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Malek K.,NRC Institute for Fuel Cell Innovation | Sahimi M.,University of Southern California
Journal of Chemical Physics | Year: 2010

Silicon carbide nanotubes (SiCNTs) are new materials with excellent properties, such as high thermal stability and mechanical strength, which are much improved over those of their carboneous counterparts, namely, carbon nanotubes (CNTs). Gas separation processes at high temperatures and pressures may be improved by developing mixed-matrix membranes that contain SiCNTs. Such nanotubes are also of interest in other important processes, such as hydrogen production and its storage, as well as separation by supercritical adsorption. The structural parameters of the nanotubes, i.e., their diameter, curvature, and chirality, as well as the interaction strength between the gases and the nanotubes' walls, play a fundamental role in efficient use of the SiCNTs in such processes. We employ molecular dynamics simulations in order to examine the adsorption and diffusion of N2, H2, CO2, CH4, and n C4H10 in the SiCNTs, as a function of the pressure and the type of the nanotubes, namely, the zigzag, armchair, and chiral tubes. The simulations indicate the strong effect of the nanotubes' chirality and curvature on the pressure dependence of the adsorption isotherms and the self-diffusivities. Detailed comparison is made between the results and those for the CNTs. In particular, we find that the adsorption capacity of the SiCNTs for hydrogen is higher than the CNTs' under the conditions that we have studied. © 2010 American Institute of Physics.

Malek K.,NRC Institute for Fuel Cell Innovation | Malek K.,Simon Fraser University | Franco A.A.,CEA Grenoble
Journal of Physical Chemistry B | Year: 2011

This work is comprised of a versatile multiscale modeling of carbon corrosion processes in catalyst layers (CLs) of polymer electrolyte fuel cells (PEFCs). Slow rates of electrocatalytic processes in CLs and materials aging are the main sources of voltage loss in PEFCs under realistic operating conditions. We combined microstructure data obtained from coarse-grained molecular dynamics (CGMD) simulations with a detailed description of the nanoscale elementary kinetic processes and electrochemical double-layer effects at the catalyst/electrolyte and carbon/electrolyte interfaces. We exclusively focused on morphology and microstructure changes in the catalyst layer of PEFCs as a result of carbon corrosion. By employing extensive CGMD simulations, we analyzed the microstructure of CLs as a function of carbon loss and in view of ionomer and water morphology, water and ionomer coverage, and overall changes in carbon surface. These ingredients are integrated into a kinetic model, which allows capture of the impact of the structural changes on the PEFC performance decay. In principle, such multiscale simulation studies allow a relation of the aging of CLs to the selection of carbon particles (sizes and wettability), the catalyst loading, and the level of ionomer structural changes during the CL degradation process. © Published 2011 by the American Chemical Society.

Chen H.M.,National Taiwan University | Chen C.K.,National Taiwan University | Liu R.-S.,National Taiwan University | Zhang L.,NRC Institute for Fuel Cell Innovation | And 2 more authors.
Chemical Society Reviews | Year: 2012

This review concerns the efficient conversion of sunlight into chemical fuels through the photoelectrochemical splitting of water, which has the potential to generate sustainable hydrogen fuel. In this review, we discuss various photoelectrode materials and relative design strategies with their associated fabrication for solar water splitting. Factors affecting photoelectrochemical performance of these materials and designs are also described. The most recent progress in the research and development of new materials as well as their corresponding photoelectrodes is also summarized in this review. Finally, the research strategies and future directions for water splitting are discussed with recommendations to facilitate the further exploration of new photoelectrode materials and their associated technologies. © The Royal Society of Chemistry 2012.

Wang G.,University of South China | Wang G.,NRC Institute for Fuel Cell Innovation | Zhang L.,NRC Institute for Fuel Cell Innovation | Zhang J.,NRC Institute for Fuel Cell Innovation
Chemical Society Reviews | Year: 2012

In this critical review, metal oxides-based materials for electrochemical supercapacitor (ES) electrodes are reviewed in detail together with a brief review of carbon materials and conducting polymers. Their advantages, disadvantages, and performance in ES electrodes are discussed through extensive analysis of the literature, and new trends in material development are also reviewed. Two important future research directions are indicated and summarized, based on results published in the literature: the development of composite and nanostructured ES materials to overcome the major challenge posed by the low energy density of ES (476 references). © 2012 The Royal Society of Chemistry.

Wang Y.-J.,University of British Columbia | Wang Y.-J.,NRC Institute for Fuel Cell Innovation | Wilkinson D.P.,University of British Columbia | Wilkinson D.P.,NRC Institute for Fuel Cell Innovation | Zhang J.,NRC Institute for Fuel Cell Innovation
Chemical Reviews | Year: 2011

The developments in the field of several important kinds of noncarbon supporting materials in recent years are reviewed. The challenges for developing noncarbon supporting materials are analyzed, and the possible future research directions, in particular the material preparation methods, are also proposed. To address the issue of carbon oxidation, effort has been placed on developing alternative noncarbon materials for catalyst supports. As compared to carbon-based supports, some noncarbon materials and their supported Pt-based catalysts have shown unique structures, suitable physical and chemical properties, and high catalytic activity toward fuel cell reactions such as the oxygen reduction reaction and small alcohol electrooxidation. To make noncarbon-supported Pt-based catalysts practically feasible in PEM fuel cells, material improvements in electronic conductivity, solubility, chemical/electrochemical and thermal stability, and surface area are required.

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