| 1. |
- Abdellah, Mohamed, et al.
(författare)
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Competitive Hole Transfer from CdSe Quantum Dots to Thiol Ligands in CdSe-Cobaloxime Sensitized NiO Films Used as Photocathodes for H-2 Evolution
- 2017
-
Ingår i: ACS Energy Letters. - : American Chemical Society (ACS). - 2380-8195. ; 2:11, s. 2576-2580
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Tidskriftsartikel (refereegranskat)abstract
- Quantum dot (QD) sensitized NiO photocathodes rely on efficient photoinduced hole injection into the NiO valence band. A system of a mesoporous NiO film co-sensitized with CdSe QDs and a molecular proton reduction catalyst was studied. While successful electron transfer from the excited QDs to the catalyst is observed, most of the photogenerated holes are instead quenched very rapidly (ps) by hole trapping at the surface thiols of the capping agent used as linker molecules. We confirmed our conclusion by first using a thiol free capping agent and second varying the thiol concentration on the QD's surface. The later resulted in faster hole trapping as the thiol concentration increased. We suggest that this hole trapping by the linker limits the H-2 yield for this photocathode in a device.
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| 2. |
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| 3. |
- Abrahamsson, Maria, et al.
(författare)
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Microsecond (MLCT)-M-3 excited state lifetimes in bis-tridentate Ru(II)-complexes : significant reductions of non-radiative rate constants
- 2017
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Ingår i: Dalton Transactions. - : ROYAL SOC CHEMISTRY. - 1477-9226 .- 1477-9234. ; 46:39, s. 13314-13321
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we report the photophysical properties of a series of bis-tridentate Ru-II-complexes, based on the dqp-ligand (dqp = 2,6-di(quinolin-8-yl) pyridine), which display several microsecond long excited state lifetimes for triplet metal-to-ligand charge transfer ((MLCT)-M-3) at room temperature. Temperature dependence of the excited state lifetimes for [Ru(dqp)(2)](2+) and [Ru(dqp)(ttpy)](2+) (ttpy = 4'-tolyl-2,2': 6', 2 ''-terpyridine) is reported and radiative and non-radiative rate constants for the whole series are reported and discussed. We can confirm previous assumptions that the near-octahedricity of the bis-dqp complexes dramatically slows down activated decay at room temperature, as compared to most other and less long-lived bis-tridentate RuII-complexes, such as [Ru(tpy)(2)](2+) with tau = 0.25 ns at room temperature (tpy = 2,2': 6', 2 ''-terpyridine). Moreover, the direct non-radiative decay to the ground state is comparatively slow for similar to 700 nm room-temperature emission when considering the energy-gap law. Analysis of the 77 K emission spectra suggests that this effect is not primarily due to smaller excited state distortion than that for comparable complexes. Instead, an analysis of the photophysical parameters suggests a weaker singlet-triplet mixing in the MLCT state, which slows down both radiative and non-radiative decay.
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| 4. |
- Ahmed, Md Estak, et al.
(författare)
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A Bidirectional Bioinspired [FeFe]-Hydrogenase Model
- 2022
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 144:8, s. 3614-3625
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Tidskriftsartikel (refereegranskat)abstract
- With the price-competitiveness of solar and wind power, hydrogen technologies may be game changers for a cleaner, defossilized, and sustainable energy future. H-2 can indeed be produced in electrolyzers from water, stored for long periods, and converted back into power, on demand, in fuel cells. The feasibility of the latter process critically depends on the discovery of cheap and efficient catalysts able to replace platinum group metals at the anode and cathode of fuel cells. Bioinspiration can be key for designing such alternative catalysts. Here we show that a novel class of iron-based catalysts inspired from the active site of [FeFe]-hydrogenase behave as unprecedented bidirectional electrocatalysts for interconverting H-2 and protons efficiently under near-neutral aqueous conditions. Such bioinspired catalysts have been implemented at the anode of a functional membrane-less H-2/O-2 fuel cell device.
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| 5. |
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| 6. |
- Arkhypchuk, Anna I., et al.
