Dae Jong You

Ultrastable Pt nanoparticles supported on sulfur-containing ordered mesoporous carbonvia strong metal-support interaction

Sulfur-containing ordered mesoporous carbon (S-OMC) material was successfully obtained from a mesoporous silica template through a nano-replication method using p-toluenesulfonic acid as the framework source. The S-OMC material thus obtained could be utilized as an excellent support for Pt nanoparticles of size 3.14 nm, even though the Pt loading was 60 wt%. The Pt nanoparticles supported on the S-OMC material (Pt/S-OMC) exhibited excellent thermal stability compared with those supported on sulfur-free ordered mesoporous carbon and Vulcan carbon. XPS analysis indicated that the strong metal-support interaction between the sulfur atoms in the S-OMC support and the surface atoms of the loaded Pt nanoparticles played an important role in stabilization of the Pt nanoparticles against the Ostwald ripening process during the thermal treatments. Cyclic voltammogram results revealed that the Pt/S-OMC material exhibited reasonably high electrochemically active Pt surface areas before and after thermal treatments at 600 °C, indicating that the surface of Pt nanoparticles was not poisoned by the sulfur atoms of the S-OMC support.

Ordered mesoporous carbon–carbon nanotube nanocomposites as highly conductive and durable cathode catalyst supports for polymer electrolyte fuel cells

Ordered mesoporous carbon–carbon nanotube (OMC–CNT) nanocomposites were prepared and used as catalyst supports for polymer electrolyte fuel cells. The OMC–CNT composites were synthesized via a nanocasting method that used ordered mesoporous silica as a template and Ni–phthalocyanine as a carbon source. For comparison, sucrose and phthalocyanine were used to generate two other OMCs, OMC(Suc) and OMC(Pc), respectively. All three carbons exhibited hexagonally ordered mesostructures and uniform mesopores. Among the three carbons the OMC–CNT nanocomposites showed the highest electrical conductivity, which was due to the nature of their graphitic framework as well as their lower interfacial resistance. The three carbons were then used as fuel cell catalyst supports. It was found that highly dispersed Pt nanoparticles (ca. ∼1.5 nm in size) could be dispersed on the OMCs via a simple impregnation–reduction method. The activity and kinetics of the oxygen reduction reaction (ORR), measured by the rotating ring-disk electrode technique revealed that the ORR over the Pt/OMC catalysts followed a four-electron pathway. Among the three Pt/OMC catalysts, the Pt/OMC–CNT catalyst resulted in the highest ORR activity, and after an accelerated durability test the differences in the ORR activities of the three catalysts became more pronounced. In single cell tests, the Pt/OMC–CNT-based cathode showed a current density markedly greater than those of the other two cathodes after a high-voltage degradation test. These results were supported by the fact that the Pt/OMC–CNT-based cathode had the lowest resistance, which was probed by electrochemical impedance spectroscopy (EIS). The results of the single cell tests as well as those of the EIS-based measurements indicate that the rigidly interconnected structure of the OMC–CNT as well as their highly conductive frameworks are concomitantly responsible for the OMC–CNT nanocomposites exhibiting higher current density and durability than the other two carbons.

Communication: Enhanced oxygen reduction reaction and its underlying mechanism in Pd-Ir-Co trimetallic alloys

Based on a combined density functional theory and experimental study, we present that the electrochemical activity of Pd3Co alloy catalysts toward oxygen reduction reaction (ORR) can be enhanced by adding a small amount of Ir. While Ir tends to favorably exist in the subsurface layers, the underlying Ir atoms are found to cause a substantial modification in the surface electronic structure. As a consequence, we find that the activation barriers of O/OH hydrogenation reactions are noticeably lowered, which would be mainly responsible for the enhanced ORR activity. Furthermore, our study suggests that the presence of Ir in the near-surface region can suppress Co out-diffusion from the Pd3Co substrate, thereby improving the durability of Pd-Ir-Co catalysts. We also discuss the relative roles played by Ir and Co in enhancing the ORR activity relative to monometallic Pd catalysts.

Effect of acid catalysts on carbonization temperatures for ordered mesoporous carbon materials

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Direct sulfonation of ordered mesoporous carbon for catalyst support of direct methanol fuel cell

Ordered mesoporous carbon (OMC) prepared by nano-replication method was directly functionalized with sulfonic acid group by using the ammonium sulfate salts. PtRu nanoparticles below 3 nm was supported on the sulfonated-OMC support with 70 wt% loading, and the resulting catalysts exhibited promising catalytic activity for methanol oxidation reactions.

High Performance Membrane Electrode Assemblies by Optimization of Processes and Supported Catalysts

© 2012 Pak et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. High Performance Membrane Electrode Assemblies by Optimization of Processes and Supported Catalysts

Ordered mesoporous carbon as new support for direct methanol fuel cell: controlling of microporosity and graphitic character

As a new carbon support for the fuel cell, ordered mesoporous carbon (OMC) was prepared by the nano template method using ordered mesoporous silica. The structural properties of OMC such as microporosity and graphitic character were controlled by addition of nano silica powder during synthesis of OMC or the uses of different carbon precursors. The performance of direct methanol fuel cell in the single cell was affected significantly by the graphitic character of OMC support.