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Daniel, Q., Duan, L., Timmer, B. J. J., Chen, H., Luo, X., Ambre, R., . . . Sun, L. (2018). Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst. ACS Catalysis, 8(5), 4375-4382
Open this publication in new window or tab >>Water Oxidation Initiated by In Situ Dimerization of the Molecular Ru(pdc) Catalyst
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2018 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 8, no 5, p. 4375-4382Article in journal (Refereed) Published
Abstract [en]

The mononuclear ruthenium complex [Ru(pdc)L-3] (H(2)pdc = 2,6-pyridinedicarboxylic acid, L = N-heterocycles such as 4-picoline) has previously shown promising catalytic efficiency toward water oxidation, both in homogeneous solutions and anchored on electrode surfaces. However, the detailed water oxidation mechanism catalyzed by this type of complex has remained unclear. In order to deepen understanding of this type of catalyst, in the present study, [Ru(pdc)(py)(3)] (py = pyridine) has been synthesized, and the detailed catalytic mechanism has been studied by electrochemistry, UV-vis, NMR, MS, and X-ray crystallography. Interestingly, it was found that once having reached the Ru-IV state, this complex promptly formed a stable ruthenium dimer [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(2)](+). Further investigations suggested that the present dimer, after one pyridine ligand exchange with water to form [Ru-III(pdc)(py)(2)-O-Ru-IV(pdc)(py)(H2O)](+), was the true active species to catalyze water oxidation in homogeneous solutions.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
solar fuels, water oxidation, electrochemistry, ruthenium dimer, mechanism of O-O bond formation
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-231630 (URN)10.1021/acscatal.7b03768 (DOI)000431727300070 ()2-s2.0-85046695744 (Scopus ID)
Note

QC 20180702

Available from: 2018-07-02 Created: 2018-07-02 Last updated: 2018-07-02Bibliographically approved
Zhang, P., Chen, H., Wang, M., Yang, Y., Jiang, J., Zhang, B., . . . Sun, L. (2017). Gas-templating of hierarchically structured Ni-Co-P for efficient electrocatalytic hydrogen evolution. Journal of Materials Chemistry A, 5(16), 7564-7570
Open this publication in new window or tab >>Gas-templating of hierarchically structured Ni-Co-P for efficient electrocatalytic hydrogen evolution
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2017 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 5, no 16, p. 7564-7570Article in journal (Refereed) Published
Abstract [en]

One of the grand challenges for developing scalable and sustainable hydrogen producing systems is the lack of efficient and robust earth-abundant element based catalysts for the hydrogen evolution reaction (HER). Herein, a hierarchically structured Ni-Co-P film was fabricated via a gas templating electro-deposition method. This film exhibits remarkably high catalytic performance for the HER in 1 M KOH with respective current densities of -10 and -500 mA cm(-2) at the overpotentials of -30 and -185 mV with a Tafel slope of 41 mV dec(-1). A controlled potential electrolysis experiment demonstrates that the as-prepared Ni-Co-P film is an efficient and robust catalyst with a faradaic efficiency close to 100%. Systematic characterization suggests that the unique hierarchical structure and the mutual participation of nano-sized Ni/Co based components are responsible for the high HER catalytic activity.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2017
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-206680 (URN)10.1039/c7ta01716b (DOI)000399390300036 ()2-s2.0-85017596277 (Scopus ID)
Note

QC 20170510

Available from: 2017-05-10 Created: 2017-05-10 Last updated: 2017-05-10Bibliographically approved
Daniel, Q., Huang, P., Fan, T., Wang, Y., Duan, L., Wang, L., . . . Sun, L. (2017). Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst. Coordination chemistry reviews, 346, 206-215
Open this publication in new window or tab >>Rearranging from 6-to 7-coordination initiates the catalytic activity: An EPR study on a Ru-bda water oxidation catalyst
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2017 (English)In: Coordination chemistry reviews, ISSN 0010-8545, E-ISSN 1873-3840, Vol. 346, p. 206-215Article in journal (Refereed) Published
Abstract [en]

