34 research outputs found
Band-Engineered LaFeO-LaNiO Thin Film Interfaces for Electrocatalysis of Water
Transition metal oxides have generated significant interest for their
potential as catalysts for the oxygen evolution reaction (OER) in alkaline
environments. Iron and nickel-based perovskite oxides have proven particularly
promising, with catalytic over-potentials rivaling precious metal catalysts
when the alignment of the valence band relative to the OER reaction potential
is tuned through substitutional doping or alloying. Here we report that
engineering of band alignment in LaFeO/LaNiO (LFO/LNO)
heterostructures via interfacial doping yields greatly enhanced catalytic
performance. Using density functional theory modeling, we predict a 0.2 eV
valence band offset (VBO) between metallic LNO and semiconducting LFO that
significantly lowers the barrier for hole transport through LFO compared to the
intrinsic material and make LFO a p-type semiconductor. Experimental band
alignment measurements using in situ X-ray photoelectron spectroscopy of
epitaxial LFO/LNO heterostructures agree quite well with these predictions,
producing a measured VBO of 0.3(1) eV. OER catalytic measurements on the same
samples in alkaline solution show an increase in catalytic current density by a
factor of ~275 compared to LFO grown on n-type Nb-doped SrTiO. These
results demonstrate the power of tuning band alignments through interfacial
band engineering for improved catalyticComment: 13 pages, 5 figures; Supplemental info: 5 pages, 5 figure
Flash-Quench Technique Employed To Study the One-Electron Reduction of Triiodide in Acetonitrile: Evidence for a Diiodide Reaction Product
Thickness Dependent OER Electrocatalysis of Epitaxial LaFeO Thin Films
Transition metal oxides have long been an area of interest for water
electrocatalysis through the oxygen evolution and oxygen reduction reactions.
Iron oxides, such as LaFeO, are particularly promising due to the
favorable energy alignment of the valence and conduction bands comprised of
Fe cations and the visible light band gap of such materials. In this
work, we examine the role of band alignment on the electrocatalytic oxygen
evolution reaction (OER) in the intrinsic semiconductor LaFeO by growing
epitaxial films of varying thicknesses on Nb-doped SrTiO. Using cyclic
voltammetry and electrochemical impedance spectroscopy, we find that there is a
strong thickness dependence on the efficiency of electrocatalysis for OER.
These measurements are understood based on interfacial band alignment in the
system as confirmed by layer-resolved electron energy loss spectroscopy and
electrochemical Mott-Schottky measurements. Our results demonstrate the
importance of band engineering for the rational design of thin film
electrocatalysts for renewable energy sources.Comment: 19 pages, 6 figures; authors Burton and Paudel contributed equally;
supplement: 11 pages, 7 figure
Plasmon-enhanced light-driven water oxidation by a dye-sensitized photoanode
Dye-sensitized photoelectrosynthesis cells (DSPECs) provide a basis for artificial photosynthesis and solar fuels production. By combining molecular chromophores and catalysts with high surface area, transparent semiconductor electrodes, a DSPEC provides the basis for light-driven conversion of water to O2 and H2 or for reduction of CO2 to carbon-based fuels. The incorporation of plasmonic cubic silver nanoparticles, with a strongly localized surface plasmon absorbance near 450 nm, to a DSPEC photoanode induces a great increase in the efficiency of water oxidation to O2 at a DSPEC photoanode. The improvement in performance by the molecular components in the photoanode highlights a remarkable advantage for the plasmonic effect in driving the 4e-/4H+ oxidation of water to O2 in the photoanode