(författare)
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Mechanistic Insights and Synthetic Explorations of the Photoredox-Catalyzed Activation of Halophosphines
- 2023
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Ingår i: Inorganic Chemistry. - : American Chemical Society (ACS). - 0020-1669 .- 1520-510X. ; 62:45, s. 18391-18398
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Tidskriftsartikel (refereegranskat)abstract
- The light-driven activation of halophosphines R2PX (R = alkyl- or aryl, X = Cl, Br) by an IrIII-based photocatalyst is described. It is shown that initially formed secondary phosphines R2PH react readily with the remaining R2PX in a parent–child reaction to form diphosphines R2P–PR2. Aryl-containing diphosphines can be further reduced to secondary phosphines RAr2PH under identical photoredox conditions. Dihalophosphines RPX2 are also activated by the photoredox protocol, giving rise to unusual 3-, 4-, and 5-membered cyclophosphines. Transient absorption studies show that the excited state of the Ir photocatalyst is reductively quenched by the DIPEA (N,N-di-iso-propylethylamine) electron donor. Electron transfer to R2PX is however unexpectedly slow and cannot compete with recombination with the oxidized donor DIPEA•+. As DIPEA is not a perfectly reversible donor, a small proportion of the total IrII population escapes recombination, providing the reductant for the observed transformations.
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| 7. |
- Aster, Alexander, et al.
(författare)
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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
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Ingår i: Chemical Science. - : Royal Society of Chemistry. - 2041-6520 .- 2041-6539. ; 10:21, s. 5582-5588
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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.
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| 8. |
- Axelsson, Martin, 1993-
(författare)
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Illuminating Benzothiadiazole : Mechanistic Insights into its Role in Fuel-Forming Reactions
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Development and understanding of catalytic reactions involved in fuel formation are crucial to be able to make the energy transition into a sustainable future. One intriguing type of catalyst for these types of reactions is organic material catalysts, which combine some of the tunable nature of molecular catalysts with the scalability and robust nature of material catalysts. The understanding of the catalytic mechanisms in these types of materials is still a work in progress. In the last decade D-A type polymers have gotten a lot of attention as potential photocatalysts for fuel-forming reactions but currently, the mechanisms in which these reactions take place are very limited.This thesis focuses on the molecular unit benzothiadiazole (BT) and its role in catalytic fuel-forming reactions across various molecules and polymers. In paper I: The hydrogen evolution reaction (HER) is investigated on the small molecule 2,1,3-benzothiadiazole-4,7dicarbonitrile (BT). The study reveals that BTDN serves as an electrocatalyst for the HER. Some catalytic intermediates were identified spectroscopically and a catalytic mechanism was proposed.In papers II and III: Polymeric nanoparticles (Pdots) based on the polymer poly(9,9- dioctylfluorene-alt-2,1,3-benzothiadiazole (PFBT) were investigated for photocatalytic fuel-forming reactions. First, the HER was explored and it emphasised the significance of proton binding to the BT unit as a catalytic intermediate. It also showed that changing to basic conditions can quench the HER and make place for CO2 reduction to CO and that PFBT Pdots exhibit good selectivity in catalyzing this reaction.Finally, in Paper IV, the binding and reduction of CO2 on the molecule BTDN were investigated. It was shown that BTDN can bind CO2 in multiple reduced states and reduce it to CO and oxalate in a third reduction, albeit with seemingly low efficiencies.
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| 9. |
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| 10. |
- Bagnall, Andrew J., et al.
