High-throughput screening system for catalytic hydrogen-producing materials

A high-throughput screening system and methodology were developed for libraries of hydrogen (H(2)) producing catalytic materials. The system is based on the chemo-optical properties of WO(3), which give rise to reflectance changes in the presence of H(2). Pd-coated WO(3) sensors were synthesized and examined for their hydrogen sensitivity, wavelength-dependent reflectance, and performance in the presence of water vapor. For high-throughput screening, a polypropylene reactor block was designed and constructed to house 8 x 12 catalyst libraries deposited as thin films. When the library and reactor block are assembled together, 96 independent microreactor units are formed. A large-area Pd/WO(3) sensor film covers and seals all microreactors, forming a 96-element 2-D H(2) sensor array. As H(2) is produced differentially across the library, the reflectance changes of the Pd/WO(3) film are monitored by reflectivity sensors that scan the surface every 30 s. The time-dependent changes in reflectance indicate relative rates of H(2) production. A library of cathode electrocatalysts was synthesized from Ti, Pt, Ni, Au, Pd, Al, Ag, Ge, and mixtures thereof to demonstrate the H(2) high-throughput screening system. The results of the electrolytic screening are in agreement with expected literature trends: mixtures of Ni and samples containing Pt and Pd generated H(2) at the greatest rates, while Ge- and Ti-based materials were the least effective electrocatalysts. A mixture of 80% Al and 20% Pt was found to have the highest rate of H(2) production. This high-throughput screening system is applicable in a variety of catalytic screening applications where hydrogen is the desired product.     

Parallel synthesis and characterization of photoelectrochemically and electrochromically active tungsten-molybdenum oxides

Single phase tungsten-molybdenum mixed oxide films (W(1-x)Mo(x)O(3)) were successfully synthesized by automated parallel electrodeposition, and distinct structural changes were observed as a function of composition. A monoclinic structure (beta-phase) was observed in mixed oxides with less than 90% Mo, and above 90% Mo, orthorhombic structure (alpha-phase) was identified.     

Catalytic activity of supported Au nanoparticles deposited from block copolymer micelles

Quasi-ordered, highly dispersed, gold nanoclusters of tightly controlled particle size were synthesized by dip-coating substrates with gold precursors encapsulated by block-copolymer micelles. By this method, gold particles (4.8 +/- 1.3 nm) were deposited on ITO-coated glass and shown to be catalytically active for electro-oxidation of carbon monoxide. XPS confirmed the catalytically active particles were predominantly Au0; however, a large fraction existed as Au3+. Whereas bulk gold is inert, these results demonstrate that catalytically active Au nanoparticles can be derived from micelle encapsulation.     

Influence of a polar near-neighbor on incipient proton transfer in a strongly hydrogen bonded complex

Rotational spectroscopy and ab initio calculations have been used to characterize the complexes H(3)N-HF and H(3)N-HF-HF in the gas phase. H(3)N-HF is a C(3v) symmetric, hydrogen bonded system with an NF distance of 2.640(21) A and an N...H hydrogen bond length of 1.693(42) A. The H(3)N-HF-HF complex, on the other hand, forms a six-membered HN-HF-HF ring, in which both the linear hydrogen bond in the H(3)N-HF moiety and the F-H-F angle of (HF)(2) are perturbed relative to those in the corresponding dimers. The N...F and F...F distances in the trimer are 2.4509(74) A and 2.651(11) A, respectively. The N...H hydrogen bond length in H(3)N-HF-HF is 1.488(12) A, a value which is 0.205(54) A shorter than that in H(3)N-HF. Similarly, the F...F distance, 2.651(11) A, is 0.13(2) A shorter than that in (HF)(2). Counterpoise-corrected geometry optimizations are presented, which are in good agreement with the experimental structures for both the dimer and trimer, and further characterize small, but significant, changes in the NH(3) and HF subunits upon complexation. Analysis of internal rotation in the spectrum of H(3)N-HF-HF gives the potential barrier for internal rotation of the NH(3) unit, V(3), to be 118(2) cm(-1). Ab initio calculations reproduce this number to within 10% if the monomer units and the molecular frame are allowed to fully relax as the internal rotation takes place. The binding energies of H(3)N-HF and H(3)N-HF-HF, calculated at the MP2/aug-cc-pVTZ level and corrected for basis set superposition error are 12.3 and 22.0 kcal/mol, respectively. Additional energy calculations have been performed to explore the lowest frequency vibration of H(3)N-HF-HF, a ring-opening motion that increases the NFF angle. The addition of one HF molecule to H(3)N-HF represents the first step of microsolvation of a hydrogen bonded complex and the results of this study demonstrate that a single, polar near-neighbor has a significant influence on the extent of proton transfer across the hydrogen bond. As measured using the proton-transfer parameter rho(PT), previously defined by Kurnig and Scheiner [Int. J. Quantum Chem., Quantum Biol. Symp. 1987, 14, 47], the degree of proton transfer in H(3)N-HF-HF is greater than that in either (CH(3))(3)N-HF or H(3)N-HCl but less than that in (CH(3))(3)N-HCl.     

