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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: 2018-09-27Bibliographically approved
Johnson, B. A., Bhunia, A., Fei, H., Cohen, S. M. & Ott, S. (2018). Development of a UiO-Type Thin Film Electrocatalysis Platform with Redox-Active Linkers. Journal of the American Chemical Society, 140(8), 2985-2994
Open this publication in new window or tab >>Development of a UiO-Type Thin Film Electrocatalysis Platform with Redox-Active Linkers
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2018 (English)In: Journal of the American Chemical Society, ISSN 0002-7863, E-ISSN 1520-5126, Vol. 140, no 8, p. 2985-2994Article in journal (Refereed) Published
Abstract [en]

Metal–organic frameworks (MOFs) as electrocatalysis scaffolds are appealing due to the large concentration of catalytic units that can be assembled in three dimensions. To harness the full potential of these materials, charge transport to the redox catalysts within the MOF has to be ensured. Herein, we report the first electroactive MOF with the UiO/PIZOF topology (Zr(dcphOH-NDI)), i.e., one of the most widely used MOFs for catalyst incorporation, by using redox-active naphthalene diimide-based linkers (dcphOH-NDI). Hydroxyl groups were included on the dcphOH-NDI linker to facilitate proton transport through the material. Potentiometric titrations of Zr(dcphOH-NDI) show the proton-responsive behavior via the −OH groups on the linkers and the bridging Zr-μ3-OH of the secondary building units with pKa values of 6.10 and 3.45, respectively. When grown directly onto transparent conductive fluorine-doped tin oxide (FTO), 1 μm thin films of Zr(dcphOH-NDI)@FTO could be achieved. Zr(dcphOH-NDI)@FTO displays reversible electrochromic behavior as a result of the sequential one-electron reductions of the redox-active NDI linkers. Importantly, 97% of the NDI sites are electrochemically active at applied potentials. Charge propagation through the thin film proceeds through a linker-to-linker hopping mechanism that is charge-balanced by electrolyte transport, giving rise to cyclic voltammograms of the thin films that show characteristics of a diffusion-controlled process. The equivalent diffusion coefficient, De, that contains contributions from both phenomena was measured directly by UV/vis spectroelectrochemistry. Using KPF6 as electrolyte, De was determined to be De(KPF6) = (5.4 ± 1.1) × 10–11 cm2 s–1, while an increase in countercation size to n-Bu4N+ led to a significant decrease of De by about 1 order of magnitude (De(n-Bu4NPF6) = (4.0 ± 2.5) × 10–12 cm2 s–1).

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-351270 (URN)10.1021/jacs.7b13077 (DOI)000426617700044 ()29421875 (PubMedID)
Funder
Swedish Research Council
Available from: 2018-06-04 Created: 2018-06-04 Last updated: 2018-06-04Bibliographically approved
Gilbert Gatty, M., Pullen, S., Sheibani, E., Tian, H., Ott, S. & Hammarström, L. (2018). Direct evidence of catalyst reduction on dye and catalyst co-sensitized NiO photocathodes by mid-infrared transient absorption spectroscopy. Chemical Science, 9(22), 4983-4991
Open this publication in new window or tab >>Direct evidence of catalyst reduction on dye and catalyst co-sensitized NiO photocathodes by mid-infrared transient absorption spectroscopy
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2018 (English)In: Chemical Science, ISSN 2041-6520, E-ISSN 2041-6539, Vol. 9, no 22, p. 4983-4991Article in journal (Refereed) Published
Abstract [en]

