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Wang, V.-C. C., Esmieu, C., Redman, H. J., Berggren, G. & Hammarström, L. (2020). The reactivity of molecular oxygen and reactive oxygen species with [FeFe] hydrogenase biomimetics: reversibility and the role of the second coordination sphere. Dalton Transactions, 49(3), 858-865
Open this publication in new window or tab >>The reactivity of molecular oxygen and reactive oxygen species with [FeFe] hydrogenase biomimetics: reversibility and the role of the second coordination sphere
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2020 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 49, no 3, p. 858-865Article in journal (Refereed) Published
Abstract [en]

The development of oxygen-tolerant H-2-evolving catalysts plays a vital role for a future H-2 economy. For example, the [FeFe] hydrogenase enzymes are excellent catalyst for H-2 evolution but rapidly become inactivated in the presence of O-2. The mechanistic details of the enzyme's inactivation by molecular oxygen still remain unclear. Here, two H-2-evolving diiron complexes [Fe-2(mu-SCH2NHCH2S)(CO)(6)] (1(adt)) and [Fe-2(mu-SCH2CH2CH2S)(CO)(6)] (2(pdt)), inspired by the active site of [FeFe] hydrogenase, were investigated for their reactivity with molecular oxygen and reactive oxygen species. A one-electron reduced and oxygenated 1(adt) species was identified and characterized spectroscopically, which can be directly generated by reacting with molecular oxygen and chemical reductants at room temperature but it is unstable and gradually decomposes. Interestingly, the whole process is reversible and the addition of protons can facilitate the deoxygenation process and prevent further degradation at room temperature. This new identification of intermediate species serves as a model for studying the reversible inactivation and degradation of oxygen-sensitive [FeFe] hydrogenases by O-2, and provides chemical precedence for such processes. In comparison, the complex lacking the nitrogen bridgehead, 2(pdt), exhibits reduced reactivity towards O-2 in the presence of reductants, highlighting that the importance of the second coordination sphere on modulating the oxygenation processes. These results provide new directions to design molecular electrocatalysts for proton reduction operated at ambient conditions and the re-engineering of [FeFe] hydrogenases for improving oxygen tolerance.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2020
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-406172 (URN)10.1039/c9dt04618f (DOI)000509360800031 ()31854399 (PubMedID)
Funder
Swedish Research Council, 621-2014-5670EU, European Research Council, 714102
Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
Materna, K. L., Lalaoui, N., Laureanti, J. A., Walsh, A. P., Pettersson-Rimgard, B., Lomoth, R., . . . Hammarström, L. (2020). Using Surface Amide Couplings to Assemble Photocathodes for Solar Fuel Production Applications. ACS Applied Materials and Interfaces, 12(4), 4501-4509
Open this publication in new window or tab >>Using Surface Amide Couplings to Assemble Photocathodes for Solar Fuel Production Applications
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2020 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 12, no 4, p. 4501-4509Article in journal (Refereed) Published
Abstract [en]

A facile surface amide-coupling method was examined to attach dye and catalyst molecules to silatrane-decorated NiO electrodes. Using this method, electrodes with a push-pull dye were assembled and characterized by photoelectrochemistry and transient absorption spectroscopy. The dye-sensitized electrodes exhibited hole injection into NiO and good photoelectrochemical stability in water, highlighting the stability of the silatrane anchoring group and the amide linkage. The amide-coupling protocol was further applied to electrodes that contain a molecular proton reduction catalyst for use in photocathode architectures. Evidence for catalyst reduction was observed during photoelectrochemical measurements and via photocathodes.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
Keywords
solar fuels, photocathode, nickel oxide, silatrane, amide coupling
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-406495 (URN)10.1021/acsami.9b19003 (DOI)000510532000032 ()31872996 (PubMedID)
Funder
Swedish Energy Agency, 11674-8
Available from: 2020-03-11 Created: 2020-03-11 Last updated: 2020-03-11Bibliographically approved
Huang, J., Xu, B., Tian, L., Pati, P. B., Etman, A. S., Sun, J., . . . Tian, H. (2019). A heavy metal-free CuInS2 quantum dot sensitized NiO photocathode with a Re molecular catalyst for photoelectrochemical CO2 reduction. Chemical Communications, 55(55), 7918-7921
Open this publication in new window or tab >>A heavy metal-free CuInS2 quantum dot sensitized NiO photocathode with a Re molecular catalyst for photoelectrochemical CO2 reduction
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2019 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 55, no 55, p. 7918-7921Article in journal (Refereed) Published
Abstract [en]

