Publications by authors named "Ho Jung Hwang"

12 Publications

  • Page 1 of 1

Transparent Bendable Secondary Zinc-Air Batteries by Controlled Void Ionic Separators.

Sci Rep 2019 Feb 28;9(1):3175. Epub 2019 Feb 28.

Department of Chemical and Biomolecular Engineering, Yonsei University, 262 Seongsanno, Seodaemun-gu, Seoul, 120-749, South Korea.

First ever transparent bendable secondary zinc-air batteries were fabricated. Transparent stainless-steel mesh was utilized as the current collector for the electrodes due to its reliable mechanical stability and electrical conductivity. After which separate methods were used to apply the active redox species. For the preparation of the anode, zinc was loaded by an electroplating process to the mesh. For the cathode, catalyst ink solution was spray coated with an airbrush for desired dimensions. An alkaline gel electrolyte layer was used for the electrolyte. Microscale domain control of the materials becomes a crucial factor for fabricating transparent batteries. As for the presented cell, anionic exchange polymer layer has been uniquely incorporated on to the cathode mesh as the separator which becomes a key procedure in the fabrication process for obtaining the desired optical properties of the battery. The ionic resin is applied in a fashion where controlled voids exist between the openings of the grid which facilitates light passage while guaranteeing electrical insulation between the electrodes. Further analysis correlates the electrode dimensions to the transparency of the system. Recorded average light transmittance is 48.8% in the visible light region and exhibited a maximum power density of 9.77 mW/cm. The produced battery shows both transparent and flexible properties while maintaining a stable discharge/charge operation.
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http://dx.doi.org/10.1038/s41598-019-38552-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6395654PMC
February 2019

Selective Ion Transporting Polymerized Ionic Liquid Membrane Separator for Enhancing Cycle Stability and Durability in Secondary Zinc-Air Battery Systems.

ACS Appl Mater Interfaces 2016 Oct 23;8(39):26298-26308. Epub 2016 Sep 23.

New Energy and Battery Engineering, Yonsei University , 134 Shinchon-dong, Seodaemoon-ku, Seoul 120-749, Republic of Korea.

Rechargeable secondary zinc-air batteries with superior cyclic stability were developed using commercial polypropylene (PP) membrane coated with polymerized ionic liquid as separators. The anionic exchange polymer was synthesized copolymerizing 1-[(4-ethenylphenyl)methyl]-3-butylimidazolium hydroxide (EBIH) and butyl methacrylate (BMA) monomers by free radical polymerization for both functionality and structural integrity. The ionic liquid induced copolymer was coated on a commercially available PP membrane (Celguard 5550). The coat allows anionic transfer through the separator and minimizes the migration of zincate ions to the cathode compartment, which reduces electrolyte conductivity and may deteriorate catalytic activity by the formation of zinc oxide on the surface of the catalyst layer. Energy dispersive X-ray spectroscopy (EDS) data revealed the copolymer-coated separator showed less zinc element in the cathode, indicating lower zinc crossover through the membrane. Ion coupled plasma optical emission spectroscopy (ICP-OES) analysis confirmed over 96% of zincate ion crossover was reduced. In our charge/discharge setup, the constructed cell with the ionic liquid induced copolymer casted separator exhibited drastically improved durability as the battery life increased more than 281% compared to the pure commercial PP membrane. Electrochemical impedance spectroscopy (EIS) during the cycle process elucidated the premature failure of cells due to the zinc crossover for the untreated cell and revealed a substantial importance must be placed in zincate control.
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http://dx.doi.org/10.1021/acsami.6b07841DOI Listing
October 2016

Synthesis and application of hexagonal perovskite BaNiO3 with quadrivalent nickel under atmospheric and low-temperature conditions.

Chem Commun (Camb) 2016 Sep 29;52(71):10731-4. Epub 2016 Jul 29.

Department of Chemical and Bio-molecular Engineering, Yonsei University, 134 Shinchon-dong, Seodaemun-gu, Seoul, 120-749, Republic of Korea.

A hexagonal perovskite BaNiO3 with unusually high-valence nickel(iv) was synthesized under atmospheric and low-temperature conditions by an ethylenediamine-derived wet-chemical route. Secondary phases disappeared with increase in the pH value, and the single-phase BaNiO3 was successfully synthesized at pH 10. The specific surface area was ∼32 m(2) g(-1), which is significantly enhanced compared to the BaNiO3 (0.3 m(2) g(-1)) synthesized by flux-mediated crystal growth. The BaNiO3 was used as an oxygen-evolution reaction (OER) catalyst, and the specific mass activity was ∼5 times higher than that of the BaNiO3 synthesized by flux-mediated crystal growth. As a result, the ethylenediamine-derived sol-gel synthesis could be a simple technique to prepare crystalline compounds such as perovskites and spinels, with unusually high-valence transition metals.
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http://dx.doi.org/10.1039/c6cc05704gDOI Listing
September 2016

A New Family of Perovskite Catalysts for Oxygen-Evolution Reaction in Alkaline Media: BaNiO3 and BaNi(0.83)O(2.5).

