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Caltech Authors (170.931 recursos)

Repository of works by Caltech published authors.

Group = CCI Solar Fuels

Mostrando recursos 1 - 20 de 117

  1. End of an era: Lessons learned from 10 years of outreach at a NSF-funded center

    Schuttlefield Christus, Jennifer; DeBoever, Michelle
    Since 2005, the Center for Chem. Innovation (CCI) Solar Fuels has focused on one of the "holy-grails" of 21st Century chem. - the efficient and economical conversion of solar energy into stored chem. fuel, where researchers investigate the crit. science underpinning the solar-driven decompn. of water into hydrogen and oxygen. The CCI's outreach program has been deeply integrated into the research mission of the Center. Specifically, the outreach program developed three main themes. The first is real-time research experiences aimed at discovering inexpensive, stable oxide semiconductors that can efficiently photoelectrolyze water to a useable fuel, hydrogen. This manifested in three...

  2. Phase Directing Ability of an Ionic Liquid Solvent for the Synthesis of HER-Active Ni_2P Nanocrystals

    Roberts, Emily J.; Read, Carlos G.; Lewis, Nathan S.; Brutchey, Richard L.
    An ionic liquid (IL) solvent was used to synthesize small, phase-pure nickel phosphide (Ni_2P) nanocrystals. In contrast, under analogous reaction conditions, substitution of the IL for the common high-boiling organic solvent 1-octadecene (ODE) results in phase-impure nanocrystals. The 5 nm Ni_2P nanocrystals prepared in IL were electrocatalytically active toward the hydrogen evolution reaction. The synthesis in IL was also extended to alloyed Ni_(2–x)Co_xP nanocrystals, where 0.5 ≤ x ≤ 1.5.

  3. Solar Army: Incorporating real-time research into outreach efforts

    Schuttlefield Christus, Jennifer; DeBoever, Michelle
    The Solar Army is the international outreach effort for the NSF- funded Center for Chem. Innovation Solar Fuels based at the California Institute of Technol. The CCI Solar Fuel research focuses on one of the "holy- grails" of 21st Century chem. - the efficient and economical conversion of solar energy into stored chem. fuel. CCI Solar investigators are targeting the crit. science underpinning the solar- driven decompn. of water into hydrogen and oxygen. The Solar Army utilizes three outreach kits to educate participants on solar energy conversion and provide students with an opportunity to participate in real- time research searching for solar water- splitting catalysts....

  4. Iron Is the Active Site in Nickel/Iron Water Oxidation Electrocatalysts

    Hunter, Bryan M.; Winkler, Jay R.; Gray, Harry B.
    Efficient catalysis of the oxygen-evolution half-reaction (OER) is a pivotal requirement for the development of practical solar-driven water splitting devices. Heterogeneous OER electrocatalysts containing first-row transition metal oxides and hydroxides have attracted considerable recent interest, owing in part to the high abundance and low cost of starting materials. Among the best performing OER electrocatalysts are mixed Fe/Ni layered double hydroxides (LDH). A review of the available experimental data leads to the conclusion that iron is the active site for [NiFe]-LDH-catalyzed alkaline water oxidation.

  5. Trapping an Iron(VI) Water-Splitting Intermediate in Nonaqueous Media

    Hunter, Bryan M.; Thompson, Niklas B.; Müller, Astrid M.; Rossman, George R.; Hill, Michael G.; Winkler, Jay R.; Gray, Harry B.
    We report in situ spectroscopic measurements in nonaqueous media designed to trap an exceptionally strong oxidant generated electrochemically from an iron-containing nickel layered double hydroxide ([NiFe]-LDH) material. Anodic polarization of this material in acetonitrile produces metal-oxo vibrational spectroscopic signatures along with an extremely narrow near-infrared luminescence peak that strongly indicate that the reactive intermediate is cis-dioxo-iron(VI). Chemical trapping experiments reveal that addition of H_2O to the polarized electrochemical cell produces hydrogen peroxide; and, most importantly, addition of HO– generates oxygen. Repolarization of the electrode restores the iron(VI) spectroscopic features, confirming that the high-valent oxo complex is active in the electrocatalytic...

