Si/TiO x Core/Shell Nanowires with Branched Cathode Support Structures for Pt Catalysts in PEM Fuel Cells
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Si/TiOx Core/Shell Nanowires with Branched Cathode Support Structures for Pt Catalysts in PEM Fuel Cells Xiaoli He1, Richard Phillips1, Anurag Kawde1, Robin Hansen1, Jae Ho Lee1, Isaac Lund1, Eric Eisenbraun1 and Robert E. Geer1 1 College of Nanoscale Science and Engineering, University at Albany, State University of New York, 255 Fuller Road, Albany, NY 12203, U.S.A. ABSTRACT There are several significant challenges that must be overcome for PEM fuel cell commercialization such as electrode flooding, carbon corrosion, and significant cost due to the high loading of the platinum catalyst. Thus, a new structure is proposed for the cathode catalyst support consisting of Si/TiOx core/shell nanowires with branched structures, which has the potential to reduce electrode flooding, increase stability, and dramatically reduce the required Pt loading. In this study, Pt-coated Si/TiOx core/shell nanowires with and without branches are compared. The Pt surface area on supports with branch structures was calculated to be more than 4 times larger than on supports without branch structures, while keeping the Pt loading at only about 0.1 mg/cm2 (for the samples with branched structures). SEM, XRD, AES, and TEM were used to characterize the morphologies and structures of the as-prepared samples. Branched Si/TiOx core/shell nanowire structures may be a promising catalyst support to enable commercialization of highly cost-efficient PEM fuel cells and to promote an era of clean energy usage. INTRODUCTION Conventional cathode catalyst supports for proton exchange membrane fuel cells (PEMFCs) based on colloidal carbon black encounter several challenges including electrode flooding and carbon corrosion, causing degradation of durability and efficiency in PEMFCs [13]. Also, the cost associated with high platinum catalyst loading is a technical barrier that hampers PEMFCs from commercialization [4]. Therefore, alternative support materials that provide sufficient electrochemical stability, good electronic conductivity, and different structural geometry are proposed and reported in the literature [4-7]. For example, TiOx has been reported to be an outstanding catalyst support material due to its good conductivity, stability, corrosion resistance and strong bonding with Pt [7, 8]. For this study a new catalyst support structure consisting of branched Si/TiOx core/shell nanowires (NWs) has been developed in order to maximize the accessible surface area of Pt catalyst coatings, thereby increasing the number of active Pt catalyst sites and thus enhancing the electrochemical performance. We then compared the branched structure with plain Si/TiOx core/shell NWs. Also in our study, atomic layer deposition (ALD) for TiOx and Pt deposition is used to obtain a uniform coverage of TiOx and Pt layers on SiNWs and more importantly to precisely control the thickness of both layers so that Pt loading can be easily tuned to a desired value (0.1mg/cm2 in this case). The new Si/TiOx core/shell NWs with branched structures may enable a lower catalyst cost but
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