(författare)
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Ultrafast Electron Transfer from CuInS2 Quantum Dots to a Molecular Catalyst for Hydrogen Production : Challenging Diffusion Limitations
- 2024
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Ingår i: ACS Catalysis. - 2155-5435. ; 14:6, s. 4186-4201
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Tidskriftsartikel (refereegranskat)abstract
- Systems integrating quantum dots with molecular catalysts are attracting ever more attention, primarily owing to their tunability and notable photocatalytic activity in the context of the hydrogen evolution reaction (HER) and CO2 reduction reaction (CO2RR). CuInS2 (CIS) quantum dots (QDs) are effective photoreductants, having relatively high-energy conduction bands, but their electronic structure and defect states often lead to poor performance, prompting many researchers to employ them with a core–shell structure. Molecular cobalt HER catalysts, on the other hand, often suffer from poor stability. Here, we have combined CIS QDs, surface-passivated with l-cysteine and iodide from a water-based synthesis, with two tetraazamacrocyclic cobalt complexes to realize systems which demonstrate high turnover numbers for the HER (up to >8000 per catalyst), using ascorbate as the sacrificial electron donor at pH = 4.5. Photoluminescence intensity and lifetime quenching data indicated a large degree of binding of the catalysts to the QDs, even with only ca. 1 μM each of QDs and catalysts, linked to an entirely static quenching mechanism. The data was fitted with a Poissonian distribution of catalyst molecules over the QDs, from which the concentration of QDs could be evaluated. No important difference in either quenching or photocatalysis was observed between catalysts with and without the carboxylate as a potential anchoring group. Femtosecond transient absorption spectroscopy confirmed ultrafast interfacial electron transfer from the QDs and the formation of the singly reduced catalyst (CoII state) for both complexes, with an average electron transfer rate constant of ≈ (10 ps)−1. These favorable results confirm that the core tetraazamacrocyclic cobalt complex is remarkably stable under photocatalytic conditions and that CIS QDs without inorganic shell structures for passivation can act as effective photosensitizers, while their smaller size makes them suitable for application in the sensitization of, inter alia, mesoporous electrodes.
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| 11. |
- Banin, U., et al.
(författare)
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Nanotechnology for catalysis and solar energy conversion
- 2021
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Ingår i: Nanotechnology. - : Institute of Physics Publishing (IOPP). - 0957-4484 .- 1361-6528. ; 32:4
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Tidskriftsartikel (refereegranskat)abstract
- This roadmap on Nanotechnology for Catalysis and Solar Energy Conversion focuses on the application of nanotechnology in addressing the current challenges of energy conversion: 'high efficiency, stability, safety, and the potential for low-cost/scalable manufacturing' to quote from the contributed article by Nathan Lewis. This roadmap focuses on solar-to-fuel conversion, solar water splitting, solar photovoltaics and bio-catalysis. It includes dye-sensitized solar cells (DSSCs), perovskite solar cells, and organic photovoltaics. Smart engineering of colloidal quantum materials and nanostructured electrodes will improve solar-to-fuel conversion efficiency, as described in the articles by Waiskopf and Banin and Meyer. Semiconductor nanoparticles will also improve solar energy conversion efficiency, as discussed by Boschloo et al in their article on DSSCs. Perovskite solar cells have advanced rapidly in recent years, including new ideas on 2D and 3D hybrid halide perovskites, as described by Spanopoulos et al 'Next generation' solar cells using multiple exciton generation (MEG) from hot carriers, described in the article by Nozik and Beard, could lead to remarkable improvement in photovoltaic efficiency by using quantization effects in semiconductor nanostructures (quantum dots, wires or wells). These challenges will not be met without simultaneous improvement in nanoscale characterization methods. Terahertz spectroscopy, discussed in the article by Milot et al is one example of a method that is overcoming the difficulties associated with nanoscale materials characterization by avoiding electrical contacts to nanoparticles, allowing characterization during device operation, and enabling characterization of a single nanoparticle. Besides experimental advances, computational science is also meeting the challenges of nanomaterials synthesis. The article by Kohlstedt and Schatz discusses the computational frameworks being used to predict structure-property relationships in materials and devices, including machine learning methods, with an emphasis on organic photovoltaics. The contribution by Megarity and Armstrong presents the 'electrochemical leaf' for improvements in electrochemistry and beyond. In addition, biohybrid approaches can take advantage of efficient and specific enzyme catalysts. These articles present the nanoscience and technology at the forefront of renewable energy development that will have significant benefits to society.