  6. Triphenylsulfonium topophotochemistry

    Despagnet-Ayoub, E.; Kramer, W. W.; Sattler, W.; Sattler, A.; LaBeaume, P. J.; Thackeray, J. W.; Cameron, J. F.; Cardolaccia, T.; Rachford, A. A.; Winkler, J. R.; Gray, H. B.
    The products from the 193 nm irradiation of triphenylsulfonium nonaflate (TPS) embedded in a poly(methyl methacrylate) (PMMA) film have been characterized. The analysis of the photoproduct formation was performed using chromatographic techniques including HPLC, GPC and GC-MS as well as UV-vis and NMR spectroscopic methods. Two previously unreported TPS photoproducts, triphenylene and dibenzothiophene, were detected; additionally, GPC and DOSY-NMR spectroscopic analyses after irradiation suggested that TPS fragments had been incorporated into the polymer film. The irradiation of acetonitrile solutions containing 10% w/v PMMA and 1% w/v TPS in a 1 cm-path-length cuvette showed only a trace amount of triphenylene or...

  7. Triphenylsulfonium topophotochemistry

    Despagnet-Ayoub, E.; Kramer, W. W.; Sattler, W.; Sattler, A.; LaBeaume, P. J.; Thackeray, J. W.; Cameron, J. F.; Cardolaccia, T.; Rachford, A. A.; Winkler, J. R.; Gray, H. B.
    The products from the 193 nm irradiation of triphenylsulfonium nonaflate (TPS) embedded in a poly(methyl methacrylate) (PMMA) film have been characterized. The analysis of the photoproduct formation was performed using chromatographic techniques including HPLC, GPC and GC-MS as well as UV-vis and NMR spectroscopic methods. Two previously unreported TPS photoproducts, triphenylene and dibenzothiophene, were detected; additionally, GPC and DOSY-NMR spectroscopic analyses after irradiation suggested that TPS fragments had been incorporated into the polymer film. The irradiation of acetonitrile solutions containing 10% w/v PMMA and 1% w/v TPS in a 1 cm-path-length cuvette showed only a trace amount of triphenylene or...

  8. Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+)

    Pižl, Martin; Hunter, Bryan M.; Greetham, Gregory M.; Towrie, Michael; Záliš, Stanislav; Gray, Harry B.; Vlček, Antonín
    Binuclear complexes of d^8 metals (Pt^(II), Ir^I, Rh^I, ) exhibit diverse photonic behavior including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy-, electron-, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M-M bonding is strengthened upon dσ *→pσ excitation. We report the bridging ligand dynamics of Ir_2(1,8-diisocyanomenthane)_4^(2+) (Ir(dimen)), investigated by fs-ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000-2300 cm^(-1). The ν(C≡N) IR band of the singlet and triplet dσ*pσ excited states is shifted by -22 and...

  9. Ultrafast Wiggling and Jiggling: Ir_2(1,8-diisocyanomenthane)_4^(2+)

    Pižl, Martin; Hunter, Bryan M.; Greetham, Gregory M.; Towrie, Michael; Záliš, Stanislav; Gray, Harry B.; Vlček, Antonín
    Binuclear complexes of d^8 metals (Pt^(II), Ir^I, Rh^I,) exhibit diverse photonic behavior, including dual emission from relatively long-lived singlet and triplet excited states, as well as photochemical energy, electron, and atom transfer. Time-resolved optical spectroscopic and X-ray studies have revealed the behavior of the dimetallic core, confirming that M–M bonding is strengthened upon dσ* → pσ excitation. We report the bridging ligand dynamics of Ir2(1,8-diisocyanomenthane)_4^(2+)(Ir(dimen)), investigated by fs–ns time-resolved IR spectroscopy (TRIR) in the region of C≡N stretching vibrations, ν(C≡N), 2000–2300 cm^(–1). The ν(C≡N) IR band of the singlet and triplet dσ*pσ excited states is shifted by −22 and −16...

  10. Photoelectrochemical Performance of BiVO_4 Photoanodes Integrated with [NiFe]-Layered Double Hydroxide Nanocatalysts

    Sinclair, Timothy S.; Gray, Harry B.; Müller, Astrid M.
    We immobilized laser-made nickel iron layered double hydroxide ([NiFe]-LDH) nanocatalysts on BiVO_4 photoanodes. We compared photoelectrochemical performance of integrated [NiFe]-LDH–BiVO_4 photoanodes in sulfite-free aqueous electrolyte with photocurrent generation of neat BiVO_4 photoanodes in aqueous electrolyte with sulfite added as sacrificial hole acceptor. We optimized catalyst mass loading, which is a tradeoff between most efficient depletion of photogenerated holes that drive catalytic turnover and parasitic light absorption by the catalyst particles. We also mitigated nanocatalyst aggregation on the BiVO_4 surface by a surfactant that selectively ligated the catalysts or by dispersing the catalyst suspension more rapidly on the photoanode surface. Our...

