Publications by authors named "Joonhee Kang"

14 Publications

  • Page 1 of 1

First-Principles-Based Machine-Learning Molecular Dynamics for Crystalline Polymers with van der Waals Interactions.

J Phys Chem Lett 2021 Jul 24;12(25):6000-6006. Epub 2021 Jun 24.

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722, Republic of Korea.

Machine-learning (ML) techniques have drawn an ever-increasing focus as they enable high-throughput screening and multiscale prediction of material properties. Especially, ML force fields (FFs) of quantum mechanical accuracy are expected to play a central role for the purpose. The construction of ML-FFs for polymers is, however, still in its infancy due to the formidable configurational space of its composing atoms. Here, we demonstrate the effective development of ML-FFs using kernel functions and a Gaussian process for an organic polymer, polytetrafluoroethylene (PTFE), with a data set acquired by first-principles calculations and molecular dynamics (AIMD) simulations. Even though the training data set is sampled only with short PTFE chains, structures of longer chains optimized by our ML-FF show an excellent consistency with density functional theory calculations. Furthermore, when integrated with molecular dynamics simulations, the ML-FF successfully describes various physical properties of a PTFE bundle, such as a density, melting temperature, coefficient of thermal expansion, and Young's modulus.
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http://dx.doi.org/10.1021/acs.jpclett.1c01140DOI Listing
July 2021

First-principles database driven computational neural network approach to the discovery of active ternary nanocatalysts for oxygen reduction reaction.

Phys Chem Chem Phys 2018 Oct;20(38):24539-24544

Department of Chemical and Biomolecular Engineering, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722, Korea.

An elegant machine-learning-based algorithm was applied to study the thermo-electrochemical properties of ternary nanocatalysts for oxygen reduction reaction (ORR). High-dimensional neural network potentials (NNPs) for the interactions among the components were parameterized from big dataset established by first-principles density functional theory calculations. The NNPs were then incorporated with Monte Carlo (MC) and molecular dynamics (MD) simulations to identify not only active, but also electrochemically stable nanocatalysts for ORR in acidic solution. The effects of surface strain caused by selective segregation of certain components on the catalytic performance were accurately characterized. The computationally efficient and precise approach proposes a promising ORR candidate: 2.6 nm icosahedron comprising 60% of Pt and 40% Ni/Cu. Our methodology can be applied for high-throughput screening and designing of key functional nanomaterials to drastically enhance the performance of various electrochemical systems.
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http://dx.doi.org/10.1039/c8cp03801eDOI Listing
October 2018

First-principles study on thermodynamic stability of the hybrid interfacial structure of LiMnO cathode and carbonate electrolyte in Li-ion batteries.

Phys Chem Chem Phys 2018 May;20(17):11592-11597

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722, Republic of Korea.

The solid electrolyte interphase (SEI) of Li-ion batteries (LIBs) has been extensively studied, with most research focused on the anode, because of its significant impact on the prolonged cycle life, initial capacity loss, and safety issues. Using first-principles density functional theory (DFT) calculations and ab initio molecular dynamics (AIMD) simulations with the Hubbard correction, we examine the thermodynamic structure prediction and electrochemical stability of a spinel LiMn2O4 cathode interfaced with a carbonate electrolyte. The electronic energy levels of frontier orbitals of the electrolyte and the work function of the cathode offer clear characterization of the interfacial reactions. Our results based on both DFT calculations and AIMD simulations propose that the proton transfer mechanism at the hybrid interface is essential for initiating the SEI layer formation on the LiMn2O4 surface. Our results can be useful for identifying design concepts in the development of stable and high capacity LIBs with optimized electrodes and high-performance electrolytes.
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http://dx.doi.org/10.1039/c7cp08037aDOI Listing
May 2018

Effective Trapping of Lithium Polysulfides Using a Functionalized Carbon Nanotube-Coated Separator for Lithium-Sulfur Cells with Enhanced Cycling Stability.

ACS Appl Mater Interfaces 2017 Nov 24;9(44):38445-38454. Epub 2017 Oct 24.

Department of Chemical Engineering, Hanyang University , Seoul 04763, Korea.