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| 12. |
- Bozal-Ginesta, Carlota, et al.
(författare)
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Self-Recovery of Photochemical H2 Evolution with a Molecular Diiron Catalyst Incorporated in a UiO-66 Metal-Organic Framework
- 2020
-
Ingår i: ChemPhotoChem. - : Wiley. - 2367-0932. ; 4:4, s. 287-290
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Tidskriftsartikel (refereegranskat)abstract
- Photochemical hydrogen evolution from a UiO‐66‐incorporated Fe2(dcbdt)(CO)6 catalyst in conjunction with a ruthenium photosensitizer and an ascorbate donor ceases after a period of irradiation, but is restored after a 60 min. resting period in the dark. Control experiments show that neither product inhibition nor pore clogging is responsible for this surprising behaviour, and intra‐crystal linker scrambling is proposed as a potential explanation.
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| 13. |
- Brnovic, Andjela, et al.
(författare)
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Mechanistic Insights into the Photocatalytic Hydrogen Production of Y5 and Y6 Nanoparticles
- 2023
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 127:26, s. 12631-12639
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Tidskriftsartikel (refereegranskat)abstract
- Utilization of solarenergy in organic semiconductorsrelies oncomplicated photophysical processes due to the strong electron-holeinteractions. To gain a better understanding of these processes andtheir effect on the photocatalytic performance of non-fullerene acceptors(NFAs) within nanoparticles (NPs), we compared the excited-state dynamicsand photocatalytic hydrogen production activity of two NFA-based NPs,Y5 and Y6. Our results show that under LED light irradiation, Y5 NPsexhibit 14 times better hydrogen production activity than Y6 NPs.The hydrogen production activity was also evaluated under Xenon lightirradiation (AM1.5G, 100 mW & BULL;cm(-2)) for Y5 NPs,yielding 410 mmol/g after 24 h. Time-resolved spectroscopy experimentsrevealed a longer triplet lifetime for Y5 compared to Y6 NPs, andthe lifetime was reduced upon addition of the electron donor ascorbate.This suggests the involvement of the triplet state in reductive quenchingand better hydrogen evolution reaction performance for Y5 NPs. Thegood agreement between fluorescence and triplet lifetimes observedfor Y5 NPs was attributed to reverse intersystem crossing, which repopulatesthe excited singlet state through thermally activated delayed fluorescence(TADF). The absence of TADF in Y6 NPs could limit its efficiency forhydrogen evolution reaction, in addition to the intrinsically shortertriplet lifetime and reduction potential difference, making it animportant factor to consider in Y series-based NPs.
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| 14. |
- Cellini, Andrea, 1991, et al.
(författare)
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Directed ultrafast conformational changes accompany electron transfer in a photolyase as resolved by serial crystallography.
- 2024
-
Ingår i: Nature chemistry. - : Springer Nature. - 1755-4349 .- 1755-4330.
-
Tidskriftsartikel (refereegranskat)abstract
- Charge-transfer reactions in proteins are important for life, such as in photolyases which repair DNA, but the role of structural dynamics remains unclear. Here, using femtosecond X-ray crystallography, we report the structural changes that take place while electrons transfer along a chain of four conserved tryptophans in the Drosophila melanogaster (6-4) photolyase. At femto- and picosecond delays, photoreduction of the flavin by the first tryptophan causes directed structural responses at a key asparagine, at a conserved salt bridge, and by rearrangements of nearby water molecules. We detect charge-induced structural changes close to the second tryptophan from 1 ps to 20 ps, identifying a nearby methionine as an active participant in the redox chain, and from 20 ps around the fourth tryptophan. The photolyase undergoes highly directed and carefully timed adaptations of its structure. This questions the validity of the linear solvent response approximation in Marcus theory and indicates that evolution has optimized fast protein fluctuations for optimal charge transfer.
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| 15. |
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| 16. |
- Cheng, Fangwen, et al.