The coordination of a substrate water molecule on a metal centered catalyst for water oxidation is a crucial step involving the reorganization of the ligand sphere. This process can occur by substituting a coordinated ligand with a water molecule or via a direct coordination of water onto an open site. In 2009, we reported an efficient ruthenium-based molecular catalyst, Ru-bda, for water oxidation. Despite the impressive improvement in catalytic activity of this type of catalyst over the past years, a lack of understanding of the water coordination still remains. Herein, we report our EPR and DFT studies on Ru-bda (triethylammonium 3-pyridine sulfonate)(2) (1) at its Ru-III oxidation state, which is the initial state in the catalytic cycle for the O-O bond formation. Our investigation suggests that at this III-state, there is already a rearrangement in the ligand sphere where the coordination of a water molecule at the 7th position (open site) takes place under acidic conditions (pH = 1.0) to form a rare 7-coordinated Ru-III species.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Water oxidation, EPR, Ruthenium, Coordination, DFT
National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-207807 (URN)10.1016/j.ccr.2017.02.019 (DOI)000402873900014 ()2-s2.0-85014846790 (Scopus ID)
Funder
Swedish Energy AgencySwedish Research CouncilKnut and Alice Wallenberg Foundation
Note

QC 20170608

Available from: 2017-05-24 Created: 2017-05-24 Last updated: 2018-02-27Bibliographically approved
Fan, T., Duan, L., Huang, P., Chen, H., Daniel, Q., Ahlquist, M. S. G. & Sun, L. (2017). The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.. ACS Catalysis, 7(4), 2956-2966
Open this publication in new window or tab >>The Ru-tpc Water Oxidation Catalyst and Beyond: Water Nucleophilic Attack Pathway versus Radical Coupling Pathway.
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2017 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 7, no 4, p. 2956-2966Article in journal (Refereed) Published
Abstract [en]

Many Ru water oxidation catalysts have been documented in the literature. However, only a few can catalyze the O-O bond formation via the radical coupling pathway, while most go through the water nucleophilic attack pathway. Understanding the electronic effect on the reaction pathway is of importance in design of active water oxidation catalysts. The Ru-bda (bda = 2,2'-bipyridine-6,6'-dicarboxylate) catalyst is one example that catalyzes the 0-0 bond formation via the radical coupling pathway. Herein, we manipulate the equatorial backbone ligand, change the doubly charged bda(2-) ligand to a singly charged tpc- (2,2':6',2 ''-terpyridine-6-carboxylate) ligand, and study the structure activity relationship. Surprisingly, kinetics measurements revealed that the resulting Ru-tpc catalyst catalyzes water oxidation via the water nucleophilic attack pathway, which is different from the Ru-bda catalyst. The O-O bond formation Gibbs free energy of activation (AGO) at T = 298.15 K was 20.2 +/- 1.7 kcal mol(-1). The electronic structures of a series of Ru-v=O species were studied by density function theory calculations, revealing that the spin density of O-Ru=O of Ru-v=O is largely dependent on the surrounding ligands. Seven coordination configuration significantly enhances the radical character of Ru-v=O.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2017
Keywords
water oxidation, ruthenium complex, artificial photosynthesis, DFT calculation, water splitting
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-206688 (URN)10.1021/acscatal.6b03393 (DOI)000398986700082 ()
Note

QC 20170509

Available from: 2017-05-09 Created: 2017-05-09 Last updated: 2017-05-09Bibliographically approved
Wang, L., Duan, L., Ambre, R. B., Quentin, D., Chen, H., Sun, J., . . . Sun, L. (2016). A Nickel (II) PY5 Complex as an Electrocatalyst for Water Oxidation. Journal of Catalysis, 335, 72-78
Open this publication in new window or tab >>A Nickel (II) PY5 Complex as an Electrocatalyst for Water Oxidation
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2016 (English)In: Journal of Catalysis, ISSN 0021-9517, Vol. 335, p. 72-78Article in journal (Refereed) Published
Abstract [en]