The critical issues that hinder the practical applications of lithium-sulfur batteries, such as dissolution and migration of lithium polysulfides, poor electronic conductivity of sulfur and its discharge products, and low loading of sulfur, have been addressed by designing a functional separator modified using hydroxyl-functionalized carbon nanotubes (CNTOH). Density functional theory calculations and experimental results demonstrate that the hydroxyl groups in the CNTOH provoked strong interaction with lithium polysulfides and resulted in effective trapping of lithium polysulfides within the sulfur cathode side. The reduction in migration of lithium polysulfides to the lithium anode resulted in enhanced stability of the lithium electrode. The conductive nature of CNTOH also aided to efficiently reutilize the adsorbed reaction intermediates for subsequent cycling. As a result, the lithium-sulfur cell assembled with a functional separator exhibited a high initial discharge capacity of 1056 mAh g (corresponding to an areal capacity of 3.2 mAh cm) with a capacity fading rate of 0.11% per cycle over 400 cycles at 0.5 C rate.
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http://dx.doi.org/10.1021/acsami.7b10641DOI Listing
November 2017

First principles computational study on hydrolysis of hazardous chemicals phosphorus trichloride and oxychloride (PCl and POCl) catalyzed by molecular water clusters.

J Hazard Mater 2018 Jan 24;341:457-463. Epub 2017 Aug 24.

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 03722, Republic of Korea. Electronic address:

Using first principles calculations we unveil fundamental mechanism of hydrolysis reactions of two hazardous chemicals PCl and POCl with explicit molecular water clusters nearby. It is found that the water molecules play a key role as a catalyst significantly lowing activation barrier of the hydrolysis via transferring its protons to reaction intermediates. Interestingly, torsional angle of the molecular complex at transition state is identified as a vital descriptor on the reaction rate. Analysis of charge distribution over the complex further reinforces the finding with atomic level correlation between the torsional angle and variation of the orbital hybridization state of phosphorus (P) in the complex. Electronic charge separation (or polarization) enhances thermodynamic stability of the activated complex and reduces the activation energy through hydrogen bonding network with water molecules nearby. Calculated potential energy surfaces (PES) for the hydrolysis of PCl and POCl depict their two contrastingly different profiles of double- and triple-depth wells, respectively. It is ascribed to the unique double-bonding O=P in the POCl. Our results on the activation free energy show well agreements with previous experimental data within 7kcalmol deviation.
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http://dx.doi.org/10.1016/j.jhazmat.2017.08.054DOI Listing
January 2018

First principles computational study on the adsorption mechanism of organic methyl iodide gas on triethylenediamine impregnated activated carbon.

Phys Chem Chem Phys 2016 Nov;18(47):32050-32056

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, 03722, Republic of Korea.

We study removal of gas-phase organic methyl iodide (CHI) from an ambient environment via adsorption onto triethylenediamine (TEDA) impregnated activated carbon (AC). First principles density functional theory (DFT) calculations and ab-initio molecular dynamics (AIMD) simulations were extensively utilized to understand the underlying mechanism for the chemical reaction of CHI on the surface. Our results suggest that the adsorption energy of CHI shows substantial heterogeneity depending on the adsorption site, porosity of the AC, and humidity. It is observed that the CHI dissociative chemisorption is largely influenced by the adsorption site and porosity. Most importantly, it is clearly shown through free energy diagrams that the impregnated TEDA not only reduces the dissociation activation barrier of CHI but also attracts HO molecules relieving the AC surface from poisoning by humidity, and also enhances the removal efficiency of CHI through the chemical dissociation reaction. Our computational study can help to open new routes to design highly efficient materials for removing environmentally and biologically hazardous materials, for example radioactive iodine gas emitted following accidents at a nuclear power plant.
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http://dx.doi.org/10.1039/c6cp06483cDOI Listing
November 2016

First-Principles Design of Graphene-Based Active Catalysts for Oxygen Reduction and Evolution Reactions in the Aprotic Li-O2 Battery.

J Phys Chem Lett 2016 Jul 12;7(14):2803-8. Epub 2016 Jul 12.

Department of Chemical and Biomolecular Engineering, Yonsei University , Seoul 03722, Republic of Korea.

Using first-principles density functional theory (DFT) calculations, we demonstrate that catalytic activities toward oxygen reduction and evolution reactions (ORR and OER) in a Li-O2 battery can be substantially improved with graphene-based materials. We accomplish the goal by calculating free energy diagrams for the redox reactions of oxygen to identify a rate-determining step controlling the overpotentials. We unveil that the catalytic performance is well described by the adsorption energies of the intermediates LiO2 and Li2O2 and propose that graphene-based materials can be substantially optimized through either by N doping or encapsulating Cu(111) single crystals. Furthermore, our systematic approach with DFT calculations applied to design of optimum catalysts enables screening of promising candidates for the oxygen electrochemistry leading to considerable improvement of efficiency of a range of renewable energy devices.
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http://dx.doi.org/10.1021/acs.jpclett.6b01071DOI Listing
July 2016

First-Principles Characterization of the Unknown Crystal Structure and Ionic Conductivity of Li7P2S8I as a Solid Electrolyte for High-Voltage Li Ion Batteries.