(författare)
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Embedding biocatalysts in a redox polymer enhances the performance of dye-sensitized photocathodes in bias-free photoelectrochemical water splitting
- 2024
-
Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 15:1
-
Tidskriftsartikel (refereegranskat)abstract
- Dye-sensitized photoelectrodes consisting of photosensitizers and molecular catalysts with tunable structures and adjustable energy levels are attractive for low-cost and eco-friendly solar-assisted synthesis of energy rich products. Despite these advantages, dye-sensitized NiO photocathodes suffer from severe electron-hole recombination and facile molecule detachment, limiting photocurrent and stability in photoelectrochemical water-splitting devices. In this work, we develop an efficient and robust biohybrid dye-sensitized NiO photocathode, in which the intermolecular charge transfer is enhanced by a redox polymer. Owing to efficient assisted electron transfer from the dye to the catalyst, the biohybrid NiO photocathode showed a satisfactory photocurrent of 141±17 μA·cm−2 at neutral pH at 0 V versus reversible hydrogen electrode and a stable continuous output within 5 h. This photocathode is capable of driving overall water splitting in combination with a bismuth vanadate photoanode, showing distinguished solar-to-hydrogen efficiency among all reported water-splitting devices based on dye-sensitized photocathodes. These findings demonstrate the opportunity of building green biohybrid systems for artificial synthesis of solar fuels.
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| 17. |
- Cheng, Haoliang, et al.
(författare)
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Assessing the effect of surface states of mesoporous NiO films on charge transport and unveiling an unexpected light response phenomenon in tandem dye-sensitized solar cells
- 2022
-
Ingår i: Energy Advances. - : Royal Society of Chemistry. - 2753-1457. ; 1:5, s. 303-311
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, the role of NiO surface states is assessed in a tandem dye-sensitized solar cell (t-DSSC) consisting of a 4-(Bis-{4-[5-(2,2-dicyano-vinyl)-thiophene-2-yl]-phenyl}-amino)-benzoic acid (P1) dye-sensitized NiO photocathode, a VG1-C8 dye-sensitized TiO2 photoanode and the I−/I3− redox couple. The NiO surface states are proved to participate in the reduction of the I−/I3− electrolyte in the t-DSSCs. By adjusting the thickness of the TiO2 film, the charge transport processes of the t-DSSCs are significantly affected by the photocurrent and the NiO surface states, resulting in various photovoltaic properties. This work also proves that the NiO surface states together with energy transfer between the desorbed P1 dye from the NiO photocathode and the VG1-C8 dye from the TiO2 photoanode are responsible for the light response from both dyes observed in the IPCE spectra of the t-DSSCs.
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| 18. |
- Cotter, Laura F., et al.
(författare)
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Solvent and Temperature Effects on Photoinduced Proton-Coupled Electron Transfer in the Marcus Inverted Region
- 2021
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 125:35, s. 7670-7684
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Tidskriftsartikel (refereegranskat)abstract
- Concerted proton-coupled electron transfer (PCET) in the Marcus inverted region was recently demonstrated (Science 2019, 364, 471-475). Understanding the requirements for such reactivity is fundamentally important and holds promise as a design principle for solar energy conversion systems. Herein, we investigate the solvent polarity and temperature dependence of photoinduced proton-coupled charge separation (CS) and charge recombination (CR) in anthracene-phenol-pyridine triads: 1 (10-(4-hydroxy-3-(4-methylpyridin-2-yl)benzyl)anthracene-9-carbonitrile) and 2 (10-(4-hydroxy-3-(4-methoxypyridin-2-yl)benzyl)anthracene-9-carbonitrile). Both the CS and CR rate constants increased with increasing polarity in acetonitrile:n-butyronitrile mixtures. The kinetics were semi-quantitatively analyzed where changes in dielectric and refractive index, and thus consequently changes in driving force (-.G degrees) and reorganization energy (lambda), were accounted for. The results were further validated by fitting the temperature dependence, from 180 to 298 K, in n-butyronitrile. The analyses support previous computational work where transitions to proton vibrational excited states dominate the CR reaction with a distinct activation free energy (Delta G(CR)* similar to 140 meV). However, the solvent continuum model fails to accurately describe the changes in Delta G degrees and lambda with temperature via changes in dielectric constant and refractive index. Satisfactory modeling was obtained using the results of a molecular solvent model [J. Phys. Chem. B 1999, 103, 9130-9140], which predicts that lambda decreases with temperature, opposite to that of the continuum model. To further assess the solvent polarity control in the inverted region, the reactions were studied in toluene. Nonpolar solvents decrease both Delta G(CR)degrees and lambda, slowing CR into the nanosecond time regime for 2 in toluene at 298 K. This demonstrates how PCET in the inverted region may be controlled to potentially use proton-coupled CS states for efficient solar fuel production and photoredox catalysis.
