Direct solution-based reduction synthesis of Au, Pd, and Pt aerogels
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Lauren A. Morris Armament Research, Development and Engineering Center, U.S. Army RDECOM-ARDEC, Picatinny Arsenal, New Jersey 07806, USA
Joshua P. McClure United States Army Research Laboratory-Sensors and Electron Devices Directorate, Adelphi, Maryland 20783, USA
Madeline Y. Ryu and Jesse L. Palmer Department of Chemistry and Life Science, United States Military Academy, West Point, New York 10996, USA (Received 27 July 2017; accepted 25 September 2017)
Gold, palladium, and platinum aerogels were prepared by a rapid, direct solution-based reduction synthesis with densities of 0.54, 0.065, and 0.055 g/cm3, respectively. Salt solutions were reduced at 1:1 (v/v) with dimethylamine borane and sodium borohydride to rapidly form gels within seconds to minutes above a threshold salt concentration and were then rinsed and freeze dried. Au, Pd, and Pt aerogels had no presence of oxide phases confirmed by X-ray diffractometry. Specific surface areas determined with gas physisorption were 3.06, 15.43, and 20.56 m2/g for Au, Pd, and Pt. Electrochemically determined specific capacitances using electrochemical impedance spectroscopy and cyclic voltammetry were 2.18, 4.13, and 4.20 F/g, and 2.67, 7.99, and 5.12 F/g for Au, Pd, and Pt, respectively. The rapid synthesis, high solvent accessible specific surface area, conductivity, and capacitance make these noble metal aerogels candidates for many of catalytic, energy, and sensor applications. I. INTRODUCTION
Three-dimensional nanostructures possess desirable properties for a wide range of applications requiring control over chemical reactivity and mass transport properties.1 High specific surface area, porosity, and conductivity are beneficial for catalysis, energy storage and conversion, piezoelectrics, and sensors.2–5 Metallic 3-dimensional nanostructures further enhance high conductivity, ductility, malleability, and strength.6,7 Device integration ultimately requires that nanomaterials be freestanding or combined with support materials. An optimized support for many applications would offer a porous, conductive, and inert framework coated with an active material to a minimal thickness. Nanoparticle incorporation with support materials such as carbon is advantageous for minimizing the cost of active materials but often results in weak adsorption to the support and eventual agglomeration during device performance.8,9 Free-standing 3-dimensional metal nanomaterials offer a route to avoid this challenge. Metal and metal oxide 3-dimensional structures have been synthesized by
Contributing Editor: Gary L. Messing a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2017.412
a variety of approaches, to include select alloy etching, template assembly, solvent mediated aggregation, linker molecules, sol–gel, hydrothermal, carbothermal reduction, and freeze drying as a few examples.10–17 Noble metal 3-dimensional nanostructures, in particular, are desirable as electronic conductors, catalytic and biomedical materials, and electro-optical sensors.18
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