J Phys Chem Lett 2016 Jul 30;7(14):2671-5. Epub 2016 Jun 30.

Department of Chemical and Biomolecular Engineering, Yonsei University , Seoul 03722, Republic of Korea.

Using first-principles density functional theory calculations and ab initio molecular dynamics (AIMD) simulations, we demonstrate the crystal structure of the Li7P2S8I (LPSI) and Li ionic conductivity at room temperature with its atomic-level mechanism. By successively applying three rigorous conceptual approaches, we identify that the LPSI has a similar symmetry class as Li10GeP2S12 (LGPS) material and estimate the Li ionic conductivity to be 0.3 mS cm(-1) with an activation energy of 0.20 eV, similar to the experimental value of 0.63 mS cm(-1). Iodine ions provide an additional path for Li ion diffusion, but a strong Li-I attractive interaction degrades the Li ionic transport. Calculated density of states (DOS) for LPSI indicate that electrochemical instability can be substantially improved by incorporating iodine at the Li metallic anode via forming a LiI compound. Our methods propose the computational design concept for a sulfide-based solid electrolyte with heteroatom doping for high-voltage Li ion batteries.
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http://dx.doi.org/10.1021/acs.jpclett.6b01050DOI Listing
July 2016

Oxygen-Deficient Zirconia (ZrO2-x): A New Material for Solar Light Absorption.

Sci Rep 2016 06 6;6:27218. Epub 2016 Jun 6.

Department of Energy Systems Engineering, DGIST, Daegu, 42988, Republic of Korea.

Here, we present oxygen-deficient black ZrO2-x as a new material for sunlight absorption with a low band gap around ~1.5 eV, via a controlled magnesiothermic reduction in 5% H2/Ar from white ZrO2, a wide bandgap(~5 eV) semiconductor, usually not considered for solar light absorption. It shows for the first time a dramatic increase in solar light absorbance and significant activity for solar light-induced H2 production from methanol-water with excellent stability up to 30 days while white ZrO2 fails. Generation of large amounts of oxygen vacancies or surface defects clearly visualized by the HR-TEM and HR-SEM images is the main reason for the drastic alteration of the optical properties through the formation of new energy states near valence band and conduction band towards Fermi level in black ZrO2-x as indicated by XPS and DFT calculations of black ZrO2-x. Current reduction method using Mg and H2 is mild, but highly efficient to produce solar light-assisted photocatalytically active black ZrO2-x.
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http://dx.doi.org/10.1038/srep27218DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4893729PMC
June 2016

Design of exceptionally strong and conductive Cu alloys beyond the conventional speculation via the interfacial energy-controlled dispersion of γ-Al2O3 nanoparticles.

Sci Rep 2015 Nov 30;5:17364. Epub 2015 Nov 30.

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, 03722, Korea.

The development of Cu-based alloys with high-mechanical properties (strength, ductility) and electrical conductivity plays a key role over a wide range of industrial applications. Successful design of the materials, however, has been rare due to the improvement of mutually exclusive properties as conventionally speculated. In this paper, we demonstrate that these contradictory material properties can be improved simultaneously if the interfacial energies of heterogeneous interfaces are carefully controlled. We uniformly disperse γ-Al2O3 nanoparticles over Cu matrix, and then we controlled atomic level morphology of the interface γ-Al2O3//Cu by adding Ti solutes. It is shown that the Ti dramatically drives the interfacial phase transformation from very irregular to homogeneous spherical morphologies resulting in substantial enhancement of the mechanical property of Cu matrix. Furthermore, the Ti removes impurities (O and Al) in the Cu matrix by forming oxides leading to recovery of the electrical conductivity of pure Cu. We validate experimental results using TEM and EDX combined with first-principles density functional theory (DFT) calculations, which all consistently poise that our materials are suitable for industrial applications.
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http://dx.doi.org/10.1038/srep17364DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4663622PMC
November 2015

Reliable and cost effective design of intermetallic Ni2Si nanowires and direct characterization of its mechanical properties.

Sci Rep 2015 Oct 12;5:15050. Epub 2015 Oct 12.

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul, 120-749, Republic of Korea.