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| 19. |
- D'Amario, Luca, et al.
(författare)
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Chemical and Physical Reduction of High Valence Ni States in Mesoporous NiO Film for Solar Cell Application
- 2017
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 9:39, s. 33470-33477
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Tidskriftsartikel (refereegranskat)abstract
- The most common material for dye-sensitized photocathodes is mesoporous NiO. We transformed the usual brownish NiO to be more transparent by reducing high valence Ni impurities. Two pretreatment methods have been used: chemical reduction by NaBH4 and thermal reduction by heating. The power conversion efficiency of the cell was increased by 33% through chemical treatment, and an increase in open-circuit voltage from 105 to 225 mV was obtained upon heat treatment. By optical spectroelectrochemistry, we could identify two species with characteristically different spectra assigned to Ni3+ and Ni4+. We suggest that the reduction of surface Ni3+ and Ni (4+) to Ni (2+) decreases the recombination reaction between holes on the NiO surface with the electrolyte. It also keeps the dye firmly on the surface, building a barrier for electrolyte recombination. This causes an increase in open-circuit photovoltage for the treated film.
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| 20. |
- D'Amario, Luca, 1986-, et al.
(författare)
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Unveiling hole trapping and surface dynamics of NiO nanoparticles
- 2018
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Ingår i: Chemical Science. - 2041-6520 .- 2041-6539. ; 9:1, s. 223-230
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Tidskriftsartikel (refereegranskat)abstract
- The research effort in mesoporous p-type semiconductors is increasing due to their potential application in photoelectrochemical energy conversion devices. In this paper an electron-hole pair is created by band-gap excitation of NiO nanoparticles and the dynamics of the electron and the hole is followed until their recombination. By spectroscopic characterization it was found that surface Ni3+ states work as traps for both electrons and holes. The trapped electron was assigned to a N2+ state and the trapped hole to a Ni4+ state. The recombination kinetics of these traps was studied and related with the concept of hole relaxation suggested before.The timescale of the hole relaxation was foundto be in the order of tens of ns. Finally the spectrosc opic evidence of this relaxation is presented in a sensitized film.
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| 21. |
- Dongare, Prateek, et al.
(författare)
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Analysis of Hydrogen-Bonding Effects on Excited-State Proton-Coupled Electron Transfer from a Series of Phenols to a Re(I) Polypyridyl Complex
- 2017
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Ingår i: The Journal of Physical Chemistry C. - : AMER CHEMICAL SOC. - 1932-7447 .- 1932-7455. ; 121:23, s. 12569-12576
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Tidskriftsartikel (refereegranskat)abstract
- In the present study of proton-coupled electron transfer (PCET) reactions, the excited-state of a fac-[(CO)(3)Re-I(bpy)(4,4'-bpy)](+) (bpy = 2,2'-bipyridine and 4,4'-bpy = 4,4'-bipyridine) complex was reductively quenched by a series of phenols. A variation of substituents on the phenols substantially alters their pK(a) and E degrees values and provides an opportunity to study photoinduced PCET as a function of their redox properties. Analyses of absorption spectral changes indicate that the phenols form a weak hydrogen bond with the pyridinic nitrogen of the 4,4'-bpy ligand in the ground-state, and ground-state association, constant (K-A) values were determined. This H-bonded adduct quenches the excited Re complex by PCET from the phenol, to form the reduced and,protonated Re complex. The KA values-obtained aid quantitative evaluation of the rate constant for the PCET reaction in the H-bonded, adduct. Thus, photophysical studies and Mechanistic analysis indicate that the reaction occurs via a concerted mechanistic pathway, for the unsubstituted phenol and phenols with electron-withdrawing subtituents. Furthermore; the magnitude of the quenching varies systematically with the proton-coupled potentials of the phenols and not their hydrogen-bonding strength (as reflected in K-A). This study is one of the first detailed analyses of intermolecular H-bonding between a self-assembling metal complex and a series of substituted phenols in an effort to study their relationship with the kinetic parameters in a photoinduced CPET reaction.
