Publications by authors named "Byungchan Han"

26 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

Fluorine-Decorated Graphene Nanoribbons for an Anticorrosive Polymer Electrolyte Membrane Fuel Cell.

ACS Appl Mater Interfaces 2021 Jun 3;13(23):26936-26947. Epub 2021 Jun 3.

Fuel Cell Research and Demonstration Center, New and Renewable Energy Institute, Korea Institute of Energy Research (KIER), Buan-gun, Jeollabuk-do 56332, Republic of Korea.

Pt-supported carbon material-based electrocatalysts are formidably suffering from carbon corrosion when HO and O molecules are present at high voltages in polymer electrolyte membrane fuel cells (PEMFCs). In this study, we discovered that the edge site of a fluorine-doped graphene nanoribbon (F-GNR) was slightly adsorbed with HO and was thermodynamically unfavorable with O atoms after defining the thermodynamically stable structure of the F-GNR from DFT calculations. Based on computational predictions, the physicochemical and electrochemical properties of F-GNRs with/without Pt nanoparticles derived from a modified Hummer's method and the polyol process were investigated as support materials for electrocatalysts and additives in the cathode of a PEMFC, respectively. The Pt/F-GNR showed the lowest degradation rate in carbon corrosion and was effective in the cathode as additives, resulting from the enhanced carbon corrosion durability owing to the improved structural stability and water management. Notably, the F-GNR with highly stable carbon corrosion contributed to achieving a more durable PEMFC for long-term operation.
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http://dx.doi.org/10.1021/acsami.1c04132DOI Listing
June 2021

Optical bioelectronic nose of outstanding sensitivity and selectivity toward volatile organic compounds implemented with genetically engineered bacteriophage: Integrated study of multi-scale computational prediction and experimental validation.

Biosens Bioelectron 2021 Apr 13;177:112979. Epub 2021 Jan 13.

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

Genetic engineering of a bacteriophage is a promising way to develop a highly functional biosensor. Almost countless configurational degree of freedom in the manipulation, considerable uncertainty and cost involved with the approach, however, have been huddles for the objective. In this paper, we demonstrate rapidly responding optical biosensor with high selectivity toward gaseous explosives with genetically engineered phages. The sensors are equipped with peptide sequences in phages optimally interacting with the volatile organic compounds (VOCs) in visible light regime. To overcome the conventional issues, we use extensive utilization of empirical calculations to construct a large database of 8000 tripeptides and screen the best for electronic nose sensing performance toward nine VOCs belonging to three chemical classes. First-principles density functional theory (DFT) calculations unveil underlying correlations between the chemical affinity and optical property change on an electronic band structure level. The computational outcomes are validated by in vitro experimental design and testing of multiarray sensors using genetically modified phage implemented with five selected tripeptide sequences and wild-type phages. The classification success rates estimated from hierarchical cluster analysis are shown to be very consistent with the calculations. Our optical biosensor demonstrates a 1 ppb level of sensing resolution for explosive VOCs, which is a substantial improvement over conventional biosensor. The systematic interplay of big data-based computational prediction and in situ experimental validation can provide smart design principles for unconventionally outstanding biosensors.
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http://dx.doi.org/10.1016/j.bios.2021.112979DOI Listing
April 2021

Defect structure evolution of polyacrylonitrile and single wall carbon nanotube nanocomposites: a molecular dynamics simulation approach.

Sci Rep 2020 Jul 16;10(1):11816. Epub 2020 Jul 16.

Department of Organic Material Science and Engineering, Pusan National University, 2, Busandaehak-ro 63beon-gil, Geumjeong-gu, Busan, 46241, Republic of Korea.

In this study, molecular dynamics simulations were performed to understand the defect structure development of polyacrylonitrile-single wall carbon nanotube (PAN-SWNT) nanocomposites. Three different models (control PAN, PAN-SWNT(5,5), and PAN-SWNT(10,10)) with a SWNT concentration of 5 wt% for the nanocomposites were tested to study under large extensional deformation to the strain of 100% to study the corresponding mechanical properties. Upon deformation, the higher stress was observed in both nanocomposite systems as compared to the control PAN, indicating effective reinforcement. The higher Young's (4.76 ± 0.24 GPa) and bulk (4.19 ± 0.25 GPa) moduli were observed when the smaller-diameter SWNT was used, suggesting that SWNT resists stress better. The void structure formation was clearly observed in PAN-SWNT, while the nanocomposite with smaller diameter SWNT did not show the development of such a defect structure. In addition, the voids at the end of SWNT became larger in the drawing direction with increasing deformation.
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http://dx.doi.org/10.1038/s41598-020-68812-7DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7366919PMC
July 2020

Unique design of superior metal-organic framework for removal of toxic chemicals in humid environment via direct functionalization of the metal nodes.

