Formation of Micro and Nanostructured Nickel/Silica and Nickel/Metal Composites by Electrodeposition of Mesoporous Silic
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Formation of M icro and Nanostructured Nickel/Silica and Nickel/Metal Composites by E lectrodeposition of Mesoporous Silica onto Nickel Foam Nikolaus L. Cordes1 and Martin G. Bakker1,2 1 Department of Chemistry, The University of Alabama, Tuscaloosa, AL 35487-0336, U.S.A. 2 Center for Materials for Information Technology, The University of Alabama Tuscaloosa, AL 35487-0209, U.S.A. A BST R A C T Extremely high surface area porous electrodes are of interest as current collectors for advanced batteries and as the basis for supercapacitors. For moderate to large scale storage applications a three-dimensional material is needed with porosity at multiple length scales. We are developing a combined bottom up/top down approach to creating such materials by using electrodeposition of mesoporous silica on nickel foam, a commercially available porous conductor widely used as the current collector in various batteries. Electrodeposition produces a conformal coating on the nickel foam. By controlling the electrodeposition time the morphology of the mesoporous silica can be varied from a thin film up to 500 nm thick to a loosely bound agglomeration of mesoporous silica particles capable of completely filling the 0.3-0.5 mm voids of the nickel foam. The internal diameter of the mesopores in the silica can be controlled in the range 2.5-4.8 nm by changing the chain length of the templating surfactant used. Gas adsorption shows surface areas of 400-1600 m2/g of silica deposited, consistent with the assumed structure of the material. INTRODUC TION There are many uses for very high surface area porous metals including as current collectors in batteries and supercapacitors. Nickel foam1 is a widely used, cheap material, which has a relatively low surface area of only 5 m2/g. Given the commercial availability of this material, there is interest in ways of significantly increasing this surface area. Previous work2 has reported on the use of mesoporous silica dipcoated onto nickel foam as a template for the formation of nickel nanowire networks. More recently, ordered mesoporous silica has been deposited onto planar substrates using electrochemically assisted self assembly (EASA). 3,4 Electrochemical reduction of nitrates and hydrogen ions in the silica sol-gel mixture results in silica condensation due to the increase in the local pH. Our previous work has shown that electrochemically depositing silica using cetyltrimethylammonium bromide as a surfactant template onto nickel foam substrates leads to high surface area electrodes.5 We report here on the extension of this work to investigate the use of different surfactant chain lengths in the range C12 to C18. E X PE R I M E N T A L Mesoporous silica films on three dimensional electrodes were fabricated by EASA. The silica sol-gel solution consisted of 50 mL of aqueous 0.1 M NaNO3 + 0.01 M HCl, 50 mL of
ethanol, 7.54 mL of tetraethyl orthosilicate (TEOS), and either hexadecyltrimethylammonium bromide (CTAB; Sigma 99%, Acros Organics 99%), dodecyltrimethylammonium bromide (DTAB; TCI Amer
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