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| 22. |
- Dürr, Robin N., et al.
(författare)
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From NiMoO4 to γ-NiOOH : Detecting the Active Catalyst Phase by Time Resolved in Situ and Operando Raman Spectroscopy
- 2021
-
Ingår i: ACS Nano. - : American Chemical Society (ACS). - 1936-0851 .- 1936-086X. ; 15:8, s. 13504-13515
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Tidskriftsartikel (refereegranskat)abstract
- Water electrolysis powered by renewable energies is a promising technology to produce sustainable fossil free fuels. The development and evaluation of effective catalysts are here imperative; however, due to the inclusion of elements with different redox properties and reactivity, these materials undergo dynamical changes and phase transformations during the reaction conditions. NiMoO4 is currently investigated among other metal oxides as a promising noble metal free catalyst for the oxygen evolution reaction. Here we show that at applied bias, NiMoO4·H2O transforms into γ-NiOOH. Time resolved operando Raman spectroscopy is utilized to follow the potential dependent phase transformation and is collaborated with elemental analysis of the electrolyte, confirming that molybdenum leaches out from the as-synthesized NiMoO4·H2O. Molybdenum leaching increases the surface coverage of exposed nickel sites, and this in combination with the formation of γ-NiOOH enlarges the amount of active sites of the catalyst, leading to high current densities. Additionally, we discovered different NiMoO4 nanostructures, nanoflowers, and nanorods, for which the relative ratio can be influenced by the heating ramp during the synthesis. With selective molybdenum etching we were able to assign the varying X-ray diffraction (XRD) pattern as well as Raman vibrations unambiguously to the two nanostructures, which were revealed to exhibit different stabilities in alkaline media by time-resolved in situ and operando Raman spectroscopy. We advocate that a similar approach can beneficially be applied to many other catalysts, unveiling their structural integrity, characterize the dynamic surface reformulation, and resolve any ambiguities in interpretations of the active catalyst phase.
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| 23. |
- Eliasson, Nora, et al.
(författare)
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Ultrafast Dynamics in Cu-Deficient CuInS2 Quantum Dots : SubBandgap Transitions and Self-Assembled Molecular Catalysts
- 2021
-
Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:27, s. 14751-14764
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Tidskriftsartikel (refereegranskat)abstract
- The photophysical properties of Cu-deficient Cu01.2In1Sx quantum dots synthesized through a facile aqueous-based procedure have been investigated. Transient absorption experiments were carried out probing in the UV-vis, near-IR, and mid-IR regions, with the aim to (i) study the photophysical properties of the quantum dots and (ii) monitor kinetics of electron transfer to a molecular catalyst. When pumping subbandgap transitions, negative (bleach) signals were observed that were spectrally and kinetically distinct from those observed with bandgap pump wavelengths. Herein, these distinct contributions are suggested to result from the overlapping bleaching of state filling electrons and trapped holes. Such an interpretation highlights the importance of considering the hole-contributions to the bleach for the proper determination of carrier kinetics in similar systems. A model complex of the [Fe-2]-hydrogenase active site was introduced to explore the potential of the quantum dots as photosensitizers for molecular catalysts. The quantum dot photoluminescence was quenched upon catalyst addition, and direct evidence of the singly reduced catalyst was found by transient absorption in the UV-vis and mid-IR. The catalyst accepted reducing equivalents on a subpicosecond time scale upon photoexcitation of the quantum dots, despite no covalent linking chemistry being applied. This implies that charge transfer is not limited by diffusion rates, thus confirming the presence of spontaneous quantum dot and catalyst self-assembly.