J Am Chem Soc 2016 Mar 2;138(10):3541-7. Epub 2016 Mar 2.

Department of Chemical and Bio-molecular Engineering, Yonsei University , 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749, Republic of Korea.

Establishment of a sustainable energy society has been strong driving force to develop cost-effective and highly active catalysts for energy conversion and storage devices such as metal-air batteries and electrochemical water splitting systems. This is because the oxygen evolution reaction (OER), a vital reaction for the operation, is substantially sluggish even with precious metals-based catalysts. Here, we show for the first time that a hexagonal perovskite, BaNiO3, can be a highly functional catalyst for OER in alkaline media. We demonstrate that the BaNiO3 performs OER activity at least an order of magnitude higher than an IrO2 catalyst. Using integrated density functional theory calculations and experimental validations, we unveil that the underlying mechanism originates from structural transformation from BaNiO3 to BaNi(0.83)O(2.5) (Ba6Ni5O15) over the OER cycling process.
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http://dx.doi.org/10.1021/jacs.6b00036DOI Listing
March 2016

Comparison of resonance frequencies between normal and tangential vibration modes of graphene-nanoribbon-resonators.

J Nanosci Nanotechnol 2013 Dec;13(12):8095-100

Department of Electronic Engineering, Semyung University, Jecheon 390-711, Republic of Korea.

We investigate tunable graphene-nanoribbon (GNR)-resonators actuated in the tangential direction, and their properties are compared to those actuated in the normal direction, via classical molecular dynamics simulations. These GNR-resonators can be tuned both by the initial strain and the gate. The relationships between the frequency-versus-gate and the initial strain in this work are in good agreement with those in previous experimental works. With increasing initial strain, the resonance frequencies are greatly upshifted, whereas the tunable ranges in frequency are greatly decreased. The tunability in the dynamic operating range decreases with increasing initial strain. For very small strains, the GNR-resonators have large dynamic operating ranges in the normal vibration mode, and for large strains, the GNR-resonators have higher operating frequencies in the tangential vibration mode. The resonance frequencies are estimated by a classical continuum model, with tension acting on the GNR-resonators consisting of both initial tension by initial strain and induced tension by gate actuating.
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http://dx.doi.org/10.1166/jnn.2013.8193DOI Listing
December 2013

Study on electromigratively-telescoping carbon-nanotube-based reversible-tuner.

J Nanosci Nanotechnol 2011 Jul;11(7):6359-63

Department of Computer Engineering, Chungju National University, Chungju 380-702, Korea.

We conceptually investigated a carbon-nanotube-based tuner operated by the telescoping nanotube motion in a multi-walled carbon-nanotube induced by electromigration of an encapsulated nanoparticle. The telescoping lengths in the proposed carbon-nanotube-based tuner could be achieved from the electromigration phenomena of the nanoparticle embedded in the carbon nanotube. So the core part is the nanoparticle shuttle and a multi-walled carbon-nanotube with ultra-low interlayer friction. The tuning of this telescoping carbon-nanotube-based tuner is achieved from the electric current flow. The properties of operation were investigated via classical molecular dynamics simulations and then the parameters of the continuum model were then calibrated to fit the results of the molecular dynamics simulations. Since the effective boundary considered as the movable clamp affected the vibration of the telescoping nanotube, the calibrated Young's modulus of this work were lower than the those of the previous works. Presented tuners are controllable in a few nanometers, and their operations are robust and reliable.
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http://dx.doi.org/10.1166/jnn.2011.4467DOI Listing
July 2011

Molecular dynamics study of nano mass transfer in a vibrating cantilevered carbon-nanotube.

J Nanosci Nanotechnol 2011 Jul;11(7):5856-60

Department of Computer Engineering, Chungju National University, Chungju 380-702, Korea.

We investigate the nano mass transfer in an ultrahigh frequency carbon-nanotube-resonator encapsulating a nanocluster via classical molecular dynamics simulations. When the carbon-nanotube-resonator vibrated, the encapsulated copper nanocluster more rapidly approached the end of the cantilevered carbon-nanotube-resonator. Such phenomena were due to the migration of the encapsulated copper nanocluster due to the centrifugal force induced by the vibrating nanotube resonator. So the resonance frequency change could be time-dependently found. For the movable copper nanocluster in carbon nanotube resonator, the vibrational spectra when the copper nanocluster inside the carbon nanotube resonator rapidly settled at the capped edge were different from those obtained when the copper nanocluster continuously oscillated inside the carbon nanotube resonator. Such results showed that the frequency of the carbon-nanotube-resonator encapsulating the movable copper nanocluster could be adjusted by controlling the mean position of the oscillating copper nanocluster. The movable nanocluster inside a carbon-nanotube can be applied to a nanotube-based data storage media by sensing the position of the nanocluster.
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http://dx.doi.org/10.1166/jnn.2011.4461DOI Listing
July 2011

Linear nanomotor based on electromigration of a nanoparticle encapsulated in a carbon nanotube.

