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861.
Hee-Tak Kim Dae Jong You Hae-Kwon Yoon Sang Hoon Joo Chanho Pak Hyuk Chang In-Seob Song 《Journal of power sources》2008,180(2):724-732
The development of a cathode catalyst layer based on a supported Pt catalyst using an ordered mesoporous carbon (OMC) for direct methanol fuel cell is reported. An OMC with a mesopore structure between hexagonally arranged carbon nanorods is prepared using a template method. Platinum nanoparticles are supported on the OMC (Pt/OMC) with high metal loading of 60 wt.%. Compositional and morphological variations are made by varying the ionomer content and by compressing the catalyst layer to detect a parameter that determines the power performance. Increase in power density with decrease in the volume fraction of ionomer in the agglomerate comprising the Pt/OMC and the ionomer indicates that mass transport through the ionomer phase governs the kinetics of oxygen reduction. Impedance spectroscopic analysis suggests that a significant mass-transport limitation occurs at high ionomer content and in the compressed cathode. The power density of the optimum cathode layer, which employs a Pt/OMC catalyst with a Pt loading of 2 mg cm−2, is greater than that of a catalyst layer with 6 mg cm−2 Pt-black catalyst at a voltage higher than 0.4 V. This would lead to a significant reduction in the cost of the membrane electrode assembly. 相似文献
862.
MP Golombek RA Cook T Economou WM Folkner AF Haldemann PH Kallemeyn JM Knudsen RM Manning HJ Moore TJ Parker R Rieder JT Schofield PH Smith RM Vaughan 《Canadian Metallurgical Quarterly》1997,278(5344):1743-1748
Chemical analyses returned by Mars Pathfinder indicate that some rocks may be high in silica, implying differentiated parent materials. Rounded pebbles and cobbles and a possible conglomerate suggest fluvial processes that imply liquid water in equilibrium with the atmosphere and thus a warmer and wetter past. The moment of inertia indicates a central metallic core of 1300 to 2000 kilometers in radius. Composite airborne dust particles appear magnetized by freeze-dried maghemite stain or cement that may have been leached from crustal materials by an active hydrologic cycle. Remote-sensing data at a scale of generally greater than approximately 1 kilometer and an Earth analog correctly predicted a rocky plain safe for landing and roving with a variety of rocks deposited by catastrophic floods that are relatively dust-free. 相似文献
863.
Jun Hwan Park Kyung-Tae Park Yong Shin Lee Won Jong Nam 《Metallurgical and Materials Transactions A》2005,36(5):1365-1368
The compression behaviors of well-annealed coarsegrained (CG) and ultrafine-grained (UFG) 5083 Al alloys at 77 and 298 K were
compared. For the CG alloy, stage II and III strain hardening were dominant at 77 and 298 K, respectively, depending on the
completeness of dislocation cell formation. The UFG alloy exhibited the elastic-near perfectly plastic behavior without distinctive
dislocation cell formation at both temperatures. For both alloys, the flow stress at 77 K was much higher than that at 298
K.
This work was supported by the Basic Research Program (Grant No. R01-2003-000-10202-0) of the Korea Science & Engineering
Foundation. 相似文献
864.
865.
FS Baker RA Daley RH Bradley 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2005,80(8):878-883
The surface oxygen content of selected wood‐based phosphoric acid‐activated carbons was quantified using X‐ray photoelectron spectroscopy (XPS) and correlated with the residual bulk phosphate levels of the carbons and their adsorptivity in solution. The adsorption of Al3+, Cu2+, and para‐chlorophenol, respectively, from water decreased as a function of increasing surface oxygen content of the carbons. When the carbon of lowest surface oxygen content was oxidized with ozone to impart a surface oxygen content comparable to that of a carbon with a much higher phosphate level, adsorption of Al3+, Cu2+, and para‐chlorophenol from water decreased proportionally. The increase in polarity of the carbon surface was accompanied by a decrease in pH and appeared to be the dominant factor with respect to the adsorption of the target species from water. Copyright © 2005 Society of Chemical Industry 相似文献
866.
Kyung Song Christoph T. Koch Ja Kyung Lee Dong Yeong Kim Jong Kyu Kim Amin Parvizi Woo Young Jung Chan Gyung Park Hyeok Jae Jeong Hyoung Seop Kim Ye Cao Tiannan Yang Long‐Qing Chen Sang Ho Oh 《Advanced Materials Interfaces》2015,2(1)
A key to strain engineering of piezoelectric semiconductor devices is the quantitative assessment of the strain‐charge relationship. This is particularly demanding in current InGaN/GaN‐based light‐emitting diode (LED) designs as piezoelectric effects are known to degrade the device performance. Using the state‐of‐the‐art inline electron holography, we have obtained fully quantitative maps of the two‐dimensional strain tensor and total charge density in conventional blue LEDs and correlated these with sub‐nanometer spatial resolution. We show that the In0.15Ga0.85N quantum wells are compressively strained and elongated along the polar growth direction, exerting compressive stress/strain on the GaN quantum barriers. Interface sheet charges arising from a polarization gradient are obtained directly from the strain data and compared with the total charge density map, quantitatively verifying only 60% of the polarization charges are screened by electrons, leaving a substantial piezoelectric field in each In0.15Ga0.85N quantum well. The demonstrated capability of inline electron holography provides a technical breakthrough for future strain engineering of piezoelectric optoelectronic devices. 相似文献
867.
Jun Mok Ha Sung Ho Yoo Jong Hoi Cho Yong Hoon Cho Sung Oh Cho 《Nanoscale research letters》2014,9(1):1-7
Silicon (Si) nanostructures that exhibit a significantly low reflectance in ultraviolet (UV) and visible light wavelength regions are fabricated using a hydrogen etching process. The fabricated Si nanostructures have aperiodic subwavelength structures with pyramid-like morphologies. The detailed morphologies of the nanostructures can be controlled by changing the etching condition. The nanostructured Si exhibited much more reduced reflectance than a flat Si surface: an average reflectance of the nanostructured Si was approximately 6.8% in visible light region and a slight high reflectance of approximately 17% in UV region. The reflectance was further reduced in both UV and visible light region through the deposition of a poly(dimethylsiloxane) layer with a rough surface on the Si nanostructure: the reflectance can be decreased down to 2.5%. The enhancement of the antireflection properties was analyzed with a finite difference time domain simulation method. 相似文献
868.
Thanh Binh Mai Thi Nga Tran Md. Rafiqul Islam Jong Myung Park Kwon Taek Lim 《Journal of Materials Science》2014,49(4):1519-1526
A facile method has been developed for the synthesis of core–shell nanostructure poly(N-isopropylacrylamide) grafted on silica nanoparticles (SiO2 NPs) by using the combination of ARGET ATRP and thiol-ene click chemistry. The covalent attachment of the thermo-responsive polymer was achieved by taking advantage of the fast, robust, and high efficient thiol-ene click reaction as demonstrated by FT-IR and XPS. The ARGET ATRP provides the good conversion of the monomer in a well-controlled manner as indicated by the narrow value of PDI (1.21). The grafting amount of the polymer on SiO2 NPs was found to be ca. 18 % as determined by TGA technique. TEM images of the encapsulated SiO2 NPs suggested that the SiO2 NPs core was covered by the soft polymer layer. Interestingly, dynamic light scattering analysis revealed that the as-synthesized nanocomposites exhibited the thermo-responsive behavior with the transition temperature around 31–33 °C. 相似文献
869.
870.
Hotspots: Hotspot‐Engineered 3D Multipetal Flower Assemblies for Surface‐Enhanced Raman Spectroscopy (Adv. Mater. 34/2014)
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