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| 24. |
- Farré, Yoann, et al.
(författare)
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A Comparative Investigation of the Role of the Anchoring Group on Perylene Monoimide Dyes in NiO-Based Dye-Sensitized Solar Cells
- 2020
-
Ingår i: ChemSusChem. - : Wiley. - 1864-5631 .- 1864-564X. ; 13:7, s. 1844-1855
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Tidskriftsartikel (refereegranskat)abstract
- The anchoring group of a sensitizer may strongly affect the overall properties and stability of the resulting dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthetic solar cells (DSPECs). The properties of seven perylene monoimide (PMI) dyes have been comprehensively studied for their immobilization on nanocrystalline NiO film. The PMI dyes differ only by the nature of the anchoring group, which are: carboxylic acid (PMI-CO2H), phosphonic acid (PMI-PO3H2), acetyl acetone (PMI-acac), pyridine (PMI-Py), aniline (PMI-NH2), hydroxyquinoline (PMI-HQ), and dipicolinic acid (PMI-DPA). The dyes are investigated by cyclic voltammetry and spectroelectrochemistry and modeled by TD-DFT quantum chemical calculations. The mode of binding of these anchoring groups is investigated by infrared spectroscopy and the stability of the binding to NiO surface is studied by desorption experiments in acidic and basic media. The phosphonic acid group is found to offer the strongest binding to the NiO surface in terms of stability and dye loading. Finally, a photophysical study by ultrafast transient absorption spectroscopy shows that all dyes inject a hole in NiO with rate constants on a subpicosecond timescale and display similar charge recombination kinetics. The photovoltaic properties of the dyes show that PMI-HQ and PMI-acac give the highest photovoltaic performances, owing to a lower degree of aggregation on the surface.
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| 25. |
- Favereau, Ludovic, et al.
(författare)
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Tris-bipyridine based dinuclear ruthenium(II)--osmium(III) complex dyads grafted onto TiO2 nanoparticles for mimicking the artificial photosynthetic Z-scheme
- 2017
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Ingår i: Physical Chemistry, Chemical Physics - PCCP. - : Royal Society of Chemistry. - 1463-9076 .- 1463-9084. ; 19:6, s. 4778-4786
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Tidskriftsartikel (refereegranskat)abstract
- The Z-Scheme function within molecular systems has been rarely reported for solar energy conversion although it offers the possibility to achieve higher efficiency than single photon absorber photosystems due to the use of a wider range of visible light. In this study, we synthesized and investigated the electrochemical and spectroscopic properties of two new dyads based on ruthenium and osmium tris-bipyridine complexes covalently linked via a butane bridge to explore their ability to realize the Z-scheme function once immobilized on TiO2. These dyads can be grafted onto a nanocrystalline TiO2 film via the osmium complex bearing two dicarboxylic acid bipyridine ligands, while the ruthenium complex contains either two unsubstituted bipyridine ancillary ligands (RuH-Os) or two (4,4'-bis-trifluoro-methyl-bipyridine) ancillary ligands (RuCF3-Os). Transient absorption spectroscopy studies of the Ru(II)-Os(III) dyads with femtosecond and nanosecond lasers were conducted both in solution and on TiO2. For both conditions, the photophysical studies revealed that the MLCT excited state of the ruthenium complex is strongly quenched and predominantly decays by energy transfer to the LMCT of the adjacent Os(III) complex, in spite of the high driving force for electron transfer. This unexpected result, which is in sharp contrast to previously reported Ru(II)-Os(III) dyads, precluded us to achieve the expected Z-scheme function. However, the above results may be a guide for designing new artificial molecular systems reproducing the complex function of a Z-scheme with molecular systems grafted onto a TiO2 mesoporous film.
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