Co-sensitization of molecular dyes and catalysts on semiconductor surfaces is a promising strategy to build photoelectrodes for solar fuel production. In such a photoelectrode, understanding the charge transfer reactions between the molecular dye, catalyst and semiconductor material is key to guide further improvement of their photocatalytic performance. Herein, femtosecond mid-infrared transient absorption spectroscopy is used, for the first time, to probe charge transfer reactions leading to catalyst reduction on co-sensitized nickel oxide (NiO) photocathodes. The NiO films were co-sensitized with a molecular dye and a proton reducing catalyst from the family of [FeFe](bdt)(CO)(6) (bdt = benzene-1,2-dithiolate) complexes. Two dyes were used: an organic push-pull dye denoted E2 with a triarylamine-oligothiophene-dicyanovinyl structure and a coumarin 343 dye. Upon photo-excitation of the dye, a clear spectroscopic signature of the reduced catalyst is observed a few picoseconds after excitation in all co-sensitized NiO films. However, kinetic analysis of the transient absorption signals of the dye and reduced catalyst reveal important mechanistic differences in the first reduction of the catalyst depending on the co-sensitized molecular dye (E2 or C343). While catalyst reduction is preceded by hole injection in NiO in C343-sensitized NiO films, the singly reduced catalyst is formed by direct electron transfer from the excited dye E2* to the catalyst in E2-sensitized NiO films. This change in mechanism also impacts the lifetime of the reduced catalyst, which is only ca. 50 ps in E2-sensitized NiO films but is >5 ns in C343-sensitized NiO films. Finally, the implication of this mechanistic study for the development of better co-sensitized photocathodes is discussed.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-358380 (URN)10.1039/c8sc00990b (DOI)000434693300008 ()
Funder
Swedish Energy Agency, 11645-5
Available from: 2018-08-29 Created: 2018-08-29 Last updated: 2018-08-29Bibliographically approved
Bhunia, A., Johnson, B. A., Czapla-Masztafiak, J., Sá, J. & Ott, S. (2018). Formal water oxidation turnover frequencies from MIL-101(Cr) anchored Ru(bda) depend on oxidant concentration. Chemical Communications, 54, 7770-7773
Open this publication in new window or tab >>Formal water oxidation turnover frequencies from MIL-101(Cr) anchored Ru(bda) depend on oxidant concentration
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2018 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, p. 7770-7773Article in journal (Refereed) Published
Abstract [en]

The molecular water oxidation catalyst [Ru(bda)(L)(2)] has been incorporated into pyridine-decorated MIL-101(Cr) metal-organic frameworks. The resulting MIL-101@Ru materials exhibit turnover frequencies (TOFs) up to ten times higher compared to the homogenous reference. An unusual dependence of the formal TOFs on oxidant concentration is observed that ultimately arises from differing amounts of catalysts in the MOF crystals being active.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Inorganic Chemistry Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-361265 (URN)10.1039/c8cc02300j (DOI)000438237700009 ()29926035 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg FoundationEU, European Research Council, ERC-CoG2015-681895_MOFcat
Note

De två första författarna delar förstaförfattarskapet.

Available from: 2018-10-11 Created: 2018-10-11 Last updated: 2018-10-11Bibliographically approved
Roy, S., Bhunia, A., Schuth, N., Haumann, M. & Ott, S. (2018). Light-driven hydrogen evolution catalyzed by a cobaloxime catalyst incorporated in a MIL-101(Cr) metal-organic framework. SUSTAINABLE ENERGY & FUELS, 2(6), 1148-1152
Open this publication in new window or tab >>Light-driven hydrogen evolution catalyzed by a cobaloxime catalyst incorporated in a MIL-101(Cr) metal-organic framework
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2018 (English)In: SUSTAINABLE ENERGY & FUELS, ISSN 2398-4902, Vol. 2, no 6, p. 1148-1152Article in journal (Refereed) Published
Abstract [en]

A cobaloxime H-2 evolution catalyst with a hydroxo-functionalized pyridine ligand, Co(dmgH)(2)(4-HEP)Cl [dmgH = dimethylglyoxime, 4-HEP = 4-(2-hydroxyethyl)pyridine] was immobilized on a chromium terephthalate metal-organic framework (MOF), MIL-101(Cr), to construct a MOF-catalyst hybrid which displays good photocatalytic H-2 evolution activity. The longevity of the cobaloxime catalyst is increased by MOF incorporation, but limited by the stability of the cobalt-pyridine bond under turnover conditions.

National Category
Physical Chemistry Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-357705 (URN)10.1039/c8se00072g (DOI)000434241200003 ()
Funder
Swedish Research CouncilSwedish Energy AgencyEU, European Research Council, ERC-CoG2015-681895_MOFcatWenner-Gren Foundations
Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-08-21Bibliographically approved
Mai, J., Arkhypchuk, A. I., Gupta, A. K. & Ott, S. (2018). Reductive coupling of two aldehydes to unsymmetrical E-alkenes via phosphaalkene and phosphinate intermediates. Chemical Communications, 54(52), 7163-7166
Open this publication in new window or tab >>Reductive coupling of two aldehydes to unsymmetrical E-alkenes via phosphaalkene and phosphinate intermediates
2018 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 54, no 52, p. 7163-7166Article in journal (Refereed) Published
Abstract [en]