J Nanosci Nanotechnol 2011 Feb;11(2):1573-6

Department of Computer Engineering, Chungju National University, Chungju 380-702, Korea.

We investigated a linear nanomotor based on the telescoping carbon nanotube motion induced by electromigration of an encapsulated nanoparticle. The nanoparticle motion induced by the electric current makes the inner nanotube linearly telescope or retreat. Theoretical results using a kinetic Monte Carlo method were in good agreement with previous experiments. The telescoping speed of the linear nanomotor exponentially decreased with increasing mass of the inner nanotube.
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http://dx.doi.org/10.1166/jnn.2011.3390DOI Listing
February 2011

Resonant frequencies of cantilevered (8,8)(3,3) double-walled carbon nanotube Resonator with short outer wall.

J Nanosci Nanotechnol 2011 Jan;11(1):445-8

Department of Electronic Engineering, Semyung University, Jecheon 390-711, Korea.

Resonant frequencies of cantilevered (8,8)(3,3) double-walled carbon nanotube (DWCNT) resonators are investigated via classical molecular dynamics simulation. The interwall van der Walls forces as a nonlinear function had a great effect on noncoaxial vibration of DWCNT resonators. Bandwidths of DWCNT resonators with short outer walls were similar with each other irregardless to the structural difference. The frequency trends of DWCNT resonators with short outer wall were affected by the outer wall length. The vibration of the DWCNT resonator with short outer wall was very closely related to the vibration of the inner CNT in the stripped region.
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http://dx.doi.org/10.1166/jnn.2011.3170DOI Listing
January 2011

Molecular dynamics simulations of an inertia sensor with carbon nanotube oscillators.

J Nanosci Nanotechnol 2009 Dec;9(12):6943-7

Department of Computer Engineering, Chungju National University, Chungju 380-702, Korea.

We investigated a nanoscale inertia sensor based on telescoping carbon nanotubes (CNTs) using classical molecular dynamics simulations. The positions of the telescoping CNTs are controlled by the centrifugal forces exerted by the rotation platform and thus position shifts are determined by the capacitance between CNTs and the electrode, and the operating frequency of the CNT oscillator. This measurement system, tracking oscillations of the CNT oscillator, can be used as the sensor for numerous types of devices, such as motion detectors, accelerometers, and acoustic sensors.
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http://dx.doi.org/10.1166/jnn.2009.1617DOI Listing
December 2009

The frequency of cantilevered double-wall carbon nanotube resonators as a function of outer wall length.

J Phys Condens Matter 2009 Sep 24;21(38):385301. Epub 2009 Aug 24.

Department of Computer Engineering, Chungju National University, Chungju 380-702, Republic of Korea.

Analysis of vibrational characteristics of cantilevered double-walled carbon nanotube (DWCNT) resonators is carried out based on classical molecular dynamics simulation. Vibrational frequencies of DWCNTs are less than those of single-walled carbon nanotubes (SWCNTs) with the same length and the same diameter because of van der Waals intertube interaction. For DWCNTs with short outer walls, the resonance frequency initially increases with increasing outer nanotube length and then decreases after a peak, and thus the result can be modeled by a Gaussian distribution. The frequency of DWCNT resonators with short outer walls is a maximum when the length of the outer wall is about 72.5% of the length of the inner wall.
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http://dx.doi.org/10.1088/0953-8984/21/38/385301DOI Listing
September 2009

Molecular dynamics study of hypothetical silicon nanotubes using the Tersoff potential.

J Nanosci Nanotechnol 2002 Dec;2(6):687-91

Semiconductor Process and Device Laboratory, Department of Electronic Engineering, Institute of Technology and Science, Chung-Ang University, DongJak-Ku, Seoul 156-756, Korea.

We have performed classical molecular dynamics simulations for hypothetical silicon nanotubes using the Tersoff potential. Our investigation presented a systematic study about the thermal behavior of hypothetical silicon nanotubes and showed the difficulty in producing silicon nanotubes or graphitelike sheets. However, since the elastic energy per atom to curve the sheet into cylinders for silicon atoms is as low as that for carbon atoms, if graphitelike sheets of silicon are formed, the extra cost to produce the tubes is of a similar order to that in carbon. Through the investigations on the structure and properties of a double-wall silicon nanotube, we concluded that quasi-one-dimensional structures consisting of silicon atoms become nanowires rather than nanotubes in order to minimize the number of sp2 bonds.
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http://dx.doi.org/10.1166/153348802321105996DOI Listing
December 2002
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