Junepyo Oh

Bio: Junepyo Oh is an academic researcher from Applied Science Private University. The author has contributed to research in topics: Scanning tunneling microscope & Scattering. The author has an hindex of 14, co-authored 26 publications receiving 382 citations. Previous affiliations of Junepyo Oh include University of Tsukuba.

Self-organization of S adatoms on Au(111): √3R30° rows at low coverage.

Abstract: Using scanning tunneling microscopy, we observe an adlayer structure that is dominated by short rows of S atoms, on unreconstructed regions of a Au(111) surface. This structure forms upon adsorption of low S coverage (less than 0.1 monolayer) on a fully reconstructed clean surface at 300 K, then cooling to 5 K for observation. The rows adopt one of three orientations that are rotated by 30° from the close-packed directions of the Au(111) substrate, and adjacent S atoms in the rows are separated by √3 times the surface lattice constant, a. Monte Carlo simulations are performed on lattice-gas models, derived using a limited cluster expansion based on density functional theory energetics. Models which include long-range pairwise interactions (extending to 5a), plus selected trio interactions, successfully reproduce the linear rows of S atoms at reasonable temperatures.

Cu2S3 complex on Cu(111) as a candidate for mass transport enhancement

Abstract: Citation: Walen, H., Liu, D. J., Oh, J., Lim, H., Evans, J. W., Aikens, C. M., . . . Thiel, P. A. (2015). Cu2S3 complex on Cu(111) as a candidate for mass transport enhancement. Physical Review B, 91(4), 7. doi:10.1103/PhysRevB.91.045426

Significant Reduction in Adsorption Energy of CO on Platinum Clusters on Graphite

Abstract: We have studied desorption of CO on a Pt-deposited highly oriented pyrolytic graphite (HOPG) surface by temperature programmed desorption of CO (CO-TPD), scanning tunneling microscope (STM), and He atom scattering (HAS). A desorption peak of CO at a significantly lower temperature of ∼270 K with a heating rate of 0.5 K/s is observed for Pt clusters on a flat terrace of HOPG. STM results indicate that the height of Pt clusters on the terraces of the HOPG surface is monatomic. It is concluded that the significant reduction in CO adsorption energy is due to a modified electronic structure as a result of the interface interaction between Pt clusters and the HOPG surface.

Reconstruction of steps on the Cu(111) surface induced by sulfur

Abstract: A rich menagerie of structures is identified at 5 K following adsorption of low coverages (≤0.05 monolayers) of S on Cu(111) at room temperature. This paper emphasizes the reconstructions at the steps. The A-type close-packed step has 1 row of S atoms along its lower edge, where S atoms occupy alternating pseudo-fourfold-hollow (p4fh) sites. Additionally, there are 2 rows of S atoms of equal density on the upper edge, bridging a row of extra Cu atoms, together creating an extended chain. The B-type close-packed step exhibits an even more complex reconstruction, in which triangle-shaped groups of Cu atoms shift out of their original sites and form a base for S adsorption at (mostly) 4fh sites. We propose a mechanism by which these triangles could generate Cu–S complexes and short chains like those observed on the terraces.

Durability Investigation of Carbon Nanotube as Catalyst Support for Proton Exchange Membrane Fuel Cell Electrode

Abstract: Abstract Electrochemical surface oxidation of carbon black Vulcan XC-72 and multiwalled carbon nanotube (MWNT) has been compared following potentiostatic treatments up to 168 h under condition simulating PEMFC cathode environment (60 °C, N2 purged 0.5 M H2SO4, and a constant potential of 0.9 V). The subsequent electrochemical characterization at different treatment time intervals suggests that MWNT is electrochemically more stable than Vulcan XC-72 with less surface oxide formation and 30% lower corrosion current under the investigated condition. As a result of high corrosion resistance, MWNT shows lower loss of Pt surface area and oxygen reduction reaction activity when used as fuel cell catalyst support.

Active Sites and Mechanism of Oxygen Reduction Reaction Electrocatalysis on Nitrogen-Doped Carbon Materials.

Abstract: The oxygen reduction reaction (ORR) is a core reaction for electrochemical energy technologies such as fuel cells and metal-air batteries. ORR catalysts have been limited to platinum, which meets the requirements of high activity and durability. Over the last few decades, a variety of materials have been tested as non-Pt catalysts, from metal-organic complex molecules to metal-free catalysts. In particular, nitrogen-doped graphitic carbon materials, including N-doped graphene and N-doped carbon nanotubes, have been extensively studied. However, due to the lack of understanding of the reaction mechanism and conflicting knowledge of the catalytic active sites, carbon-based catalysts are still under the development stage of achieving a performance similar to Pt-based catalysts. In addition to the catalytic viewpoint, designing mass transport pathways is required for O2 . Recently, the importance of pyridinic N for the creation of active sites for ORR and the requirement of hydrophobicity near the active sites have been reported. Based on the increased knowledge in controlling ORR performances, bottom-up preparation of N-doped carbon catalysts, using N-containing conjugative molecules as the assemblies of the catalysts, is promising. Here, the recent understanding of the active sites and the mechanism of ORRs on N-doped carbon catalysts are reviewed.

Coupling Sub-Nanometric Copper Clusters with Quasi-Amorphous Cobalt Sulfide Yields Efficient and Robust Electrocatalysts for Water Splitting Reaction

Abstract: Superefficient water-splitting materials comprising sub-nanometric copper clusters and quasi-amorphous cobalt sulfide supported on copper foam are reported. While working together at both the anode and cathode sides of an alkaline electrolyzer, this material gives a catalytic output of overall water splitting comparable with the Pt/C-IrO2 -coupled electrolyzer.

Chemical structures of hydrazine-treated graphene oxide and generation of aromatic nitrogen doping

Abstract: Park et al. use 13C and 15N solid-state NMR and X-ray photoelectron spectroscopy to study the chemical structure of hydrazine-treated graphite oxide. Hydrazine treatment is shown to lead to the incorporation of aromatic N2 moieties at the graphene edges and restore graphitic networks on the basal planes.

A theoretical simulation on the catalytic oxidation of CO on Pt/graphene

Abstract: The catalytic oxidation of CO on Pt/X-graphene (X = “pri” for pristine- or “SV” for defective-graphene with a single vacancy) is investigated using the first-principles method based on density functional theory. In contrast to a Pt atom on pristine graphene, a vacancy defect in graphene strongly stabilizes a single Pt adatom and makes the Pt adatom more positively charged, which helps to weaken the CO adsorption and facilitates the O2 adsorption, thus enhancing the activity for CO oxidation and alleviating the CO poisoning of the platinum catalysts. The CO oxidation reaction on Pt/SV-graphene has a low energy barrier (0.58 eV) by the Langmuir–Hinshelwood (LH) reaction (CO + O2 → OOCO → CO2 + Oads) which is followed by the Eley–Rideal (ER) reaction with an energy barrier of 0.59 eV (CO + Oads → CO2). The results validate the reactivity of catalysts on the atomic-scale and initiate a clue for fabricating carbon-based catalysts with low cost and high activity.