Evaluation and optimization of electron capture dissociation efficiency in fourier transform ion cyclotron resonance mass spectrometry

Electron capture dissociation (ECD) efficiency has typically been lower than for other dissociation techniques. Here we characterize experimental factors that limit ECD and seek to improve its efficiency. Efficiency of precursor to product ion conversion was measured for a range of peptide (∼15% efficiency) and protein (∼33% efficiency) ions of differing sizes and charge states. Conversion of precursor ions to products depends on electron irradiation period and maximizes at ∼5–30 ms. The optimal irradiation period scales inversely with charge state. We demonstrate that reflection of electrons through the ICR cell is more efficient and robust than a single pass, because electrons can cool to the optimal energy for capture, which allows for a wide range of initial electron energy. Further, efficient ECD with reflected electrons requires only a short (∼500 μs) irradiation period followed by an appropriate delay for cooling and interaction. Reflection of the electron beam results in electrons trapped in or near the ICR cell and thus requires a brief (∼50 μs) purge for successful mass spectral acquisition. Further electron irradiation of refractory precursor ions did not result in further dissociation. Possibly the ion cloud and electron beam are misaligned radially, or the electron beam diameter may be smaller than that of the ion cloud such that remaining precursor ions do not overlap with the electron beam. Several ion manipulation techniques and use of a large, movable dispenser cathode reduce the possibility that misalignment of the ion and electron beams limits ECD efficiency.     

Unprecedented alkene stereocontrol in the Claisen rearrangement of cyclic bis-allylic esters

The Ireland and ester enolate Claisen rearrangements of tertiary substituted bis-allylic esters derived from cyclohexenones afford pentenoic acids that possess tri- and tetrasubstituted alkylidenes with unprecedented levels of stereoselectivity. In some cases the higher energy exocyclic alkene is the major product. [reaction: see text]     

NiFe-oxide electrocatalysts for the oxygen evolution reaction on Ti doped hematite photoelectrodes

Nickel iron binary oxide electrocatalysts prepared from different precursors were evaluated to facilitate the oxygen evolution reaction (OER) on semiconducting metal-oxide photoelectrodes. The electrocatalysts deposited from Ni(II) and Ni(II)Fe(II) precursors had the highest activity for OER, however, their presence on the surface of the Ti doped hematite photoelectrode decreased the incident photon-to-current efficiency (IPCE) of the photoelectrode for water splitting in an alkaline electrolyte. In contrast, the NiFe-oxide deposited from the Ni(II)–Fe(III) precursor which had a lower OER activity was found to increase the IPCE of the photoelectrode by as much as a factor of 5.     

Passive damping enhancement of a two-degree-of-freedom system through a strongly nonlinear two-degree-of-freedom attachment

This work reports on the first experimental study of the broadband targeted energy transfer properties of a two-degree-of-freedom (two-DOF) essentially nonlinear energy absorber. In particular, proper design of the absorber allows for an extended range of energy over which it serves to significantly enhance the damping observed in the structural system to which it is attached. Comparisons of computational and experimental results validate the proposed design as a means of drastically enhancing the damping properties of a structure by passive broadband targeted energy transfers to a strongly nonlinear, multidegree-of-freedom attachment.