Solar Fuels: Visible‐Light‐Driven Generation of Dihydrogen at p‐Type Silicon Electrocatalysed by Molybdenum Hydrides

We show that a robust molybdenum hydride system can sustain photoelectrocatalysis of a hydrogen evolution reaction at boron‐doped, hydrogen‐terminated, p‐type silicon. The photovoltage for the system is about 600–650 mV and the current densities, which can be sustained at the photocathode in non‐catalytic and catalytic regimes, are similar to those at a photoinert vitreous carbon electrode. The kinetics of electrocatalysed hydrogen evolution at the photocathode are also very similar to those measured at vitreous carbon—evidently visible light does not significantly perturb the catalytic mechanism. Importantly, we show that the doped (1–10 Ω cm) p‐type Si can function perfectly well in the dark as an ohmic conductor and this has allowed direct comparison of the cyclic voltammetric behaviour of the response of the system under dark and illuminated conditions at the same electrode. The p‐type Si we have employed optimally harvests light energy in the 600–700 nm region and with 37 mW cm^?2 illumination in this range; the light to electrochemical energy conversion is estimated to be 2.8 %. The current yield of hydrogen under broad tungsten halide lamp illumination at 90 mW cm^?2 is (91±5) % with a corresponding chemical yield of (98±5) %.     

trans‐Bis­[2,3‐di­amino‐(R,S)‐propion­ato‐N,N′]­di­aqua­copper(II) dihydrate

The title copper complex, [Cu(dl ‐DAP)₂(H₂O)₂]·2H₂O or [Cu(C₃H₇N₂O₂)₂(H₂O)₂]·2H₂O, prepared from the non‐protein amino acid dl ‐2,3‐di­amino­propionic acid (dl ‐HDAP), has a center of symmetry and a distorted octahedral coordination, with four N atoms in equatorial positions and two water mol­ecules in apical sites. The water mol­ecule of crystallization is hydrogen bonded to the deprotonated carboxyl­ate group of the ligand.     

Passive scalar measurements in a planar mixing layer by PLIF of acetone

 Quantitative passive scalar measurements were performed in an incompressible planar mixing layer at Re _δ up to 10⁴ using planar laser-induced fluorescence of acetone seeded into one side of the layer. Probability density functions compiled from sets of images showed a preferred mixture composition, favoring the high-speed fluid, which extended across the layer. This preferred composition produced non-marching PDFs and an inflection in the average mixture fraction profile. The spatial resolution of the experiment was found to be sufficient to accurately measure the fraction of mixed fluid within the layer. The mixed fluid fraction was found to increase to an asymptotic value of 0.5 by Re _δ  ≈ 5,000, the approximate location of turbulent transition, in contrast to high Schmidt number experiments which show minimal mixing before the transition point. Received: 5 October 1999 / Accepted: 9 February 2001     

Scattering theory for hyperbolic equations of order 2m

Given self-adjoint operators H_j, on Hilbert spaces ??_j, j = 0,l, and J ∈ ?? (??₀, ??₁) (where ?? (??₀ ??₁) denotes the set of bounded linear operators from ??₀to ??₁), define the wave operators where P₀ is the projection onto the subspace for absolute continuity for H₀. We use (i) to study the scattering problem associated with a pair of equations each of the form where L is a positive, self-adjoint operator on a Hilbert space X, m is a positive integer and the α_j are distinct positive constants. Methods patterned after those of Kato are used to study two equations (that is for L = L₀ and L = L_l) each of the form (ii). We show that they are equivalent to equations of the form where each ?_k is a self-adjoint operator on an associated Hilbert space ??_k. Now suppose～he-wave operators W_±,(L₁ L₀) exist and are complete. Then we can find a J ∈ ??(H₁ H₀) such that W₊(?_l, ?₀,J) exists. In the case where L_o and L₁ have the same domain, ??₁ and ??₀ are equal as vector spaces, and under certain conditions (on L_i, i = 0, 1) ??₀ and ??₁ have equivalent norms. Assuming these conditions, let J'∈ ??(??₁' ??₀) be the identity map. We show that (with an additional assumption on L₀ and L₁) W₊(?₁?₀,J) exists andisequal to W₊(?_l,?₀, J).     

Concentration dependence of the thermal boundary resistance between dilute<Superscript>3</Superscript>He−<Superscript>4</Superscript>He solutions and sintered silver powder

We have measured the³He concentration dependence of the thermal boundary resistanceR _B between³He?⁴He dilute mixtures and submicron sintered silver between 10 and 150 mK. For concentrations greater than one percent, the results for the boundary resistance per inverse volume are insensitive to the concentration and have a magnitude similar to that predicted by the acoustic mismatch theory. For concentrations less than one percent, we observe an increase ofR _B for decreasing concentrations.