  11. Electrochemistry in ionic liquids: Case study of a manganese corrole

    McNicholas, Brendon J.; Blumenfeld, Carl; Kramer, Wesley W.; Grubbs, Robert H.; Winkler, Jay R.; Gray, Harry B.
    Voltammetry of [5,10,15-tris(pentafluorophenylcorrole)]Mn(III) was investigated in four different ionic liquids (ILs): 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIm-TFSI); 1-ethyl-3-methylimidazolium ethylsulfate (EMIm-EtOSO_3); 1-ethyl-3-methylimidazolium triflate (EMIm-OTf); and 1-ethyl-3-methylimidazolium tetracyanoborate (EMIm-TCB). We found that Mn^(IV/III) E_(1/2) values depend on IL counter anion: OTf–< EtOSO_3− < TFSI− < TCB−. In EMIm-TCB and BMIm- TFSI, reversible, diffusion-controlled MnIV/III reactions occurred, as evidenced in each case by the ratio of anodic to cathodic diffusion coefficients over a range of scan rates. Axial coordination was evidenced by a cathodic to anodic diffusion coefficient ratio greater than one, an increasing cathodic to anodic peak current ratio with increasing scan rate, and a...

  12. Two-photon spectroscopy of tungsten(0) arylisocyanides using nanosecond-pulsed excitation

    Takematsu, Kana; Wehlin, Sara A. M.; Sattler, Wesley; Winkler, Jay R.; Gray, Harry B.
    The two-photon absorption (TPA) cross sections (δ) for tungsten(0) arylisocyanides (W(CNAr)6) were determined in the 800–1000 nm region using two-photon luminescence (TPL) spectroscopy. The complexes have high TPA cross sections, in the range 1000–2000 GM at 811.8 nm. In comparison, the cross section at 811.8 nm for tris-(2,2′-bipyridine)ruthenium(II), [Ru(bpy)_3]^(2+), is 7 GM. All measurements were performed using a nanosecond-pulsed laser system.

  13. Two-photon spectroscopy of tungsten(0) arylisocyanides using nanosecond-pulsed excitation

    Takematsu, Kana; Wehlin, Sara A. M.; Sattler, Wesley; Winkler, Jay R.; Gray, Harry B.
    The two-photon absorption (TPA) cross sections (δ) for tungsten(0) arylisocyanides (W(CNAr)6) were determined in the 800–1000 nm region using two-photon luminescence (TPL) spectroscopy. The complexes have high TPA cross sections, in the range 1000–2000 GM at 811.8 nm. In comparison, the cross section at 811.8 nm for tris-(2,2′-bipyridine)ruthenium(II), [Ru(bpy)_3]^(2+), is 7 GM. All measurements were performed using a nanosecond-pulsed laser system.

  14. Two-photon spectroscopy of tungsten(0) arylisocyanides using nanosecond-pulsed excitation

    Takematsu, Kana; Wehlin, Sara A. M.; Sattler, Wesley; Winkler, Jay R.; Gray, Harry B.
    The two-photon absorption (TPA) cross sections (δ) for tungsten(0) arylisocyanides (W(CNAr)6) were determined in the 800–1000 nm region using two-photon luminescence (TPL) spectroscopy. The complexes have high TPA cross sections, in the range 1000–2000 GM at 811.8 nm. In comparison, the cross section at 811.8 nm for tris-(2,2′-bipyridine)ruthenium(II), [Ru(bpy)_3]^(2+), is 7 GM. All measurements were performed using a nanosecond-pulsed laser system.

  15. The mechanism for catalytic hydrosilylation by bis(imino)pyridine iron olefin complexes supported by broken symmetry density functional theory

    Lam, Yan Choi; Nielsen, Robert J.; Goddard, William A., III; Dash, Aswini K.
    Density functional theory (DFT, B3LYP-D3 with implicit solvation in toluene) was used to investigate the mechanisms of olefin hydrosilylation catalyzed by PDI(Fe) (bis(imino)pyridine iron) complexes, where PDI = 2,6-(ArN CMe)_2(C_5H_3N) with Ar = 2,6-R_2-C_6H_3. We find that the rate-determining step for hydrosilylation is hydride migration from Et3SiH onto the Fe-bound olefin to form (PDI)Fe(alkyl)(SiEt_3). This differs from the mechanism for the Pt Karstedt catalyst in that there is no prior Si–H oxidative addition onto the Fe center. (PDI)Fe(alkyl)(SiEt_3) then undergoes C–Si reductive elimination to form (PDI)Fe, which coordinates an olefin ligand to regenerate the resting state (PDI)Fe(olefin). In agreement with...