J Hazard Mater 2020 11 18;398:122857. Epub 2020 May 18.

Research Center for Nanocatalysts, Korea Research Institute of Chemical Technology (KRICT), Jang-dong, Yuseong, Daejeon 34114, Republic of Korea; Department of Advanced Materials and Chemical Engineering, University of Science and Technology (UST), Gajeong-dong, Yuseong, Daejeon 34113, Republic of Korea. Electronic address:

Unique chemical and thermal stabilities of a zirconium-based metal-organic framework (MOF) and its functionalized analogues play a key role to efficiently remove chemical warfare agents (ex., cyanogen chloride, CNCl) and simulant (dimethyl methylphosphonate, DMMP) as well as industrial toxic gas, ammonia (NH). Herein, we for the first time demonstrate outstanding performance of MOF-808 for removal of toxic chemicals in humid environment via special design of functionalization of hydroxo species bridging Zr-nodes using a triethylenediamine (TEDA) to form ionic frameworks by gas phase acid-base reactions. In situ experimental analyses and first-principles density functional theory calculations unveil underlying mechanism on the selective deposition of TEDA on the Zr-bridging hydroxo sites (μ-OH) in Zr-MOFs. The crystal structure of TEDA-grafted MOF-808 was confirmed using synchrotron X-ray powder diffraction (SXRPD). Furthermore, operando FT-IR spectra elucidate why the TEDA-grafted MOF-808 shows by far superior sorption efficiency to other MOF varieties. This work provides design principles and applications how to optimize MOFs for the preparation for versatile adsorbents using diamine grafting chemistry, which is also potentially applicable to various catalysis.
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http://dx.doi.org/10.1016/j.jhazmat.2020.122857DOI Listing
November 2020

Critical differences in 3D atomic structure of individual ligand-protected nanocrystals in solution.

Science 2020 04;368(6486):60-67

Center for Nanoparticle Research, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea.

Precise three-dimensional (3D) atomic structure determination of individual nanocrystals is a prerequisite for understanding and predicting their physical properties. Nanocrystals from the same synthesis batch display what are often presumed to be small but possibly important differences in size, lattice distortions, and defects, which can only be understood by structural characterization with high spatial 3D resolution. We solved the structures of individual colloidal platinum nanocrystals by developing atomic-resolution 3D liquid-cell electron microscopy to reveal critical intrinsic heterogeneity of ligand-protected platinum nanocrystals in solution, including structural degeneracies, lattice parameter deviations, internal defects, and strain. These differences in structure lead to substantial contributions to free energies, consequential enough that they must be considered in any discussion of fundamental nanocrystal properties or applications.
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http://dx.doi.org/10.1126/science.aax3233DOI Listing
April 2020

Thermochemical study for remediation of highly concentrated acid spill: Computational modeling and experimental validation.

Chemosphere 2020 May 5;247:126098. Epub 2020 Feb 5.

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

The release of concentrated acid solutions by chemical accidents is disastrous to our environmental integrity. Alkaline agents applied to remedy the acid spill catastrophe may lead to secondary damages such as vaporization or spread out of the fumes unless substantial amount of neutralization heat is properly controlled. Using a rigorous thermodynamic formalism proposed by Pitzer to account short-range ion interactions and various subsidiary reactions, we develop a systematic computational model enabling quantitative prediction of reaction heat and the temperature change over neutralization of strongly concentrated acid solutions. We apply this model to four acid solutions (HCl, HNO, HSO, and HF) of each 3 M-equivalent concentration with two neutralizing agents of calcium hydroxide (Ca(OH)) and sodium bicarbonate (NaHCO). Predicted reaction heat and temperature are remarkably consistent with the outcomes measured by our own experiments, showing a linear correlation factor R greater than 0.98. We apply the model to extremely concentrated acid solutions as high as 50 wt% where an experimental approach is practically restricted. In contrast to the extremely exothermic Ca(OH) agent, NaHCO even lowers solution temperatures after neutralization reactions. Our model enables us to identify a promising neutralizer NaHCO for effectively controlling concentrated acid spills and may be useful for establishment of proper strategy for other chemical accidents.
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http://dx.doi.org/10.1016/j.chemosphere.2020.126098DOI Listing
May 2020

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

Carrier scattering in quasi-free standing graphene on hexagonal boron nitride.