A Ni-PY5 [PY5 = 2,6-bis(1,1-bis(2-pyridyl)ethyl)pyridine)] complex has been found to act as an electrocatalyst for oxidizing water to dioxygen in aqueous phosphate buffer solutions. The rate of water oxidation catalyzed by the Ni-PY5 is remarkably enhanced by the proton acceptor base HPO42−, with rate constant of 1820 M−1 s−1. Controlled potential bulk electrolysis with Ni-PY5 at pH 10.8 under an applied potential of 1.5 V vs. normal hydrogen electrode (NHE) resulted in dioxygen formation with a high faradaic efficiency over 90%. A detailed mechanistic study identifies the water nucleophilic attack pathway for water oxidation catalysis.

Place, publisher, year, edition, pages
Elsevier, 2016
Keywords
Nickel complex, Water oxidation catalyst, Electrochemistry, Water nucleophilic attack
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-173670 (URN)10.1016/j.jcat.2015.12.003 (DOI)000371098200007 ()2-s2.0-84954413362 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20160208

Available from: 2015-09-16 Created: 2015-09-16 Last updated: 2017-01-25Bibliographically approved
Wang, Y., Duan, L., Wang, L., Chen, H., Sun, J., Sun, L. & Ahlquist, M. S. G. (2015). Alkene Epoxidation Catalysts [Ru(pdc)(tpy)] and [Ru(pdc)(pybox)] Revisited: Revealing a Unique Ru-IV=O Structure from a Dimethyl Sulfoxide Coordinating Complex. ACS Catalysis, 5(7), 3966-3972
Open this publication in new window or tab >>Alkene Epoxidation Catalysts [Ru(pdc)(tpy)] and [Ru(pdc)(pybox)] Revisited: Revealing a Unique Ru-IV=O Structure from a Dimethyl Sulfoxide Coordinating Complex
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2015 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 7, p. 3966-3972Article in journal (Refereed) Published
Abstract [en]

The X-ray crystal structure of a dimethyl sulfoxide (DMSO) coordinating complex [Ru-II(kappa(2)-pdc)(tpy)(DMSO)] (H(2)pdc = 2,6-pyridyl dicarboxylic acid and tpy = 2,2':6',2 ''-terpyridine) led to the discovery of a unique Ru-IV=O configuration for the Ru-pybox (pybox = pyridine-bis(oxazoline) ligands) epoxidation catalyst by theoretical calculations. On the basis of this structure, a detailed theoretical study was conducted on the alkene epoxidation reaction using ruthenium-based epoxidation catalysts. It was found that the process of H2O2 coordination proceeded via an associative path in which one carboxylate detached. The following H2O-elimination step was found to be facilitated by the detached carboxylate group. The resulting Ru-IV=O rearranges to the species trans-2a-oxo, in which one carboxylate group is situated over the tpy ring; the trans-2a-oxo was found to have the lowest activation free energies toward alkene epoxidation. These results demonstrated the importance of the hemilabile properties of the pdc(2-) ligand for the Ru-pdc alkene epoxidation catalysts.

Keywords
epoxidation, ruthenium, DFT, hemilabile, oxidation, mechanism
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-171896 (URN)10.1021/acscatal.5b00496 (DOI)000357626800008 ()2-s2.0-84946130418 (Scopus ID)
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Note

QC 20150812

Available from: 2015-08-12 Created: 2015-08-10 Last updated: 2017-12-04Bibliographically approved
Wang, L., Fan, K., Daniel, Q., Duan, L., Li, F., Philippe, B., . . . Sun, L. (2015). Electrochemical driven water oxidation by molecular catalysts in situ polymerized on the surface of graphite carbon electrode. Chemical Communications, 51(37), 7883-7886
Open this publication in new window or tab >>Electrochemical driven water oxidation by molecular catalysts in situ polymerized on the surface of graphite carbon electrode
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2015 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 51, no 37, p. 7883-7886Article in journal (Refereed) Published
Abstract [en]