  16. The mechanism for catalytic hydrosilylation by bis(imino)pyridine iron olefin complexes supported by broken symmetry density functional theory

    Lam, Yan Choi; Nielsen, Robert J.; Goddard, William A., III; Dash, Aswini K.
    Density functional theory (DFT, B3LYP-D3 with implicit solvation in toluene) was used to investigate the mechanisms of olefin hydrosilylation catalyzed by PDI(Fe) (bis(imino)pyridine iron) complexes, where PDI = 2,6-(ArN CMe)_2(C_5H_3N) with Ar = 2,6-R_2-C_6H_3. We find that the rate-determining step for hydrosilylation is hydride migration from Et3SiH onto the Fe-bound olefin to form (PDI)Fe(alkyl)(SiEt_3). This differs from the mechanism for the Pt Karstedt catalyst in that there is no prior Si–H oxidative addition onto the Fe center. (PDI)Fe(alkyl)(SiEt_3) then undergoes C–Si reductive elimination to form (PDI)Fe, which coordinates an olefin ligand to regenerate the resting state (PDI)Fe(olefin). In agreement with...

  17. Membranes for artificial photosynthesis

    Chabi, Sakineh; Papadantonakis, Kimberly M.; Lewis, Nathan S.; Freund, Michael S.
    Membrane-based architectures enable optimization of charge transport and electrochemical potential gradients in artificial photosynthesis. Spatial integration of the membrane-bound components reduces the impact of charge recombination and can reduce electrical resistances associated with ionic and electronic transport processes. In addition to eliminating the need for external electrical circuits, a membrane-based architecture also ensures separation of energetic products, thereby preventing the formation of potentially dangerous fuel/oxidant mixtures. Membrane-based structures may also be coupled with other devices, such as perovskite-based solar cells, to further benefit solar fuel production. This review discusses the key roles that various different types of membranes play in...

  18. Conservation of vibrational coherence in ultrafast electronic relaxation: The case of diplatinum complexes in solution

    Monni, Roberto; Auböck, Gerald; Kinschel, Dominik; Aziz-Lange, Kathrin M.; Gray, Harry B.; Vlček, Antonín; Chergui, Majed
    We report the results of ultrafast transient absorption studies of tetrakis(μ-pyrophosphito)diplatinate(II), [Pt_2(μ-P_2O_5H_2)_4]^(4−) (Pt(pop)) and its perfluoroborated derivative [Pt_2(μ-P_2O_5(BF_2)_4]^(4−) (Pt(pop-BF_2)) in water and acetonitrile upon excitation of high lying (<300 nm) UV absorption bands. We observe an ultrafast relaxation channel from high lying states to the lowest triplet state that partly (Pt(pop) in H_2O, Pt(pop-BF_2)) or fully (Pt(pop) in MeCN) bypasses the lowest singlet excited state. As a consequence, vibrational wave packets are detected in the lowest triplet state and/or the lowest excited singlet of both complexes, even though the electronic relaxation cascade spans ca. 2 and 1.3 eV, respectively. In...

  19. Electronic structures and photophysics of d^8-d^8 complexes

    Gray, Harry B.; Záliš, Stanislav; Vlček, Antonín
    Research on d^8-d^8 complexes is being actively pursued, owing, in part, to newly developed time-resolved optical, IR, and X-ray methods that directly interrogate bonding changes upon excitation. Our review covers work on the ground- and electronic excited states, as well as the oxidized and reduced forms, of these complexes. Recent experimental and theoretical results add a new chapter to the rich history of d^8-d^8 spectroscopic and chemical behavior.

  20. A Mechanistic Study of the Oxidative Reaction of Hydrogen-Terminated Si(111) Surfaces with Liquid Methanol

    Plymale, Noah T.; Dasog, Mita; Brunschwig, Bruce S.; Lewis, Nathan S.
    H–Si(111) surfaces have been reacted with liquid methanol (CH_3OH) in the absence or presence of a series of oxidants and/or illumination. Oxidant-activated methoxylation of H–Si(111) surfaces was observed in the dark after exposure to CH_3OH solutions that contained the one-electron oxidants acetylferrocenium, ferrocenium, or 1,1’-dimethylferrocenium. The oxidant-activated reactivity toward CH_3OH of intrinsic and n-type H–Si(111) surfaces increased upon exposure to ambient light. The results suggest that oxidant-activated methoxylation requires that two conditions be met: (1) the position of the quasi-Fermi levels must energetically favor oxidation of the H–Si(111) surface and (2) the position of the quasi-Fermi levels must energetically favor...

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