Gyubong Kim

Carbon Monoxide-Tolerant Platinum Nanoparticle Catalysts on Defect-Engineered Graphene

We studied catalytic performance, particularly tolerance against CO poisoning and particle migration, of Pt nanoparticles dispersed on graphene using ab initio calculations. It was shown that the binding of Pt nanoparticles to graphene and the molecular adsorption on Pt can be controlled by introducing defects on graphene. Pt d-band center is a key parameter that is tailored by such defect formation. It is observed that the binding energy difference between H(2) and CO is well correlated with the d-band center, whereas individual H(2) and CO binding energies are not. Relative occupation ratio of H(2) on Pt in a CO environment showed that Pt nanoparticles can tolerate CO more than does bulk Pt when the particles are deposited on nitrogen-doped graphene.

Effect of vacancy defects in graphene on metal anchoring and hydrogen adsorption

The dispersion of transition and alkaline-earth metals on defective graphenes is studied using first-principles calculations. The effect of vacancy defects on binding properties of metal atoms to the graphene and with hydrogen molecules is particularly investigated. It is shown that vacancy defects enhance efficiently the metal binding energy and thus its dispersion, particularly for alkaline-earth metals. Mg on vacancy defects shows a substantial increase in its binding energy and hydrogen uptake capacity. Among metals considered, Ca-vacancy complexes are found to exhibit the most favorable hydrogen adsorption characteristics in terms of the binding energy and the capacity.

EFFECTIVE METAL DISPERSION IN PYRIDINELIKE NITROGEN DOPED GRAPHENES FOR HYDROGEN STORAGE

We study the pyridinelike nitrogen-doped graphene (PNG) with dispersed transition metal (TM) atoms as a potential hydrogen storage medium using the pseudopotential density functional method. It is found that highly localized states near the Fermi level, which are derived from the nitrogen defects, contribute to strong TM bindings and favorable hydrogen adsorption in the PNG. The strong TM binding prevents the metal aggregation and improves the material stability. The hydrogen molecular binding energy in TM+PNG complex is shown to be optimistic for room temperature storage and release.

Stress evolution during the oxidation of silicon nanowires in the sub-10 nm diameter regime

Using a reactive molecular dynamics simulation, the oxidation of Si nanowires (Si-NWs) with diameters of 5, 10, and 20 nm was investigated. The compressive stress at the interface between the oxide and the Si core decreased with increasing curvature in the sub-10 nm regime of the diameter, in contrast to the theory of self-limiting oxidation where rigid mechanical constraint of the Si core was assumed. The Si core of the thinner Si-NW was deformed more with surface oxidation, resulting in a lower compressive stress at the interface. These results explain the experimental observation of full oxidation of very thin Si-NWs.

Spin-polarized energy-gap opening in asymmetric bilayer graphene nanoribbons

Electronic and magnetic properties of bilayer zigzag graphene nanoribbon (bZGNR) are studied using pseudopotential density functional method. The edge atoms in the top and bottom layers of bZGNR make a weak hybridization, which leads to electronic structures different from monolayer ZGNR. For asymmetric bZGNR, where the top and bottom layers have different widths, one edge is pinched by the interlayer bonding and the other sustains antiferromagnetic ordering. A small amount of charge transfer occurs from narrower to wider layer, producing spin-polarized electron and hole pockets. External electric field produces asymmetric energy-gap opening for each spin component, inducing half-metallicity in bZGNR.