Stilbenes with push-pull electronics are directly accessible from an electron-rich and an electron-deficient benzaldehyde in a novel reductive aldehyde cross-coupling reaction. The one-pot procedure is enabled by the oxidation of a transient phosphinite to the corresponding phosphinate which exhibits sufficient reactivity towards deactivated aldehydes.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:uu:diva-362015 (URN)10.1039/c8cc04218g (DOI)000436290100012 ()29888363 (PubMedID)
Funder
Swedish Research Council
Available from: 2018-10-05 Created: 2018-10-05 Last updated: 2018-10-05Bibliographically approved
Föhlinger, J., Maji, S., Brown, A. M., Mijangos, E., Ott, S. & Hammarström, L. (2018). Self-quenching and Slow Hole Injection May Limit the Efficiency in NiO-based Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 122(25), 13902-13910
Open this publication in new window or tab >>Self-quenching and Slow Hole Injection May Limit the Efficiency in NiO-based Dye-Sensitized Solar Cells
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2018 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 122, no 25, p. 13902-13910Article in journal (Refereed) Published
Abstract [en]

A series of bis-tridentate ruthenium complexes was designed to feature opposite localizations of their lowest metal-to-ligand charge transfer (MLCT) excited states, relative to a carboxylic acid that served as a binding group to mesoporous NiO. The purpose was to study the effect of MLCT direction on the rates of hole injection into NiO and subsequent charge recombination. Surprisingly, femtosecond-transient absorption spectroscopy showed that the two heteroleptic, cyclometalated complexes of this series did not inject holes into NiO, but their excited states were nevertheless quenched in a rapid process (on the time scale of hundreds of picoseconds). An identical result was obtained for the dyes on nonreactive ZrO2 and we therefore attribute the short MLCT lifetime to self-quenching, due the high surface concentrations of the dyes. We further show that self-quenching on this time scale can potentially compete with hole injection also for functional NiO sensitizers. A ruthenium polypyridine complex, which has previously been used for NiO-based solar cells, was shown to inject holes only very slowly (τ ≈ 5 ns), in contrast to the common notion that hole injection in dye-NiO systems is ultrafast (predominantly subpicosecond time scale). The hole injection yield was estimated to only ca. 20%, which matches the reported APCE value of the corresponding device [Freys, J. C.; Gardner, J. M.; D’Amario, L.; Brown, A. M.; Hammarström, L. Dalton Trans. 2012, 41, 13105]. Therefore, we suggest that slow injection and self-quenching might be a reason for the low photovoltaic performance of some p-type dye-sensitized solar cells.

National Category
Physical Chemistry
Research subject
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-343442 (URN)10.1021/acs.jpcc.8b01016 (DOI)000437811500078 ()
Funder
Swedish Research Council, 2014-5921Swedish Energy Agency, 11674-5Knut and Alice Wallenberg Foundation, 2011.0067
Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2018-09-21Bibliographically approved
Schlotthauer, T., Parada, G. A., Goerls, H., Ott, S., Jaeger, M. & Schubert, U. S. (2017). Asymmetric Cyclometalated RuII Polypyridyl-Type Complexes with Π-Extended Carbanionic Donor Sets. Inorganic Chemistry, 56(14), 7720-7730
Open this publication in new window or tab >>Asymmetric Cyclometalated RuII Polypyridyl-Type Complexes with Π-Extended Carbanionic Donor Sets
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2017 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 56, no 14, p. 7720-7730Article in journal (Refereed) Published
Abstract [en]

A series of novel cyclometalated Ru-II complexes were investigated featuring the tridentate dqp ligand platform (dqp is 2,6-di(quinolin-8-yl)pyridine), in order to utilize the octahedral coordination mode around the Ru center to modulate the electrochemical and photophysical properties. The heteroleptic complexes feature C-1 symmetry due to symmetry breaking by the peripheral five- or six-membered carbanionic chelate (phenyl, naphthyl, or anthracenyl units). The chelation mode is controlled by the steric effects and C-H activation selectivity of the ligand, which prompted the development of a general synthesis protocol. The optimized conditions to achieve high overall yields (55-75%) involve NaHCO3 as the base and an simplified purification protocol: i.e., facile chromatographic separation using commercially available amino-functionalized silica applying nonaqueous salt-free conditions to omit the necessity of counterion exchange. The structural, photophysical, and electrochemical properties were studied in depth, and the results were corroborated by density functional theory (DFT) calculations. Steady state and time-resolved spectroscopy revealed red-shifted absorption (up to 750 run) and weak IR emission (800-1000 nm) combined with prolonged emission lifetimes (up to 20 ns) in comparison to classical tpy-based (tpy is 2,2':6',2 ''-terpyridine) complexes. An enhanced stability was observed by blocking the reactive positions of the carbanionic ligand framework, while the reactive positions may be exploited for further functionalization.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-332419 (URN)10.1021/acs.inorgchem.7b00392 (DOI)000405972200018 ()
Funder
Swedish Energy AgencyKnut and Alice Wallenberg Foundation
Note

