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- Segev, Gideon, et al.
(author)
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The 2022 solar fuels roadmap
- 2022
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In: Journal of Physics D. - : IOP Publishing. - 0022-3727 .- 1361-6463. ; 55:32
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Journal article (peer-reviewed)abstract
- Renewable fuel generation is essential for a low carbon footprint economy. Thus, over the last five decades, a significant effort has been dedicated towards increasing the performance of solar fuels generating devices. Specifically, the solar to hydrogen efficiency of photoelectrochemical cells has progressed steadily towards its fundamental limit, and the faradaic efficiency towards valuable products in CO2 reduction systems has increased dramatically. However, there are still numerous scientific and engineering challenges that must be overcame in order to turn solar fuels into a viable technology. At the electrode and device level, the conversion efficiency, stability and products selectivity must be increased significantly. Meanwhile, these performance metrics must be maintained when scaling up devices and systems while maintaining an acceptable cost and carbon footprint. This roadmap surveys different aspects of this endeavor: system benchmarking, device scaling, various approaches for photoelectrodes design, materials discovery, and catalysis. Each of the sections in the roadmap focuses on a single topic, discussing the state of the art, the key challenges and advancements required to meet them. The roadmap can be used as a guide for researchers and funding agencies highlighting the most pressing needs of the field.
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| 2. |
- Bowman, Lawrence E., et al.
(author)
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A single photon timing instrument that covers a broad temporal range in the reversed timing configuration
- 1993
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In: Review of Scientific Instruments. - : AIP Publishing. - 0034-6748 .- 1089-7623. ; 64:2, s. 338-341
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Journal article (peer-reviewed)abstract
- A versatile single-photon timing instrument based on the reversed timing configuration has been constructed. Unlike similar instruments, the apparatus described here is capable of recording a broad range of excited-state decay times owing to a switched fiber optic delay. This allows the user to readily collect time-resolved luminescence data over a variable time window in the reversed-timing configuration. With proper adjustment of the appropriate components, one can acquire a luminescence decay over a variable time range from less than 1 ns to nearly 1 μs. The full width at half-maximum of the instrument response function is 42 ps. The utility of a switched fiber optic delay is discussed and the device's construction is described.
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| 5. |
- Irebo, Tania, 1980-, et al.
(author)
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Proton-coupled electron transfer of tyrosine oxidation : buffer dependence and parallel mechanisms
- 2007
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 129:50, s. 15462-15464
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Journal article (peer-reviewed)abstract
- The proton-coupled electron transfer (PCET) from tyrosine covalently linked to a metal complex has been studied. The reaction was induced by laser flash excitation of the metal complex, and PCET was bidirectional, with electron transfer to the excited or flash-quenched oxidized metal complex and proton transfer to water or added buffers in the solution. We found a competition between three different PCET mechanisms: (1) A concerted PCET with water as the proton acceptor, which indeed shows a pH-dependence as earlier reported (Sjödin, M.; Styring, S.; Åkermark, B.; Sun, L.; Hammarström, L. J. Am. Chem. Soc. 2000, 122, 3932); (2) a stepwise electron transfer-proton transfer (ETPT) that is pH-independent; (3) a buffer-assisted concerted PCET. The relative importance of reaction 2 increases with oxidant strength, while that of reaction 1 increases with pH. At higher buffer concentrations reaction 3 becomes important, and the rate follows the expected first-order dependence on the concentration of the buffer base. Most importantly, the pH-dependence of reaction 1, with a slope of 0.4-0.5 in a plot of log k vs pH, is independent of buffer and cannot be explained by reaction schemes with simple first-order dependencies on [OH-], [H3O+], or buffer species.
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| 6. |
- McAlpin, J. Gregory, et al.
(author)
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Electronic Structure Description of a [Co(III)(3)Co(IV)O-4] Cluster : A Model for the Paramagnetic Intermediate in Cobalt-Catalyzed Water Oxidation
- 2011
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 0002-7863 .- 1520-5126. ; 133:39, s. 15444-15452
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Journal article (peer-reviewed)abstract
- Multifrequency electron paramagnetic resonace (EPR) spectroscopy and electronic structure calculations were performed on [Co4O4(C5H5N)(4)(CH3CO2)(4)](+) (1(+)), a cobalt tetramer with total electron spin S = 1/2 and formal cobalt oxidation states III, III, III, and IV. The cuboidal arrangement of its cobalt and oxygen atoms is similar to that of proposed structures for the molecular cobaltate clusters of the cobalt-phosphate (Co-Pi) water-oxidizing catalyst. The Davies electron-nuclear double resonance (ENDOR) spectrum is well-modeled using a single class of hyperfine-coupled Co-59 nuclei with a modestly strong interaction (principal elements of the hyperfine tensor are equal to [-20(+/- 2), 77(+/- 1), -5(+/- 15)] MHz). Mims H-1 ENDOR spectra of 1(+) with selectively deuterated pyridine ligands confirm that the amount of unpaired spin on the cobalt-bonding partner is significantly reduced from unity. Multifrequency N-14 ESEEM spectra (acquired at 9.5 and 34.0 GHz) indicate that four nearly equivalent nitrogen nuclei are coupled to the electron spin. Cumulatively, our EPR spectroscopic findings indicate that the unpaired spin is delocalized almost equally across the eight core atoms, a finding corroborated by results from DFT calculations. Each octahedrally coordinated cobalt ion is forced into a low-spin electron configuration by the anionic oxo and carboxylato ligands, and a fractional electron hole is localized on each metal center in a Co 3d(xz,yz)-based molecular orbital for this essentially [Co4+3.125O4] system. Comparing the EPR spectrum of 1(+) with that of the catalyst film allows us to draw conclusions about the electronic structure of this water-oxidation catalyst.
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| 7. |
- Sjödin, Martin, 1974-
(author)
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Regulation of Proton Coupled Electron Transfer from Amino Acids in Artificial Model Systems: A Mechanistic Study
- 2004
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Doctoral thesis (other academic/artistic)abstract
- Amino acid radicals are key redox intermediates in several natural enzymes including Cytochrome c peroxidase, DNA photolyase, ribonucletide reductase, cytochrome c oxidase and photosystem II. Electron transfer from amino acids is often coupled to deprotonation and this thesis concerns the coupling of electron transfer from tyrosine and tryptophan to trisbipyridineruthenium(III) with deprotonation in model complexes. Specifically the mechanisms for these proton coupled electron transfer reactions have been studied and the controlling parameters have been identified, the possible mechanisms being stepwise electron transfer followed by deprotonation and deprotonation followed by electron transfer or concerted electron transfer/deprotonation.Proton coupled electron transfer reactions have been studied using nano-second flash photolysis in water solution and the effect of pH, temperature, reaction driving force, deuteration and nature of the amino acid has been determined. I have shown that the rate constant for the concerted reaction depends intrinsically on the mixing entropy of the released proton and that the pH-dependence can be used as an experimental tool for mechanistic discrimination. Moreover I have shown that the concerted reaction inherently has a high reorganisation energy due to the coupling of the electron motion with deprotonation. Hydrogen bonding to the transferring proton however significantly reduces this reorganisation energy. The concerted reaction also has a relatively high driving force counteracting the high reorganisation energy in the competition between the concerted reaction and the stepwise electron transfer first reaction. The relative importance of the high reorganisation energy and the high driving force for the concerted reaction determines the mechanistic outcome of the reaction, the stepwise reaction being favoured by high over-all driving forces and the concerted reaction by high pH.By comparing my results from model complexes with tyrosineZ oxidation in photosystem II, I give strong evidence for a concerted electron transfer/deprotonation mechanism.
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