| 1. |
|
|
| 2. |
- Aster, Alexander, et al.
(författare)
-
Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes
- 2019
-
Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:21, s. 5582-5588
-
Tidskriftsartikel (refereegranskat)abstract
- Electron and proton transfer reactions of diiron complexes [Fe(2)adt(CO)(6)] (1) and [Fe(2)adt(CO)(4)(PMe3)(2)] (4), with the biomimetic azadithiolate (adt) bridging ligand, have been investigated by real-time IR- and UV-vis-spectroscopic observation to elucidate the role of the adt-N as a potential proton shuttle in catalytic H-2 formation. Protonation of the one-electron reduced complex, 1(-), occurs on the adt-N yielding 1H and the same species is obtained by one-electron reduction of 1H(+). The preference for ligand vs. metal protonation in the Fe-2(i,0) state is presumably kinetic but no evidence for tautomerization of 1H to the hydride 1Hy was observed. This shows that the adt ligand does not work as a proton relay in the formation of hydride intermediates in the reduced catalyst. A hydride intermediate 1HHy(+) is formed only by protonation of 1H with stronger acid. Adt protonation results in reduction of the catalyst at much less negative potential, but subsequent protonation of the metal centers is not slowed down, as would be expected according to the decrease in basicity. Thus, the adtH(+) complex retains a high turnover frequency at the lowered overpotential. Instead of proton shuttling, we propose that this gain in catalytic performance compared to the propyldithiolate analogue might be rationalized in terms of lower reorganization energy for hydride formation with bulk acid upon adt protonation.
|
|
| 3. |
- Brown, Allison, et al.
(författare)
-
Ultrafast Electron Transfer between Dye and Catalyst on a Mesoporous NiO Surface
- 2016
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 26, s. 8060-8063
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The combination of molecular dyes and catalysts with semiconductors into dye-sensitized solar fuel devices (DSSFDs) requires control of efficient interfacial and surface charge transfer between the components. The present study reports on the light-induced electron transfer processes of p-type NiO films cosensitized with coumarin C343 and a bioinspired proton reduction catalyst, [FeFe](mcbdt)(CO)(6) (mcbdt = 3-carboxybenzene-1,2-dithiolate). By transient optical spectroscopy we find that ultrafast interfacial electron transfer (tau approximate to 200 fs) from NiO to the excited C343 ("hole injection") is followed by rapid (t(1/2) approximate to 10 ps) and efficient surface electron transfer from C343 to the coadsorbed [FeFe] (mcbdt)(CO)(6). The reduced catalyst has a clear spectroscopic signature that persists for several tens of microseconds, before charge recombination with NiO holes occurs. The demonstration of rapid surface electron transfer from dye to catalyst on NiO, and the relatively long lifetime of the resulting charge separated state, suggests the possibility to use these systems for photocathodes on. DSSFDs.
|
|
| 4. |
|
|
| 5. |
- Jain, Sagar Motilal, et al.
(författare)
-
Frustrated Lewis pair-mediated recrystallization of CH3NH3PbI3 for improved optoelectronic quality and high voltage planar perovskite solar cells
- 2016
-
Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 9:12, s. 3770-3782
-
Tidskriftsartikel (refereegranskat)abstract
- Films of the hybrid lead halide perovskite CH3NH3PbI3 were found to react with pyridine vapor at room temperature leading to complete bleaching of the film. In dry air or nitrogen atmosphere recrystallization takes place, leading to perovskite films with markedly improved optical and photovoltaic properties. The physical and chemical origin of the reversible bleaching and recrystallization mechanism was investigated using a variety of experimental techniques and quantum chemical calculations. The strong Lewis base pyridine attacks the CH3NH3PbI3. The mechanism can be understood from a frustrated Lewis pair formation with a partial electron donation of the lone-pair on nitrogen together with competitive bonding to other species as revealed by Raman spectroscopy and DFT calculations. The bleached phase consists of methylammonium iodide crystals and an amorphous phase of PbI2( pyridine)(2). After spontaneous recrystallization the CH3NH3PbI3 thin films have remarkably improved photoluminescence, and solar cell performance increased from 9.5% for as-deposited films to more than 18% power conversion efficiency for recrystallized films in solar cells with planar geometry under AM1.5G illumination. Hysteresis was negligible and open-circuit potential was remarkably high, 1.15 V. The results show that complete recrystallization can be achieved with a simple room temperature pyridine vapor treatment of CH3NH3PbI3 films leading to high quality crystallinity films with drastically improved photovoltaic performance.
|
|
| 6. |
|
|
| 7. |
- Mirmohades, Mohammad, et al.
