

Engineering high-performance carbonaceous electrode materials from earth-abundant biomass has attracted substantial attention for its applicability in next-generation supercapacitors (SCs). However, these materials exhibit low specific energy due to the dominance of mesopores and a limited potential window. To overcome these shortcomings, herein, we synthesize Miscanthus sinensis (silver grass)-derived hierarchically-porous activated carbons (SHACs) via pyrolysis, carbonization, and KOH activation. We test the SHAC electrodes with different electrolytes, showing how an electrolyte–electrode pair can be tuned to boost energy and power densities. Owing to the synergetic effect of the size-balanced proportion of micropores matched with the size of electrolyte ions, in KOH electrolyte, the SHAC electrode produces a high specific capacitance (592 F g−1) while, simultaneously, providing faster charging compared to Na2SO4 electrolyte. We rationalize these findings with molecular dynamics simulations, demonstrating the avoidance of power-density trade-off, typical for microporous SCs. Upon adding K3Fe(CN)6 redox species to KOH electrolyte (hybrid electrolyte), capacitance increases 2.53 fold (380 to 963 F g−1 at 5 A g−1) due to the synergy of capacitive and faradaic energy storage mechanisms. In the hybrid electrolyte, a SHAC electrode-embedded symmetric SC (SSC) offers a high cycling stability (97%) with 1.6 V wide operational voltage and permits energy storage and power density higher than those reported so far for aqueous electrolyte-based SSCs and asymmetric SCs. In addition, these SSCs provide long-lasting operational capabilities that are useful for driving various portable electronic devices. The obtained results demonstrate a feasible methodology to utilize the maximum available surface area of carbonaceous materials for electrochemical energy storage applications. [ABSTRACT FROM AUTHOR]

Published
2023
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