The pyrolysis of preceramic polymers like polysiloxanes provides the possibility of manufacturing ceramics at lower temperatures (500-1500°C) compared to the powder sintering route and of using versatile polymer shaping routes, what has attracted a growing attention in the last decade. [1] Ceramic products with different structures and functions (e.g. bulk materials, [2] composites, [3] coatings [4] and foams [5] ) were manufactured by this route and their properties (e.g. oxidation and thermal resistance, [6] electrical conductivity [7] ) can be altered by tailoring the molecular structure of the precursor and by loading the polymer with filler particles. [8] The transformation of polysiloxanes [RSiO 3/2 ] carrying hydrocarbon groups (R = methyl, phenyl, vinyl) in an inert atmosphere is well investigated and results in the formation of an amorphous silicon oxycarbide (SiOC, 800-1000°C), which decomposes to a ceramic consisting of SiC, SiO 2 and graphite at higher temperatures (1400-1500°C). [9][10][11][12] There are many examples, where a combination of a polysiloxane with a metal or a metal salt was used to prevent shrinkage, crack and pore formation of the resulting dense ceramic following the active filler controlled polymer pyrolysis concept (AFCOP). [2,13,14] Other groups used metal salts to introduce electrical conductivity or magnetic properties to SiOC materials [15] or investigated the Ni catalysed formation of carbon nanotubes in the resulting ceramics, which was observed applying temperatures beyond 800°C. [16] The size of Ni nanoparticles (< 1 wt.%) formed during pyrolysis from methylphenyl polysiloxanenickel acetate precursor came up with average diameters of 40-60 nm.A partial conversion of polysiloxane precursors below 800°C yields novel hybrid materials, which often exhibit high porosities and are therefore considered to be potential materials for adsorption and for catalyst supports. However, an adjusted design or functional testing of these hybrid materials in terms of sorption behaviour or catalytic activity has only been performed in far cases. [17] The current study focuses on the use of Ni and Pt containing polysiloxanes for preparation of highly porous hybrid materials (so called "ceramers") by inert gas pyrolysis (400-600°C) for use as adsorbent and as catalyst. In order to realize a homogeneous distribution of metallic particles at high metal contents 3-aminopropyltriethoxysilane was used for complexation of metal ions also in the combination with varying amounts of phenyltriethoxysilane. At the same time it was of interest how the different polarity of the siloxanes used for precursor preparation influenced the surface characteristic (hydrophilic/hydrophobic) of the resulting ceramers. These surface characteristics were examined in sorption experiments and first catalytic measurements revealed the catalytic activity of these ceramers.
Experimental
Synthesis of Polysiloxane Precursors and Processing of CeramersFor the synthesis of metal containing polysiloxane precursors 3-aminopropyltr...
A new type of zinc/air fuel cell comprising a Hg/Pb free Zn foam anode, a PVA/KOH electrolyte membrane and a MnO 2 /SiOCbased cathode was developed in this work. The electrochemical activity of the zinc foam and air electrode was investigated in 6 M KOH under half-cell conditions. The pristine ZnO layer of the foam matrix favoured direct oxidation of the zinc particles to zinc oxide in 6 M KOH. In the laboratory cell, a specific energy of about 500 mWh g -1 zinc was measured at 5 mA discharging current with a zinc foam, a PVA/KOH/H 2 O membrane and a MnO 2 +Vulcan/carbon paper cathode. A correlation between cell performances and porosity of the zinc foam was found. However, stability of the Zn foam and SiOC GDL materials towards KOH should be improved.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.