A donor-chromophore-catalyst assembly for solar CO2 reduction
We describe here the preparation and characterization of a photocathode assembly for CO2 reduction to CO in 0.1 M LiClO4 acetonitrile. The assembly was formed on 1.0 Ī¼m thick mesoporous films of NiO using a layer-by-layer procedure based on Zr(IV)āphosphonate bridging units. The structure of the Zr(IV) bridged assembly, abbreviated as NiO|-DA-RuCP22+-Re(I), where DA is the dianiline-based electron donor (N,N,Nā²,Nā²-((CH2)3PO3H2)4-4,4ā²-dianiline), RuCP2+ is the light absorber [Ru((4,4ā²-(PO3H2CH2)2-2,2ā²-bipyridine)(2,2ā²-bipyridine))2]2+, and Re(I) is the CO2 reduction catalyst, ReI((4,4ā²-PO3H2CH2)2-2,2ā²-bipyridine)(CO)3Cl. Visible light excitation of the assembly in CO2 saturated solution resulted in CO2 reduction to CO. A steady-state photocurrent density of 65 Ī¼A cmā2 was achieved under one sun illumination and an IPCE value of 1.9% was obtained with 450 nm illumination. The importance of the DA aniline donor in the assembly as an initial site for reduction of the RuCP2+ excited state was demonstrated by an 8 times higher photocurrent generated with DA present in the surface film compared to a control without DA. Nanosecond transient absorption measurements showed that the expected reduced one-electron intermediate, RuCP+, was formed on a sub-nanosecond time scale with back electron transfer to the electrode on the microsecond timescale which competes with forward electron transfer to the Re(I) catalyst at t1/2 = 2.6 Ī¼s (kET = 2.7 Ć 105 sā1)
Flash-Quench Technique Employed To Study the One-Electron Reduction of Triiodide in Acetonitrile : Evidence for a Diiodide Reaction Product
The one-electron reduction of triiodide (I3?) by a reduced ruthenium polypyridyl compound was studied in an acetonitrile solution with the flash-quench technique. Reductive quenching of the metal-to-ligand charge-transfer excited state of [RuII(deeb)3]2+ by iodide generated the reduced ruthenium compound [RuII(deeb?)(deeb)2]+ and diiodide (I2??). The subsequent reaction of [RuII(deeb?)(deeb)2]+ with I3? indicated that I2?? was a product that appeared with a second-order rate constant of (5.1 ĆĀ± 0.2) ? 109 M?1 s?1. After correction for diffusion and some assumptions, Marcus theory predicted a formal potential of ?0.58 V (vs SCE) for the one-electron reduction of I3?. The relevance of this reaction to solar energy conversion is discussed.QC 2011122
Trading company's finansial activity analysis and effectiveness increase probabilities
Bakalaura darbÄ ir veikta mÄbeļu un mÄbeļu furnitÅ«ras tirdzniecÄ«bas uzÅÄmumu - SIA āStandard Latvijaā un āAM FurnitÅ«raā - salÄ«dzinoÅ”Ä finanÅ”u analÄ«ze.
DarbÄ ir sniegts teŠ¾rÄtisks apskats par finanÅ”u analÄ«zes veidiem, mÄrÄ·iem un uzdevumiem, par analÄ«zes kÄrtÄ«bu un pŠ¾tenciÄliem lietotÄjiem, par finanÅ”u pÄrskatiem, ir sniegts finanÅ”u analÄ«zes metožu raksturojums. Darba praktiskajÄ daÄ¼Ä ir veikta SIA ā Standard Latvijaā un SIA āAM FurnitÅ«raā bilanÄu horizontÄlÄ un vertikÄlÄ analÄ«ze, ir aprÄÄ·inÄti un izpÄtÄ«ti likviditÄtes un maksÄtspÄjas darbÄ«bas efektivitÄtes un rentabilitÄtes rÄdÄ«tÄji, kÄ arÄ« vairÄki maksÄtspÄjas prognozÄÅ”anas modeļi.
Bakalaura darba mÄrÄ·is ir veikt mÄbeļu un mÄbeļu furnitÅ«ras tirdzniecÄ«bas uzÅÄmumu finanÅ”u analÄ«zi un izstrÄdÄt priekÅ”likumus finansiÄlÄs situÄcijas uzlaboÅ”anai.
DarbÄ ir secinÄts, ka āStandard Latvijaā veiksmÄ«gÄk nekÄ āAM FurnitÅ«raā izmantoja ekonomisko uzplaukumu (2007.gads), tomÄr AMF vieglÄk pielÄgojÄs ekonomikas lejupslÄ«dei (2008. gads). KopumÄ abu uzÅÄmumu finansiÄlais stÄvoklis ir nestabils, ir liela maksÄtnespÄjas iestÄÅ”anas varbÅ«tÄ«ba.