A simple strategy to immobilize highly efficient ruthenium based molecular water-oxidation catalysts on the basal-plane pyrolytic graphite electrode (BPG) by polymerization has been demonstrated. The electrode 1@BPG has obtained a high initial turnover frequency (TOF) of 10.47 s-1 at ∼700 mV overpotential, and a high turnover number (TON) up to 31600 in 1 h electrolysis.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-167712 (URN)10.1039/c5cc00242g (DOI)000353639300026 ()2-s2.0-84928537759 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20150602

Available from: 2015-06-02 Created: 2015-05-22 Last updated: 2017-12-04Bibliographically approved
Duan, L., Wang, L., Li, F., Li, F. & Sun, L. (2015). Highly Efficient Bioinspired Molecular Ru Water Oxidation Catalysts with Negatively Charged Backbone Ligands. Accounts of Chemical Research, 48(7), 2084-2096
Open this publication in new window or tab >>Highly Efficient Bioinspired Molecular Ru Water Oxidation Catalysts with Negatively Charged Backbone Ligands
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2015 (English)In: Accounts of Chemical Research, ISSN 0001-4842, E-ISSN 1520-4898, Vol. 48, no 7, p. 2084-2096Article, review/survey (Refereed) Published
Abstract [en]

The oxygen evolving complex (OEC) of the natural photosynthesis system II (PSII) oxidizes water to produce oxygen and reducing equivalents (protons and electrons). The oxygen released from PSII provides the oxygen source of our atmosphere; the reducing equivalents are used to reduce carbon dioxide to organic products, which support almost all organisms on the Earth planet. The first photosynthetic organisms able to split water were proposed to be cyanobacteria-like ones appearing ca. 2.5 billion years ago. Since then, nature has chosen a sustainable way by using solar energy to develop itself. Inspired by nature, human beings started to mimic the functions of the natural photosynthesis system and proposed the concept of artificial photosynthesis (AP) with the view to creating energy-sustainable societies and reducing the impact on the Earth environments. Water oxidation is a highly energy demanding reaction and essential to produce reducing equivalents for fuel production, and thereby effective water oxidation catalysts (WOCs) are required to catalyze water oxidation and reduce the energy loss. X-ray crystallographic studies on PSII have revealed that the OEC consists of a Mn4CaO5 cluster surrounded by oxygen rich ligands, such as oxyl, oxo, and carboxylate ligands. These negatively charged, oxygen rich ligands strongly stabilize the high valent states of the Mn cluster and play vital roles in effective water oxidation catalysis with low overpotential. This Account describes our endeavors to design effective Ru WOCs with low overpotential, large turnover number, and high turnover frequency by introducing negatively charged ligands, such as carboxylate. Negatively charged ligands stabilized the high valent states of Ru catalysts, as evidenced by the low oxidation potentials. Meanwhile, the oxygen production rates of our Ru catalysts were improved dramatically as well. Thanks to the strong electron donation ability of carboxylate containing ligands, a seven-coordinate Ru-IV species was isolated as a reaction intermediate, shedding light on the reaction mechanisms of Ru-catalyzed water oxidation chemistry. Auxiliary ligands have dramatic effects on the water oxidation catalysis in terms of the reactivity and the reaction mechanism. For instance, Ru-bda (H(2)bda = 2,2'-bipyridine-6,6'-dicarboxylic acid) water oxidation catalysts catalyze Ce-IV-driven water oxidation extremely fast via the radical coupling of two Ru-V=O species, while Ru-pda (H(2)pda = 1,10-phenanthroline-2,9-dicarboxylic acid) water oxidation catalysts catalyze the same reaction slowly via water nucleophilic attack on a Ru-V-O species. With a number of active Ru catalysts in hands, light driven water oxidation was accomplished using catalysts with low catalytic onset potentials. The structures of molecular catalysts could be readily tailored to introduce additional functional groups, which favors the fabrication of state-of-the-art Ru-based water oxidation devices, such as electrochemical water oxidation anodes and photo-electrochemical anodes. The development of efficient water oxidation catalysts has led to a step forward in the sustainable energy system.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-172721 (URN)10.1021/acs.accounts.5b00149 (DOI)000358556400032 ()26131964 (PubMedID)2-s2.0-84937690571 (Scopus ID)
Funder
Swedish Research CouncilSwedish Energy AgencyKnut and Alice Wallenberg Foundation
Note