Heavy metal-free CuInS2 quantum dots (QDs) were employed as a photosensitizer on a NiO photocathode to drive an immobilized molecular Re catalyst for photoelectrochemical CO2 reduction for the first time. A photocurrent of 25 mu A cm(-2) at -0.87 V vs. NHE was obtained, providing a faradaic efficiency of 32% for CO production.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-390783 (URN)10.1039/c9cc04222a (DOI)000474306200003 ()31215919 (PubMedID)
Funder
Swedish Energy Agency, 11674-8Göran Gustafsson Foundation for Research in Natural Sciences and MedicineStiftelsen Olle Engkvist Byggmästare
Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Parada, G. A., Goldsmith, Z. K., Kolmar, S., Pettersson-Rimgard, B., Mercado, B. Q., Hammarström, L., . . . Mayer, J. M. (2019). Concerted proton-electron transfer reactions in the Marcus inverted region. Science, 364(6439), 471-475
Open this publication in new window or tab >>Concerted proton-electron transfer reactions in the Marcus inverted region
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2019 (English)In: Science, ISSN 0036-8075, E-ISSN 1095-9203, Vol. 364, no 6439, p. 471-475Article in journal (Refereed) Published
Abstract [en]

Electron transfer reactions slow down when they become very thermodynamically favorable, a counterintuitive interplay of kinetics and thermodynamics termed the inverted region in Marcus theory. Here we report inverted region behavior for proton-coupled electron transfer (PCET). Photochemical studies of anthracene-phenol-pyridine triads give rate constants for PCET charge recombination that are slower for the more thermodynamically favorable reactions. Photoexcitation forms an anthracene excited state that undergoes PCET to create a charge-separated state. The rate constants for return charge recombination show an inverted dependence on the driving force upon changing pyridine substituents and the solvent. Calculations using vibronically nonadiabatic PCET theory yield rate constants for simultaneous tunneling of the electron and proton that account for the results.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-383503 (URN)10.1126/science.aaw4675 (DOI)000466809600031 ()30975771 (PubMedID)
Funder
Swedish Research Council, 2016-04271
Available from: 2019-05-17 Created: 2019-05-17 Last updated: 2019-05-17Bibliographically approved
Wang, S., Pullen, S., Weippert, V., Liu, T., Ott, S., Lomoth, R. & Hammarström, L. (2019). Direct Spectroscopic Detection of Key Intermediates and Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst. Chemistry - A European Journal, 25(47), 11135-11140
Open this publication in new window or tab >>Direct Spectroscopic Detection of Key Intermediates and Turnover Process in Catalytic H2 Formation by a Biomimetic Diiron Catalyst
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2019 (English)In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 25, no 47, p. 11135-11140Article in journal (Refereed) Published
Abstract [en]

[FeFe(Cl-2-bdt)(CO)(6)] (1; Cl-2-bdt=3,6-dichlorobenzene-1,2-dithiolate), inspired by the active site of FeFe-hydrogenase, shows a chemically reversible 2 e(-) reduction at -1.20 V versus the ferrocene/ferrocenium couple. The rigid and aromatic bdt bridging ligand lowers the reduction potential and stabilizes the reduced forms, compared with analogous complexes with aliphatic dithiolates; thus allowing details of the catalytic process to be characterized. Herein, time-resolved IR spectroscopy is used to provide kinetic and structural information on key catalytic intermediates. This includes the doubly reduced, protonated complex 1H(-), which has not been previously identified experimentally. In addition, the first direct spectroscopic observation of the turnover process for a molecular H-2 evolving catalyst is reported, allowing for straightforward determination of the turnover frequency.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-380278 (URN)10.1002/chem.201902100 (DOI)000479841700001 ()31210385 (PubMedID)
Funder
Swedish Research Council, 2016-04271Stiftelsen Olle Engkvist Byggmästare, 2016/3
Available from: 2019-03-26 Created: 2019-03-26 Last updated: 2019-10-31Bibliographically approved
Liu, T., Tyburski, R., Wang, S., Fernandez-Teran, R., Ott, S. & Hammarström, L. (2019). Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics. Journal of the American Chemical Society, 141(43), 17245-17259
Open this publication in new window or tab >>Elucidating Proton-Coupled Electron Transfer Mechanisms of Metal Hydrides with Free Energy- and Pressure-Dependent Kinetics
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2019 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 141, no 43, p. 17245-17259Article in journal (Refereed) Published
Abstract [en]

