A Nanowire-Nanoparticle Cross-Linking Approach to Highly Porous Electrically Conducting Solids

摘要

As a result of their high surface-to-volume ratios, porous inorganic solids have found technological applications as molecular sieves, ion exchangers, and catalysts.[1] Recent research in the area of porous solids has also led to materials that combine high surface areas with electrical conductivity.[2] These porous conductors are desirable components in batteries, sensors, fuel cells, capacitors,[3] and electrocatalysts.[4] Porous conductors are typically synthesized by chemical linkage of electrically conductive colloidal building blocks (e.g. V2O5)[5], [6] and their precursors (e.g. resorcine),[7] or by applying conductive coatings (e.g. RuO2)[4] to existing porous solids. Another approach is to introduce mobile ions into porous structures.[8], [9] We describe herein a novel approach to metallic porous solids that is based on cross-linking LiMo3Se3 nanowires with Ag nanoparticles. LiMo3Se3 nanowires (for structure see bottom of Figure 1) can be obtained easily by exfoliation of the corresponding Chevrel phase.[10], [11] Owing to their metallic properties[12], [13] the nanowires have been investigated as components in electrically conducting composites,[14]-[17] as electrode materials for Li-battery applications,[18] and as analyte-detection devices in nanowire-film chemiresistors.[19] When an aqueous dispersion of LiMo3Se3 nanowires is added to an aqueous dispersion of citrate-coated silver nanoparticles (15? nm), a gel forms within minutes (Figure 1). Further analysis (see below) shows that the gel is composed of silver nanoparticles that connect nanowire bundles through presumably covalent bonds between the silver and selenide ions. Similar covalent interactions occur in LiMo3Se3-Au and LiMo3Se3-CdSe composites.[17] These AgSe bonds form within seconds after mixing the reagents, as proven by the fact that centrifugation of a fresh reaction mixture leads to complete sedimentation of all inorganic materials whereas separate dispersions of silver nanoparticles and LiMo3Se3 nanowires are stable for weeks under similar conditions.