Nanoscale 2017 Oct;9(41):15934-15944

Department of Mechanical Engineering, Yonsei University, Seoul 120-749, Republic of Korea.

Graphene, a two-dimensional material with a honeycomb lattice, has been promoted as a next generation material because of its ultrafast charge carriers and superior electrical properties. Hexagonal boron nitride (h-BN) is an insulator explored as an ideal substrate for graphene with lattice-matching. Using raido-frequency (RF) transmission measurement which provides specific characteristics of carrier scattering in a device, we profoundly investigated the electrical properties of quasi-free standing graphene on h-BN. RF devices with graphene supported and encapsulated with h-BN were fabricated to analyze the RF signal at low temperatures from 100 to 300 K. We demonstrated the carrier behavior in graphene with thermally excited carriers and acoustic photon scattering according to heat energy. Both h-BN supported and encapsulated graphene showed a significant enhancement in RF transmission, which is close to a gold interconnector. Our device with graphene on h-BN exhibited concealed nonlinear characteristics at a specific temperature of 180 K due to the internal effects of acoustic phonon scattering, while a usual device with graphene on SiO/Si provided a linear variation. To anticipate the potential for electronic applications, the electrical circuit properties such as impedance, resistance, and inductance were extracted from the results of RF measurement.
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http://dx.doi.org/10.1039/c7nr04571aDOI Listing
October 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

Self-assembled nitrogen-doped fullerenes and their catalysis for fuel cell and rechargeable metal-air battery applications.

Nanoscale 2017 Jun;9(22):7373-7379

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

In this study, we report self-assembled nitrogen-doped fullerenes (N-fullerene) as non-precious catalysts, which are active for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), and thus applicable for energy conversion and storage devices such as fuel cells and metal-air battery systems. We screen the best N-fullerene catalyst at the nitrogen doping level of 10 at%, not at the previously known doping level of 5 or 20 at% for graphene. We identify that the compressive surface strain induced by doped nitrogen plays a key role in the fine-tuning of catalytic activity.
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http://dx.doi.org/10.1039/c7nr00930eDOI Listing
June 2017

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

Increasing strength and conductivity of Cu alloy through abnormal plastic deformation of an intermetallic compound.

Sci Rep 2016 08 4;6:30907. Epub 2016 Aug 4.

School of Materials Science and Engineering, Pusan National University, Busan 609-735, Korea.

The precipitation strengthening of Cu alloys inevitably accompanies lowering of their electric conductivity and ductility. We produced bulk Cu alloys arrayed with nanofibers of stiff intermetallic compound through a precipitation mechanism using conventional casting and heat treatment processes. We then successfully elongated these arrays of nanofibers in the bulk Cu alloys to 400% of original length without breakage at room temperature using conventional rolling process. By inducing such an one-directional array of nanofibers of intermetallic compound from the uniform distribution of fine precipitates in the bulk Cu alloys, the trade-off between strength and conductivity and between strength and ductility could be significantly reduced. We observed a simultaneous increase in electrical conductivity by 1.3 times and also tensile strength by 1.3 times in this Cu alloy bulk compared to the conventional Cu alloys.
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http://dx.doi.org/10.1038/srep30907DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4973219PMC
August 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

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

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

Improved Corrosion Resistance and Mechanical Properties of CrN Hard Coatings with an Atomic Layer Deposited Al2O3 Interlayer.

ACS Appl Mater Interfaces 2015 Dec 23;7(48):26716-25. Epub 2015 Nov 23.