We report that a single crystal Ni2Si nanowire (NW) of intermetallic compound can be reliably designed using simple three-step processes: casting a ternary Cu-Ni-Si alloy, nucleate and growth of Ni2Si NWs as embedded in the alloy matrix via designing discontinuous precipitation (DP) of Ni2Si nanoparticles and thermal aging, and finally chemical etching to decouple the Ni2Si NWs from the alloy matrix. By direct application of uniaxial tensile tests to the Ni2Si NW we characterize its mechanical properties, which were rarely reported in previous literatures. Using integrated studies of first principles density functional theory (DFT) calculations, high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDX) we accurately validate the experimental measurements. Our results indicate that our simple three-step method enables to design brittle Ni2Si NW with high tensile strength of 3.0 GPa and elastic modulus of 60.6 GPa. We propose that the systematic methodology pursued in this paper significantly contributes to opening innovative processes to design various kinds of low dimensional nanomaterials leading to advancement of frontiers in nanotechnology and related industry sectors.
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http://dx.doi.org/10.1038/srep15050DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4601013PMC
October 2015

First-Principles Study on the Thermal Stability of LiNiO2 Materials Coated by Amorphous Al2O3 with Atomic Layer Thickness.

ACS Appl Mater Interfaces 2015 Jun 22;7(21):11599-603. Epub 2015 May 22.

‡Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul 120-749, Republic of Korea.

Using first-principles calculations, we study how to enhance thermal stability of high Ni compositional cathodes in Li-ion battery application. Using the archetype material LiNiO2 (LNO), we identify that ultrathin coating of Al2O3 (0001) on LNO(012) surface, which is the Li de-/intercalation channel, substantially improves the instability problem. Density functional theory calculations indicate that the Al2O3 deposits show phase transition from the corundum-type crystalline (c-Al2O3) to amorphous (a-Al2O3) structures as the number of coating layers reaches three. Ab initio molecular dynamic simulations on the LNO(012) surface coated by a-Al2O3 (about 0.88 nm) with three atomic layers oxygen gas evolution is strongly suppressed at T=400 K. We find that the underlying mechanism is the strong contacting force at the interface between LNO(012) and Al2O3 deposits, which, in turn, originated from highly ionic chemical bonding of Al and O at the interface. Furthermore, we identify that thermodynamic stability of the a-Al2O3 is even more enhanced with Li in the layer, implying that the protection for the LNO(012) surface by the coating layer is meaningful over the charging process. Our approach contributes to the design of innovative cathode materials with not only high-energy capacity but also long-term thermal and electrochemical stability applicable for a variety of electrochemical energy devices including Li-ion batteries.
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http://dx.doi.org/10.1021/acsami.5b02572DOI Listing
June 2015

Gas sensing studies of pulsed laser deposition deposited WO3 nanorod based thin films.

J Nanosci Nanotechnol 2013 Dec;13(12):8315-9

School of Electrical and Computer Engineering, RMIT University City Campus, GPO Box 2476V, Melbourne, Australia.

WO3 nanorod based thin films were deposited via pulsed laser deposition onto quartz conductometric transducers with pre-patterned gold interdigitated transducers (IDT) employing the shortest wavelength (193 nm) ArF excimer laser. Micro-characterization techniques such as scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to study surface morphology and crystal structure. It was observed that the fabricated films showed nanocolumnar features perpendicular to the surface. The measured sizes of the nanorods were found to be approximately -50 nm in diameter. The high resolution TEM (HRTEM) image of the nanorods based WO3 showed the WO3 lattice spacing of 3.79 angstroms corresponding to the (020) plane of monoclinic WO3. Gas sensing characterizations of the developed sensors were tested towards hydrogen and ethanol at temperatures between room and 400 degrees C. The sensor exhibited high response towards H2 and ethanol at operating temperatures of 170 and 400 degrees C, respectively. The excellent sensing characteristics of WO3 films towards ethanol and H2 at low concentrations offer great potential for low cost and stable gas sensing.
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http://dx.doi.org/10.1166/jnn.2013.8210DOI Listing
December 2013

Portable RF-Sensor System for the Monitoring of Air Pollution and Water Contamination.

J Anal Methods Chem 2012 15;2012:568974. Epub 2012 Aug 15.

Department of Physics, University of Incheon, Incheon 402-749, Republic of Korea.

Monitoring air pollution including the contents of VOC, O(3), NO(2), and dusts has attracted a lot of interest in addition to the monitoring of water contamination because it affects directly to the quality of living conditions. Most of the current air pollution monitoring stations use the expensive and bulky instruments and are only installed in the very limited area. To bring the information of the air and water quality to the public in real time, it is important to construct portable monitoring systems and distribute them close to our everyday living places. In this work, we have constructed a low-cost portable RF sensor system by using 400 MHz transceiver to achieve this goal. Accuracy of the measurement was comparable to the ones used in the expensive and bulky commercial air pollution forecast systems.
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http://dx.doi.org/10.1155/2012/568974DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3426251PMC
August 2012
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