Title in WoS: Asymmetric Cyclometalated Ru-II Polypyridyl-Type Complexes with pi-Extended Carbanionic Donor Sets

Available from: 2017-11-02 Created: 2017-11-02 Last updated: 2017-12-28Bibliographically approved
Roy, S., Pascanu, V., Pullen, S., Gonzalez Miera, G., Martin-Matute, B. & Ott, S. (2017). Catalyst accessibility to chemical reductants in metal–organic frameworks. Chemical Communications, 53(22), 3257-3260
Open this publication in new window or tab >>Catalyst accessibility to chemical reductants in metal–organic frameworks
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2017 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 53, no 22, p. 3257-3260Article in journal (Refereed) Published
Abstract [en]

A molecular H2-evolving catalyst, [Fe2(cbdt)(CO)6] ([FeFe], cbdt = 3-carboxybenzene-1,2-dithiolate), has been attached covalently to an amino-functionalized MIL-101(Cr) through an amide bond. Chemical reduction experiments reveal that the MOF channels can be clogged by ion pairs that are formed between the oxidized reductant and the reduced catalyst. This effect is lessened in MIL-101-NH-[FeFe] with lower [FeFe] loadings. On longer timescales, it is shown that large proportions of the [FeFe] catalysts within the MOF engage in photochemical hydrogen production and the amount of produced hydrogen is proportional to the catalyst loading.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-318972 (URN)10.1039/c7cc00022g (DOI)000398998500023 ()28261731 (PubMedID)
Available from: 2017-03-29 Created: 2017-03-29 Last updated: 2017-12-28Bibliographically approved
Johnson, B. A., Bhunia, A. & Ott, S. (2017). Electrocatalytic water oxidation by a molecular catalyst incorporated into a metal-organic framework thin film. Dalton Transactions, 46(5), 1382-1388
Open this publication in new window or tab >>Electrocatalytic water oxidation by a molecular catalyst incorporated into a metal-organic framework thin film
2017 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 5, p. 1382-1388Article in journal (Refereed) Published
Abstract [en]

A molecular water oxidation catalyst, [Ru(tpy)(dcbpy)(OH2)](ClO4)(2) (tpy = 2,2': 6',2''-terpyridine, dcbpy = 2,2'-bipyridine- 5,5'-dicarboxylic acid) [1], has been incorporated into FTO-grown thin films of UiO-67 (UiO = University of Oslo), by post-synthetic ligand exchange. Cyclic voltammograms (0.1 M borate buffer at pH = 8.4) of the resulting UiO67-[RuOH2]@ FTO show a reversible wave associated with the Ru-III/II couple in the anodic scan, followed by a large current response that arises from electrocatalytic water oxidation beyond 1.1 V vs. Ag/AgCl. Water oxidation can be observed at an applied potential of 1.5 V over the timescale of hours with a current density of 11.5 mu A cm(-2). Oxygen evolution was quantified in situ over the course of the experiment, and the Faradaic efficiency was calculated as 82%. Importantly, the molecular integrity of [1] during electrocatalytic water oxidation is maintained even on the timescale of hours under turnover conditions and applied voltage, as evidenced by the persistence of the wave associated with the Ru-III/II couple in the CV. This experiment highlights the capability of metal organic frameworks like UiO-67 to stabilize the molecular structure of catalysts that are prone to form higher clusters in homogenous phase.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-319681 (URN)10.1039/c6dt03718frsc.li/dalton (DOI)000395442700005 ()27845800 (PubMedID)
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Available from: 2017-04-07 Created: 2017-04-07 Last updated: 2017-11-29Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-1691-729X

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