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Chen T.-Y.,National Tsing Hua University | Chen T.-Y.,Institute of Nuclear Engineering and Science | Li H.D.,National Tsing Hua University | Lee G.-W.,National Tsing Hua University | And 7 more authors.
Physical Chemistry Chemical Physics | Year: 2015

Atomic-scale gold clusters were intercalated at the inter-facet corner sites of Pt-shell Ru-core nanocatalysts with near-monolayer shell thickness. We demonstrated that these unique clusters could serve as a drain of valence electrons in the kink region of the core-shell heterojunction. As jointly revealed by density functional theory calculations and valence band spectra, these Au clusters extract core-level electrons to the valence band. They prevent corrosion due to protonation and enhance the tolerance of CO by increasing the electronegativity at the outermost surface of the NCs during the methanol oxidation reaction (MOR). In these circumstances, the retained current density of Pt-shell Ru-core NCs is doubled in a long-term (2 hours) MOR at a fixed voltage (0.5 V vs. SCE) by intercalating these sub-nanometer gold clusters. Such novel structural confinement provides a possible strategy for developing direct-methanol fuel cell (DMFC) modules with high power and stability. © the Owner Societies.

Lan K.-C.,National Tsing Hua University | Hunag J.-H.,National Tsing Hua University | Ai C.-F.,Institute of Nuclear Energy Research of Taiwan | Yu G.-P.,National Tsing Hua University | Yu G.-P.,Institute of Nuclear Engineering and Science
Journal of Vacuum Science and Technology A: Vacuum, Surfaces and Films | Year: 2011

The main objective of this study was to investigate the structure and properties of ZrN xO y thin films associated with oxygen content and film thickness. ZrN xO y thin films were deposited using hollow cathode discharge ion plating on Si (100) substrate. The thickness of ZrN xO y films increased with increasing oxygen flow rate, ranging from 143 to 894 nm. Phase separation from ZrN xO y to ZrN and monoclinic ZrO 2 (m -ZrO 2) was observed by x-ray diffraction (XRD). The electrical and mechanical properties were influenced by the film thickness and the amount of separated phase, m -ZrO 2. ZrN xO y thin films with smaller thickness or deposited at higher O 2 flow rate were found to have higher electrical resistivity. Hardness of the ZrN xO y thin films increased with increasing thickness, which could be related to microstructure change of the thin films. Residual stress of the ZrN phase in the ZrN xO y thin films, measured using the modified sin 2 ψ XRD method, decreased with increasing oxygen flow rate. The thickness dependence of the residual stress in ZrN was different with different oxygen flow rates. The average residual stress of the ZrN xO y thin films also decreased with increasing oxygen flow rate and the stress did not showed significant dependence on the film thickness. © 2011 American Vacuum Society.

Yang P.-W.,National Tsing Hua University | Liu Y.-T.,National Chung Hsing University | Hsu S.-P.,National Central University | Wang K.-W.,National Central University | And 4 more authors.
CrystEngComm | Year: 2015

The growth of platinum shell crystals on the heterogeneous facets of ruthenium metal nanocrystals was investigated via in situ small angle X-ray scattering analysis. Our results illustrated that the pathway of shell crystal growth is mainly affected by controlling the incubation time prior to the thermal reduction of Pt ions by polyol radicals. For short incubation times, the shell crystal grows on the <111> radial facets and the <200> face facets of the nano-cylinder core via heterogeneous nucleation and crystal growth with and without assistance by transmetallation, respectively. On the other hand, severe chemical etching was observed prior to shell crystal growth after incubation for 2 hours. Consequently, the shell structure is formed from the nucleation of a PtRu alloy followed by the growth of Pt crystals. In both cases, dynamic restructuring at the core-shell interface was observed upon deposition of the shell crystal. These results enable the development of core-shell crystallites in expected configurations and with tuneable atomic structures. © 2015 The Royal Society of Chemistry.

Chen T.-Y.,National Tsing Hua University | Chen T.-Y.,Institute of Nuclear Engineering and Science | Lee G.-W.,National Tsing Hua University | Liu Y.-T.,Tunghai University | And 4 more authors.
Journal of Materials Chemistry A | Year: 2014

This research demonstrated that the methanol oxidation reaction triggers the protonation corrosion on the multi-walled carbon nanotube supported bimetallic nanocatalysts (NCs) in different geometrical configurations. Such corrosion pathways are confined by the geometrical configuration of the heterogeneous interfaces at the bimetallic oxide nanoparticles. In bimetallic alloyed NCs, the platinum (Pt) and ruthenium (Ru) domains were exposed simultaneously to the redox environment, therefore, the geometrical confinement on the atomic restructure is weak. This leads to substantial dissolution followed by the regrowth of hydrophilic components in redox conditions. For core-shell NCs, the shell crystal would prevent the core from direct contact with the redox environments. The heteroatomic junction forms ordered Pt atomic stacking at the ruthenium oxide crystallite. Such conformation confinement enhanced the Pt to Ru charge donation, thus the CO tolerance factor was also enhanced by more than two orders of magnitude when compared to the module durability of the direct methanol fuel cell compared to that of PtRu alloy. This journal is © The Royal Society of Chemistry.

Chang K.-H.,Institute of Nuclear Engineering and Science | Chen S.-M.,Institute of Nuclear Engineering and Science | Yeh T.-K.,Institute of Nuclear Engineering and Science | Kai J.-J.,Institute of Nuclear Engineering and Science
Corrosion Science | Year: 2014

The corrosive behavior of Alloy 625 in supercritical water at 700°C and 24.8MPa with dissolved oxygen contents of 150ppb, 1ppm, and 8.3ppm was studied. The oxides grown on all test samples exhibited a duplex-layer structure. The outer layer was composed of a spinel oxide Ni(Cr, Fe)2O4 and the inner layer was mainly continuous Cr2O3. Ni-containing oxides, such as spinel Ni(Cr, Fe)2O4, did not form on samples exposed to the supercritical water environment containing 150ppb dissolved oxygen. Oxygen content might considerably affect the composition and structure of oxides grown in supercritical water for Alloy 625. © 2013 Elsevier Ltd.

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