Proton-coupled electron transfer (PCET) was studied in a series of tungsten hydride complexes with pendant pyridyl arms ([(PyCH2Cp)WH(CO)(3)], PyCH2Cp = pyridyl methyl cyclopentadienyl), triggered by laser flash-generated Ru-III-tris-bipyridine oxidants, in acetonitrile solution. The free energy dependence of the rate constant and the kinetic isotope effects (KIEs) showed that the PCET mechanism could be switched between concerted and the two stepwise PCET mechanisms (electron-first or proton-first) in a predictable fashion. Straightforward and general guidelines for how the relative rates of the different mechanisms depend on oxidant and base are presented. The rate of the concerted reaction should depend symmetrically on changes in oxidant and base strength, that is on the overall Delta G(PCET)(0), and we argue that an "asynchronous" behavior would not be consistent with a model where the electron and proton tunnel from a common transition state. The observed rate constants and KIEs were examined as a function of hydrostatic pressure (1-2000 bar) and were found to exhibit qualitatively different dependence on pressure for different PCET mechanisms. This is discussed in terms of different volume profiles of the PCET mechanisms as well as enhanced proton tunneling for the concerted mechanism. The results allowed for assignment of the main mechanism operating in the different cases, which is one of the critical questions in PCET research. They also show how the rate of a PCET reaction will be affected very differently by changes of oxidant and base strength, depending on which mechanism dominates. This is of fundamental interest as well as of practical importance for rational design of, for example, catalysts for fuel cells and solar fuel formation, which operate in steps of PCET reactions. The mechanistic richness shown by this system illustrates that the specific mechanism is not intrinsic to a specific synthetic catalyst or enzyme active site but depends on the reaction conditions.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-397587 (URN)10.1021/jacs.9b08189 (DOI)000493866300030 ()31587555 (PubMedID)
Funder
Swedish Research Council, 2016-04271Stiftelsen Olle Engkvist Byggmästare, 2016/3
Available from: 2019-11-25 Created: 2019-11-25 Last updated: 2019-11-25Bibliographically approved
Ma, D., Kuno, M., Minteer, S., Hammarström, L. & Kamat, P. V. (2019). Energy Selects 2D Hybrids, Bioinspired Catalysts, and Lead-Free Perovskites. ACS ENERGY LETTERS, 4(9), 2351-2352
Open this publication in new window or tab >>Energy Selects 2D Hybrids, Bioinspired Catalysts, and Lead-Free Perovskites
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2019 (English)In: ACS ENERGY LETTERS, ISSN 2380-8195, Vol. 4, no 9, p. 2351-2352Article in journal, Editorial material (Other academic) Published
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-395631 (URN)10.1021/acsenergylett.9b01883 (DOI)000486361500042 ()
Available from: 2019-10-23 Created: 2019-10-23 Last updated: 2019-10-23Bibliographically approved
Queyriaux, N., Swords, W. B., Agarwata, H., Johnson, B. A., Ott, S. & Hammarström, L. (2019). Mechanistic insights on the non-innocent role of electron donors: reversible photocapture of CO2 by Ru-II-polypyridyl complexes. Dalton Transactions, 48(45), 16894-16898
Open this publication in new window or tab >>Mechanistic insights on the non-innocent role of electron donors: reversible photocapture of CO2 by Ru-II-polypyridyl complexes
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2019 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 45, p. 16894-16898Article in journal (Refereed) Published
Abstract [en]