DarbÄ izstrÄdÄÅ”anÄ tika izmantoti uzÅÄmumu finanÅ”u pÄrskatu dati par 2006-2008. gadiem. Bakalaura darbs sastÄv nŠ¾ ievada, 3 nodaļÄm, secinÄjumiem un priekÅ”likumiem. Darba apjoms ir 59 lappuses, kuras iekļauj sevÄ« 11 attÄlus un 7 tabulas. Darbam ir pievienoti 6 pielikumi.
AtslÄgvÄrdi: finanÅ”u analÄ«ze, finansiÄlais stÄvoklis, maksÄtspÄja, rÄdÄ«tÄjs, bilance, peļÅas un zaudÄjumu aprÄÄ·ins.The comparative financial analysis of furniture and furniture accessories dealers L.L.C. āStandard Latvijaā and L.L.C. āAM FurnitÅ«raā is reviewed in bachelor thesis.
The theoretical part consists of description of financial analysis aims, kinds and tasks, procedure and potential users of this service, as well as detailed description of financial analysis methods. Practical part of bachelor thesis consists of L.L.C. āStandard Latvijaā and L.L.C. āAM FurnitÅ«raā horizontal and vertical balance sheetsā analysis, calculating and analyzing liquidity, solvency, profitability ratios, as well as solvency forecasting models.
The aim of bachelor thesis is to analyze furniture dealerās financial data and to give recommendations to improve the financial situacion.
It is concluded in the thesis that L.L.C. āStandard Latvijaā had used the economic rise better than L.L.C. āAM FurnitÅ«raā in 2007, however, L.L.C. āAM FurnitÅ«ra had shown better results in 2008 than L.L.C. āStandard Latvijaā had . Companiesā financial condition is unstable, there is a high possibility of bankruptcy.
The companiesā financial statements of 2006-2008 is the basis of the bachelor thesis. The work consists of introduction, 3 chapters, conclusions and suggestions. The volume of thesis is 59 pages, which include 11 pictures and 7 tables. 6 appendixes are additionally added to the thesis.
Key words: financial analysis, financial standing, solvency, ratio, balance sheet, profit and loss statement
Visible Light Generation of Iodine Atoms and I-\u88\u92I Bonds : Sensitized I-\u88\u92 Oxidation and I3-\u88\u92 Photodissociation
Direct 355 or 532 nm light excitation of TBAI3, where TBA is tetrabutyl ammonium, in CH3CN at room temperature yields an iodine atom, I?, and an iodine radical anion, I2??. In the presence of excess iodide, the iodine atom reacts quantitatively to yield a second equivalent of I2?? with a rate constant of k = 2.5 ĆĀ± 0.4 ? 1010 M?1 s?1. The I2?? intermediates are unstable with respect to disproportionation and yield initial reactants, k = 3.3 ĆĀ± 0.1 ? 109 M?1 s?1. The coordination compound Ru(bpz)2(deeb)(PF6)2, where bpz is 2,2?-bipyrazine and deeb is 4,4?-(C2H5CO2)2-2,2?-bipyridine, was prepared and characterized for mechanistic studies of iodide photo-oxidation in acetonitrile at room temperature. Ru(bpz)2(deeb)2+ displayed a broad metal-to-ligand charge transfer (MLCT) absorption band at 450 nm with ĆĀµ = 1.7 ? 104 M?1 cm?1. Visible light excitation resulted in photoluminescence with a corrected maximum at 620 nm, a quantum yield ? = 0.14, and an excited state lifetime Ćā = 1.75 ?s from which kr = 8.36 ? 104 s?1 and knr = 5.01 ? 105 s?1 were abstracted. Arrhenius analysis of the temperature dependent excited state lifetime revealed an activation energy of ?2500 cm?1 and a pre-exponential factor of 1010 s?1, assigned to activated surface crossing to a ligand field or MLCT excited state. Steady state light excitation of Ru(bpz)2(deeb)2+ in a 20 mM TBAI acetonitrile solution resulted in ligand loss photochemistry with a quantum yield of 5 ? 10?5. The MLCT excited state was dynamically quenched by iodide with Ksv = 1.1 ? 105 M?1 and kq = 6.6 ĆĀ± 0.3 ? 