2006 Energy conversion V 1650Study of Porous Silicon Nanostructures as Hydrogen Reservoirs. -The hydrogen content in porous silicon nanostructures is quantitatively characterized by attenuated total reflection infrared spectroscopy and temperature-programmed desorption spectroscopy. Maximal hydrogen concentration of 66 mmol/g is observed in nanoporous layers with high (>95%) porosity consisting of nanocrystallites with dimensions of about 2 nm. Mass energy density that can be potentially obtained from this amount of hydrogen through a low-temperature fuel cell is estimated to be about 2176 Wh/kg. It is suggested that the hydrogenated porous silicon nanostructures can be used as hydrogen source for Si-based fuel cells operating as energy suppliers in various portable devices. -(LYSENKO*, V.; BIDAULT, F.; ALEKSEEV, S.; ZAITSEV, V.; BARBIER, D.; TURPIN, C.; GEOBALDO, F.; RIVOLO, P.; GARRONE, E.; J.
Electrochemical dissolution of highly doped (ρ ∼ 1 mΩ•cm, n-type) polycrystalline 3C-SiC in HF/H 2 O and HF/H 2 O/ethanol solutions allowed production of porous silicon carbide (por-SiC) and soluble carbon fluorooxide nanoparticles as a byproduct. The por-SiC is a crystalline material with large pore volume, surface area close to 100 m 2 g −1 , and open mesoporous structure. The surface of por-SiC is covered with a thin carbon-enriched layer, bearing carboxylic acid groups. Depending on the SiC resistivity, etchant composition, and current density, three different types of por-SiC morphology, namely, a macroporous tubular, mesoporous hierarchical, and mesoporous filamentary were revealed. A qualitative physical model of SiC electrochemical dissolution, based on the phenomena of quantum confinement, charge carriers trapping onto the surface defects, and the surface passivation, was proposed, and the model successfully interpreted the dependencies of por-SiC morphology and material balance on the etching conditions. The por-SiC is anticipated to be a prospective material for catalytic, nanofiltration, and sensing applications.
The photoacoustic method with piezoelectric detection for the simultaneous evaluation of the thermophysical properties is proposed. The approach is based on the settling of an additional heat sink for redistribution of heat fluxes deposited on the sample surface. Firstly, the approach was tested on the porous silicon with welldefined morphology and well-studied properties. Then, heat capacity and thermal conductivity of silicon nanowires arrays have been investigated by recovering the experimental data through numerical simulations. The decrease of heat capacity and effective thermal conductivity of the samples upon increasing thickness and porosity of the sample is observed. Such behavior could be caused by the increase of the structure heterogeneity. In particular, this can be related to larger disorder (increased density of broken nanowires and larger porosity) that appears during the etching process of the thick layers.
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