The ability of [Ru-II((t)Butpy)(dmbpy)(MeCN)](2+) (1-MeCN) to capture CO2, with the assistance of triethanolamine (TEOA), has been assessed under photocatalytically-relevant conditions. The photolability of 1-MeCN has proven essential to generate a series of intermediates which only differ by the nature of their monodentate ligand. In DMF, ligand photoexchange of 1-MeCN to give [Ru-II((t)Butpy)(dmbpy)(DMF)](2+) (1-DMF) proceeds smoothly with a quantum yield of 0.011. However, in the presence of TEOA, this process was disrupted, leading to the formation of a mixture of 1-DMF and [Ru-II((t)Butpy)(dmbpy)(TEOA)](+) (1-TEOA). An equilibrium constant of 3 was determined. Interestingly, 1-TEOA demonstrated an ability to reversibly catch and release CO2 making it a potentially crucial intermediate towards CO2 reduction.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2019
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-400006 (URN)10.1039/c9dt03461g (DOI)000498690100006 ()31642825 (PubMedID)
Funder
Swedish Energy Agency, 11674-8Stiftelsen Olle Engkvist Byggmästare, 2016/3NordForsk
Available from: 2019-12-19 Created: 2019-12-19 Last updated: 2019-12-19Bibliographically approved
Aster, A., Wang, S., Mirmohades, M., Esmieu, C., Berggren, G., Hammarström, L. & Lomoth, R. (2019). Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes. Chemical Science, 10(21), 5582-5588
Open this publication in new window or tab >>Metal vs. ligand protonation and the alleged proton-shuttling role of the azadithiolate ligand in catalytic H-2 formation with FeFe hydrogenase model complexes
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2019 (English)In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 10, no 21, p. 5582-5588Article in journal (Refereed) Published
Abstract [en]

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.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-390686 (URN)10.1039/c9sc00876d (DOI)000474412700015 ()31293742 (PubMedID)
Funder
Swedish Research Council, 621-2014-5670Swedish Research Council, 2016-04271Swedish Research Council Formas, 213-2014-880
Available from: 2019-08-16 Created: 2019-08-16 Last updated: 2019-08-16Bibliographically approved
Liu, T., Guo, M., Orthaber, A., Lomoth, R., Lundberg, M., Ott, S. & Hammarström, L. (2018). Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions. Nature Chemistry, 10(8), 881-887
Open this publication in new window or tab >>Accelerating proton-coupled electron transfer of metal hydrides in catalyst model reactions
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2018 (English)In: Nature Chemistry, ISSN 1755-4330, E-ISSN 1755-4349, Vol. 10, no 8, p. 881-887Article in journal (Refereed) Published
Abstract [en]

Metal hydrides are key intermediates in catalytic proton reduction and dihydrogen oxidation. There is currently much interest in appending proton relays near the metal centre to accelerate catalysis by proton-coupled electron transfer (PCET). However, the elementary PCET steps and the role of the proton relays are still poorly understood, and direct kinetic studies of these processes are scarce. Here, we report a series of tungsten hydride complexes as proxy catalysts, with covalently attached pyridyl groups as proton acceptors. The rate of their PCET reaction with external oxidants is increased by several orders of magnitude compared to that of the analogous systems with external pyridine on account of facilitated proton transfer. Moreover, the mechanism of the PCET reaction is altered by the appended bases. A unique feature is that the reaction can be tuned to follow three distinct PCET mechanisms-electron-first, proton-first or a concerted reaction-with very different sensitivities to oxidant and base strength. Such knowledge is crucial for rational improvements of solar fuel catalysts.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-357209 (URN)10.1038/s41557-018-0076-x (DOI)000439420400015 ()30013192 (PubMedID)
Funder
Swedish Research Council, 2016-04271Knut and Alice Wallenberg Foundation, 2011.0067
Available from: 2018-08-13 Created: 2018-08-13 Last updated: 2019-01-04Bibliographically approved
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