QC 20150828

Available from: 2015-08-28 Created: 2015-08-27 Last updated: 2017-12-04Bibliographically approved
Li, F., Fan, K., Wang, L., Daniel, Q., Duan, L. & Sun, L. (2015). Immobilizing Ru(bda) Catalyst on a Photoanode via Electrochemical Polymerization for Light-Driven Water Splitting. ACS Catalysis, 5(6), 3786-3790
Open this publication in new window or tab >>Immobilizing Ru(bda) Catalyst on a Photoanode via Electrochemical Polymerization for Light-Driven Water Splitting
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2015 (English)In: ACS Catalysis, ISSN 2155-5435, E-ISSN 2155-5435, Vol. 5, no 6, p. 3786-3790Article in journal (Refereed) Published
Abstract [en]

The molecular water oxidation catalyst 1 was electrochemically polymerized on a dye-sensitized TiO2 electrode and an Fe2O3 nanorod electrode. High photocurrent densities of ca. 1.4 mA cm(-2) for poly-1+RuP@TiO2 and ca. 0.4 mA cm(-2) for poly-1@Fe2O3 were achieved under pH-neutral conditions. A kinetic isotope effect (KIE) study on poly-1+RuP@TiO2 shows that poly-1 catalyzes water oxidation on the surface of TiO2 via a radical coupling mechanism.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-170683 (URN)10.1021/cs502115f (DOI)000355964300067 ()2-s2.0-84930938630 (Scopus ID)
Funder
Swedish Energy AgencyKnut and Alice Wallenberg FoundationSwedish Research Council
Note

QC 20150707

Available from: 2015-07-07 Created: 2015-07-03 Last updated: 2017-12-04Bibliographically approved
Wang, L., Mirmohades, M., Brown, A., Duan, L., Li, F., Quentin, D., . . . Hammarstrom, L. (2015). Sensitizer-Catalyst Assemblies for Water Oxidation. Inorganic Chemistry, 54(6), 2742-2751
Open this publication in new window or tab >>Sensitizer-Catalyst Assemblies for Water Oxidation
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2015 (English)In: Inorganic Chemistry, ISSN 0020-1669, E-ISSN 1520-510X, Vol. 54, no 6, p. 2742-2751Article in journal (Refereed) Published
Abstract [en]

Two molecular assemblies with one Ru(II)-polypyridine photosensitizer covalently linked to one Ru(II)(bda)L2 catalyst (1) (bda = 2,2'-bipyridine-6,6'-dicarboxylate) and two photosensitizers covalently linked to one catalyst (2) have been prepared using a simple C-C bond as the linkage. In the presence of sodium persulfate as a sacrificial electron acceptor, both of them show high activity for catalytic water oxidation driven by visible light, with a turnover number up to 200 for 2. The linked photocatalysts show a lower initial yield for light driven oxygen evolution but a much better photostability compared to the three component system with separate sensitizer, catalyst and acceptor, leading to a much greater turnover number. Photocatalytic experiments and time-resolved spectroscopy were carried out to probe the mechanism of this catalysis. The linked catalyst in its Ru(II) state rapidly quenches the sensitizer, predominantly by energy transfer. However, a higher stability under photocatalytic condition is shown for the linked sensitizer compared to the three component system, which is attributed to kinetic stabilization by rapid photosensitizer regeneration. Strategies for employment of the sensitizer-catalyst molecules in more efficient photocatalytic systems are discussed.

National Category
Organic Chemistry
Identifiers
urn:nbn:se:kth:diva-164446 (URN)10.1021/ic502915r (DOI)000351325200028 ()25700086 (PubMedID)2-s2.0-84925014467 (Scopus ID)
Funder
Swedish Research CouncilKnut and Alice Wallenberg FoundationSwedish Energy Agency
Note

QC 20150423

Available from: 2015-04-23 Created: 2015-04-17 Last updated: 2017-12-04Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0003-1662-5817

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