(författare)
-
Direct Observation of Key Catalytic Intermediates in a Photoinduced Proton Reduction Cycle with a Diiron Carbonyl Complex
- 2014
-
Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 136:50, s. 17366-17369
-
Tidskriftsartikel (refereegranskat)abstract
- The structure and reactivity of intermediatesin the photocatalytic cycle of a proton reductioncatalyst, [Fe2(bdt)(CO)6] (bdt = benzenedithiolate), wereinvestigated by time-resolved spectroscopy. The singlyreduced catalyst [Fe2(bdt)(CO)6]−, a key intermediate inphotocatalytic H2 formation, was generated by reactionwith one-electron reductants in laser flash-quench experimentsand could be observed spectroscopically on thenanoseconds to microseconds time scale. From UV/visand IR spectroscopy, [Fe2(bdt)(CO)6]− is readilydistinguished from the two-electron reduced catalyst[Fe2(bdt)(CO)6]2− that is obtained inevitably in theelectrochemical reduction of [Fe2(bdt)(CO)6]. For thedisproportionation rate constant of [Fe2(bdt)(CO)6]−, anupper limit on the order of 107 M−1 s−1 was estimated,which precludes a major role of [Fe2(bdt)(CO)6]2− inphotoinduced proton reduction cycles. Structurally [Fe2-(bdt)(CO)6]− is characterized by a rather asymmetricallydistorted geometry with one broken Fe−S bond and sixterminal CO ligands. Acids with pKa ≤ 12.7 protonate[Fe2(bdt)(CO)6]− with bimolecular rate constants of 4 ×106, 7 × 106, and 2 × 108 M−1 s−1 (trichloroacetic,trifluoroacetic, and toluenesulfonic acids, respectively).The resulting hydride complex [Fe2(bdt)(CO)6H] istherefore likely to be an intermediate in photocatalyticcycles. This intermediate resembles structurally andelectronically the parent complex [Fe2(bdt)(CO)6], withvery similar carbonyl stretching frequencies.
|
|
| 8. |
- Mirmohades, Mohammad, et al.
(författare)
-
Following [FeFe] Hydrogenase Active Site Intermediates by Time-Resolved Mid-IR Spectroscopy
- 2016
-
Ingår i: The Journal of Physical Chemistry Letters. - : American Chemical Society (ACS). - 1948-7185. ; 7:16, s. 3290-3293
-
Tidskriftsartikel (refereegranskat)abstract
- Time-resolved nanosecond mid-infrared spectroscopy is for the first time employed to study the [FeFe] hydrogenase from Chlamydomonas reinhardtii and to investigate relevant intermediates of the enzyme active site. An actinic 355 nm, 10 ns laser flash triggered photodissociation of a carbonyl group from the CO-inhibited state H-ox-CO to form the state H-ox, which is an intermediate of the catalytic proton reduction cycle. Time-resolved infrared spectroscopy allowed us to directly follow the subsequent rebinding of the carbonyl, re-forming H-ox-CO, and determine the reaction half-life to be t(1/2) approximate to 13 +/- 5 ms at room temperature. This gives direct information GO on the dynamics of CO inhibition of the enzyme.
|
|
| 9. |
- Mirmohades, Mohammad, 1986-
(författare)
-
Insight into Catalytic Intermediates Relevant for Water Splitting
- 2016
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Catalysis is an important part of chemistry. This is also reflected in the chemical industry where 85-90 % of all products are made catalytically. Also nature employs catalysts, i.e. enzymes, for its reactions.To improve on the already existing catalysts one can learn a lot from nature which often uses earth-abundant elements in the enzymes which have also been optimized and finely tuned for billions of years. To gain a deeper understanding of both enzymatic and artificial catalysis one needs to investigate the mechanism of the catalytic process. But for very efficient catalysts with turnover frequencies of several thousand per second this is not easy, since an investigation of the mechanism involves resolving intermediates in the catalytic cycle. The intermediates in these instances are short-lived corresponding to their turnover frequencies. A maximum turnover frequency of 1,000 s-1 e.g. means that each catalyst goes through the whole catalytic cycle in 1 ms. Therefore time-resolved techniques are necessary that have a faster detection speed than the turnover frequency of the catalyst.Flash photolysis is a spectroscopic technique with an instrument response function down to 10 ns. Coupling this technique with mid-infrared probing yields an excellent detection system for probing different redox and protonation states of carbonyl metal complexes. Since many catalysts as well as natural enzymes involved in water splitting are metal carbonyl complexes this is an ideal technique to monitor the intermediates of these catalysts.Chapter 3 covers the investigation of [FeFe] hydrogenases, enzymes that catalyze the reduction of protons to hydrogen in nature. Chapter 4 investigates the intermediates of biomimetic complexes, resembling the active site of natural [FeFe] hydrogenases. Chapter 5 covers the insights gained from investigating other catalysts which are also involved in water splitting and artificial photosynthesis.
|
|
| 10. |
- Singh, Wangkheimayum Marjit, et al.
(författare)
-
Voltammetric and spectroscopic characterization of early intermediates in the Co(II)-polypyridyl-catalyzed reduction of water
- 2013
-
Ingår i: Chemical Communications. - : Royal Society of Chemistry (RSC). - 1359-7345 .- 1364-548X. ; 49:77, s. 8638-8640
-
Tidskriftsartikel (refereegranskat)abstract
- Early intermediates of catalytic water reduction by a Co(II)-polypyridyl species have been characterized. Electrochemical detection of the Co(III)-hydride and time-resolved spectroscopic detection of the Co(I)-ligand intermediates provide an understanding of their reactivity in electrolytic or light-driven reduction of protons to hydrogen.
|
|