1010 M?1 s?1, a value consistent with diffusion-limited electron transfer. Excited state hole transfer to iodide was quantitative but the product yield was low due to poor cage escape yields, ?CE = 0.042 ĆĀ± 0.001. Nanosecond transient absorption was used to quantify the appearance of two photoproducts [Ru(bpz?)(bpz)(deeb)]+ and I2??. The coincidence of the rate constants for [Ru(bpz?)(bpz)(deeb)]+ formation and for excited state decay indicated reductive quenching by iodide. The rate constant for the appearance of I2?? was about a factor of 3 slower than excited state decay, k = 2.4 ĆĀ± 0.2 ? 1010 M?1 s?1, indicating that I2?? was not a primary photoproduct of excited state electron transfer. A mechanism was proposed where an iodine atom was the primary photoproduct that subsequently reacted with iodide, I? + I? ? I2??. Charge recombination Ru(bpz?)(bpz)(deeb)+ + I2?? ? Ru(bpz)2(deeb)2+ + 2I? was highly favored, ?Go = ?1.64 eV, and well described by a second-order equal concentration kinetic model, kcr = 2.1 ĆĀ± 0.3 ? 1010 M?1 s?1.Qc 2011122
Visible Light Generation of Iodine Atoms and I-\u88\u92I Bonds : Sensitized I-\u88\u92 Oxidation and I3-\u88\u92 Photodissociation
Direct 355 or 532 nm light excitation of TBAI3, where TBA is tetrabutyl ammonium, in CH3CN at room temperature yields an iodine atom, I?, and an iodine radical anion, I2??. In the presence of excess iodide, the iodine atom reacts quantitatively to yield a second equivalent of I2?? with a rate constant of k = 2.5 ĆĀ± 0.4 ? 1010 M?1 s?1. The I2?? intermediates are unstable with respect to disproportionation and yield initial reactants, k = 3.3 ĆĀ± 0.1 ? 109 M?1 s?1. The coordination compound Ru(bpz)2(deeb)(PF6)2, where bpz is 2,2?-bipyrazine and deeb is 4,4?-(C2H5CO2)2-2,2?-bipyridine, was prepared and characterized for mechanistic studies of iodide photo-oxidation in acetonitrile at room temperature. Ru(bpz)2(deeb)2+ displayed a broad metal-to-ligand charge transfer (MLCT) absorption band at 450 nm with ĆĀµ = 1.7 ? 104 M?1 cm?1. Visible light excitation resulted in photoluminescence with a corrected maximum at 620 nm, a quantum yield ? = 0.14, and an excited state lifetime Ćā = 1.75 ?s from which kr = 8.36 ? 104 s?1 and knr = 5.01 ? 105 s?1 were abstracted. Arrhenius analysis of the temperature dependent excited state lifetime revealed an activation energy of ?2500 cm?1 and a pre-exponential factor of 1010 s?1, assigned to activated surface crossing to a ligand field or MLCT excited state. Steady state light excitation of Ru(bpz)2(deeb)2+ in a 20 mM TBAI acetonitrile solution resulted in ligand loss photochemistry with a quantum yield of 5 ? 10?5. The MLCT excited state was dynamically quenched by iodide with Ksv = 1.1 ? 105 M?1 and kq = 6.6 ĆĀ± 0.3 ? 1010 M?1 s?1, a value consistent with diffusion-limited electron transfer. Excited state hole transfer to iodide was quantitative but the product yield was low due to poor cage escape yields, ?CE = 0.042 ĆĀ± 0.001. Nanosecond transient absorption was used to quantify the appearance of two photoproducts [Ru(bpz?)(bpz)(deeb)]+ and I2??. The coincidence of the rate constants for [Ru(bpz?)(bpz)(deeb)]+ formation and for excited state decay indicated reductive quenching by iodide. The rate constant for the appearance of I2?? was about a factor of 3 slower than excited state decay, k = 2.4 ĆĀ± 0.2 ? 1010 M?1 s?1, indicating that I2?? was not a primary photoproduct of excited state electron transfer. A mechanism was proposed where an iodine atom was the primary photoproduct that subsequently reacted with iodide, I? + I? ? I2??. Charge recombination Ru(bpz?)(bpz)(deeb)+ + I2?? ? Ru(bpz)2(deeb)2+ + 2I? was highly favored, ?Go = ?1.64 eV, and well described by a second-order equal concentration kinetic model, kcr = 2.1 ĆĀ± 0.3 ? 1010 M?1 s?1.Qc 2011122