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Facile synthesis: Pt nanosponges, nanonetworks, and nanodendrites (see figure) are synthesized through a unique galvanic replacement reaction between Te nanowires and PtCl(6) (2-) ions in the presence of sodium dodecyl sulfate. The three Pt nanomaterials all have large active surface areas and highly electrocatalytic activities for the oxidation of methanol.In this paper, we report a simple approach for the preparation of various porous Pt nanomaterials (NMs) in aqueous solution. Employing different temperatures and concentrations of sodium dodecyl sulfate (SDS), we obtained Pt nanosponges, Pt nanonetworks, and Pt nanodendrites from the reduction of PtCl(6) (2-) ions via galvanic replacement reactions with Te nanowires (length: 879 nm; diameter: 19 nm). At ambient temperature, Pt nanosponges and Pt nanodendrites formed selectively in the presence of SDS at concentrations of <10 mM and>50 mM, respectively. At elevated reaction temperatures, we obtained Pt nanonetworks and Pt nanodendrites in the presence of SDS at concentrations of <10 mM and >50 mM, respectively. Transmission electron microscopy images revealed that these Pt NMs were all composed of one dimensional Pt nanostructures having widths of 3.0+/-1.0 nm and lengths of 17.0+/-4.8 nm. Cyclic voltammetry data indicated that the as-prepared Pt nanonetworks, nanosponges, and nanodendrites possessed large electrochemically active surface areas (77.0, 70.4, and 41.4 m(2) g(-1), respectively). For the electrocatalytic oxidation of methanol, the ratio of the forward oxidation peak current (I(f)) to the backward peak current (I(b)) of the Pt nanodendrites, nanosponges, and nanonetworks were all high (I(f)/I(b)=2.88, 2.66, and 2.16, respectively). These three NMs exhibit greater electrocatalytic activities and excellent tolerance toward poisoning species for the oxidation of methanol when compared with the performance of standard Pt NMs.

By direct numerical solution of Maxwell's equations and the semiconductor drift-diffusion equations, we demonstrate solar power conversion efficiencies in the 29%−30% range in crystalline-silicon photonic-crystal solar cells. These 3 − 12 µm thick photonic crystals, consisting of wavelength-scale inverted-pyramid arrays, absorb sunlight considerably in excess of the Lambertian limit due to wave-interference based light-trapping. It is suggested that the resulting optimized balance between bulk-Auger recombination and solar absorption occurs for a silicon thickness of 10 µm, in contrast to previous estimates of over 100 µm. Optimized n + pp + doping profiles involving low p−doping throughout most of the bulk and thin n + and p + −doping at the emitter and base regions yield ideal electronic response. For solar absorption restricted to the 300 − 1100 nm range, we obtain a short circuit current of 42.5 mA/cm 2 , an open circuit voltage of nearly 0.8 V and a fill-factor of about 87%, provided that the surface recombination velocities are below 100 cm/s. Including solar absorption in the 1100 − 1200 nm range through electronic bandgap narrowing and the Urbach optical absorption edge, our wave-interference-based light-trapping enables an additional photo-current density of 1.09 mA/cm 2 for an overall power conversion efficiency of 30%. It is shown that under solar concentration by factors of 20 and 150, the power conversion efficiencies are enhanced to 32.5% and 33.5%, respectively.

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