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

A new approach was adopted to improve the corrosion resistance of CrN hard coatings by inserting a Al2O3 layer through atomic layer deposition. The influence of the addition of a Al2O3 interlayer, its thickness, and the position of its insertion on the microstructure, surface roughness, corrosion behavior, and mechanical properties of the coatings was investigated. The results indicated that addition of a dense atomic layer deposited Al2O3 interlayer led to a significant decrease in the average grain size and surface roughness and to greatly improved corrosion resistance and corrosion durability of CrN coatings while maintaining their mechanical properties. Increasing the thickness of the Al2O3 interlayer and altering its insertion position so that it was near the surface of the coating also resulted in superior performance of the coating. The mechanism of this effect can be explained by the dense Al2O3 interlayer acting as a good sealing layer that inhibits charge transfer, diffusion of corrosive substances, and dislocation motion.
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http://dx.doi.org/10.1021/acsami.5b08696DOI Listing
December 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

Toward new fuel cell support materials: a theoretical and experimental study of nitrogen-doped graphene.

ChemSusChem 2014 Sep 10;7(9):2609-20. Epub 2014 Jul 10.

Department of Energy Systems Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST), Daegu, 711-873 (Republic of Korea), Fax: (+82) 53-785-6409.

Nano-scale Pt particles are often reported to be more electrochemically active and stable in a fuel cell if properly displaced on support materials; however, the factors that affect their activity and stability are not well understood. We applied first-principles calculations and experimental measurements to well-defined model systems of N-doped graphene supports (N-GNS) to reveal the fundamental mechanisms that control the catalytic properties and structural integrity of nano-scale Pt particles. DFT calculations predict thermodynamic and electrochemical interactions between N-GNS and Pt nanoparticles in the methanol oxidation reaction (MOR) and oxygen reduction reaction (ORR). Moreover, the dissolution potentials of the Pt nanoparticles supported on GNS and N-GNS catalysts are calculated under acidic conditions. Our results provide insight into the design of new support materials for enhanced catalytic efficiency and long-term stability.
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http://dx.doi.org/10.1002/cssc.201402258DOI Listing
September 2014

First principles computational study on the electrochemical stability of Pt-Co nanocatalysts.

Nanoscale 2013 Sep;5(18):8625-33

Department of Energy Systems Engineering, DGIST, Daegu 711-873, Republic of Korea.

Using density functional theory (DFT) calculations, we identify the thermodynamically stable configurations of Pt-Co alloy nanoparticles of varying Co compositions and particle sizes. Our results indicate that the most thermodynamically stable structure is a shell-by-shell configuration where the Pt atom only shell and the Co only shell alternately stack and the outermost shell consists of a Pt skin layer. DFT calculations show that the structure has substantially higher dissolution potential of the outermost Pt shell compared with pure Pt nanoparticles of approximately the same size. Furthermore, our DFT calculations also propose that the shell-by-shell structure shows much better oxygen reduction reaction (ORR) activity than conventional bulk or nanoparticles of pure Pt. These novel catalyst properties can be changed when the surfaces are adsorbed with oxygen atoms via selective segregation followed by the electrochemical dissolution of the alloyed Co atoms. However, these phenomena are thermodynamically not plausible if the chemical potentials of oxygen are controlled below a certain level. Therefore, we propose that the shell-by-shell structures are promising candidates for highly functional catalysts in fuel cell applications.
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http://dx.doi.org/10.1039/c3nr02611fDOI Listing
September 2013

Electrochemical stability of nanometer-scale Pt particles in acidic environments.

J Am Chem Soc 2010 Jan;132(2):596-600

Arizona State University, Tempe, Arizona 85287-8706, USA.

Understanding and controlling the electrochemical stability or corrosion behavior of nanometer-scale solids is vitally important in a variety of applications such as nanoscale electronics, sensing, and catalysis. For many applications, the increased surface to volume ratio achieved by particle size reduction leads to lower materials cost and higher efficiency, but there are questions as to whether the intrinsic stability of materials also decreases with particle size. An important example of this relates to the stability of Pt catalysts in, for example, proton exchange fuel cells. In this Article, we use electrochemical scanning tunneling microscopy to, for the first time, directly examine the stability of individual Pt nanoparticles as a function of applied potential. We combine this experimental study with ab initio computations to determine the stability, passivation, and dissolution behavior of Pt as a function of particle size and potential. Both approaches clearly show that smaller Pt particles dissolve well below the bulk dissolution potential and through a different mechanism. Pt dissolution from a nanoparticle occurs by direct electro-oxidation of Pt to soluble Pt(2+) cations, unlike bulk Pt, which dissolves from the oxide. These results have important implications for understanding the stability of Pt and Pt alloy catalysts in fuel cell architectures, and for the stability of nanoparticles in general.
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http://dx.doi.org/10.1021/ja9071496DOI Listing
January 2010
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