Showing posts with label water oxidation. Show all posts
Showing posts with label water oxidation. Show all posts
Wednesday, November 9, 2016
Friday, February 5, 2016
Synthesis, Structure, Spectroscopy and Reactivity of New Heterotrinuclear Water Oxidation Catalysts
Synthesis, Structure, Spectroscopy and Reactivity of New Heterotrinuclear Water Oxidation Catalysts
Lorenzo Mognon, Sukanta Mandal, Carmen E Castillo, Jérôme Fortage, Florian Molton, Guillem Aromi, Jordi Benet-Buchholz, Carole Duboc, Marie-Noëlle Collomb and Antoni Llobet
Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04672F
Chem. Sci., 2016, Accepted Manuscript
DOI: 10.1039/C5SC04672F
Four heterotrinuclear complexes containing the ligands 3,5-bis(2-pyridyl)pyrazolate (bpp-) and 2,2’:6’,2’’-terpyridine (trpy) of general formula {[RuII(trpy)]2µ-[M(X)2(bpp)2])}(PF6)2, where M = CoII, MnII and X = Cl-, AcO- (M = CoII, X = Cl-: Ru2Co-Cl2; M = MnII, X = Cl-: Ru2Mn-Cl2; M = Co, X = AcO-: Ru2Co-OAc2; M = MnII, X = AcO-: Ru2Mn-OAc2) have been prepared for the first time. The complexes have been characterized using different spectroscopic techniques such as UV-vis and IR, and mass spectrometry. X-Ray diffraction analyses have been used to characterize the Ru2Mn-Cl2 and Ru2Mn-OAc2 complexes. Cyclic voltammograms (CV) for all four complexes in organic solvent (CH3CN or CH2Cl2) display three successive reversible oxidative waves corresponding to one-electron oxidations of each of the three metal centers. The oxidized forms of complexes Ru2Co-OAc2 and Ru2Mn-OAc2 are further characterized by EPR and UV-vis spectroscopy. The magnetic susceptibility measurements of all complexes at temperature range 2-300 K reveal paramagnetic properties due to the presence of high spin Co(II) and Mn(II) centers. The complexes Ru2Co-OAc2 and Ru2Mn-OAc2 act as pre catalysts for water oxidation reaction, since the acetato groups are easily replaced by water at pH = 7 generating the active catalysts, {[Ru(H2O)(trpy)]2(µ-[M(H2O)2(bpp)2])}4+ (M = CoII: Ru2Co-(H2O)4; M = MnII: Ru2Mn-(H2O)4). The photochemical water oxidation reaction is studied using [Ru(bpy)3]2+ as photosensitizer and Na2S2O8 as sacrificial electron acceptor at pH = 7. The Co containing complex generates 50 TON in about 10 minutes (TOFi = 0.21 s-1) whereas the Mn containing one only generates 8 TON. The water oxidation reaction of Ru2Co-(H2O)4 is further investigated using Oxone as sacrificial chemical oxidant at pH = 7. Labelled water oxidation experiments suggest that a nucleophilic attack mechanism is occurring at the Co site of the trinuclear complex with cooperative involvement of the two Ru sites, via electronic coupling through the bpp- bridging ligand and via neighboring hydrogen bonding.
Friday, November 13, 2015
Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation
Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and
Durable Catalysts for Homogeneous Water Oxidation
Mo Li,† Kazutake Takada,‡ Jonas I. Goldsmith,*,§ and Stefan Bernhard*,†
† Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States ‡ Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan § Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
Inorganic Chemistry; http://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.5b01709
Abstract:
A family of tetradentate bis(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks--[Ir(bpsa-Cy)Cl2] − and [Ir(bpsa-Ph)Cl2] −produced C1-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir(bpsaen)Cl2] − displays C2 symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir(III)/Ir(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrOx. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the C1-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrOx particles.
TOC:
Mo Li,† Kazutake Takada,‡ Jonas I. Goldsmith,*,§ and Stefan Bernhard*,†
† Department of Chemistry, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, United States ‡ Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya 466-8555, Japan § Department of Chemistry, Bryn Mawr College, Bryn Mawr, Pennsylvania 19010, United States
Inorganic Chemistry; http://pubs.acs.org/doi/pdf/10.1021/acs.inorgchem.5b01709
Abstract:
A family of tetradentate bis(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks--[Ir(bpsa-Cy)Cl2] − and [Ir(bpsa-Ph)Cl2] −produced C1-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir(bpsaen)Cl2] − displays C2 symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir(III)/Ir(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrOx. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the C1-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrOx particles.
TOC:
Thursday, November 12, 2015
Efficient Light-Driven Water Oxidation Catalysis by Dinuclear Ruthenium Complexes
Dr. Serena Berardi, Dr. Laia Francas, Sven Neudeck, Dr. Somnath Maji, Dr. Jordi Benet-Buchholz, Prof. Dr. Franc Meyer, Prof. Dr. Antoni Llobet
Abstract
Mastering the light-induced four-electron oxidation of water to molecular oxygen is a key step towards the achievement of overall water splitting to produce alternative solar fuels. In this work, we report two rugged molecular pyrazolate-based diruthenium complexes that efficiently catalyze visible-light-driven water oxidation. These complexes were fully characterized both in the solid state (by X-ray diffraction analysis) and in solution (spectroscopically and electrochemically). Benchmark performances for homogeneous oxygen production have been obtained for both catalysts in the presence of a photosensitizer and a sacrificial electron acceptor at pH 7, and a turnover frequency of up to 11.1 s−1 and a turnover number of 5300 were obtained after three successive catalytic runs. Under the same experimental conditions with the same setup, the pyrazolate-based diruthenium complexes outperform other well-known water oxidation catalysts owing to both electrochemical and mechanistic aspects.http://onlinelibrary.wiley.com/doi/10.1002/cssc.201500798/full
Monday, November 9, 2015
Determining the "Best Catalyst" Depends on the Method of Catalyst Evaluation
http://pubs.acs.org/doi/abs/10.1021/jacs.5b05093
The “Best Catalyst” for Water Oxidation Depends on the Oxidation Method Employed: A Case Study of Manganese Oxides
Department
of Chemistry, University of Wisconsin—Madison, 1101 University Avenue, Madison, Wisconsin 53706, United States
J. Am. Chem. Soc., 2015, 137 (26), pp 8384–8387
DOI: 10.1021/jacs.5b05093
Abstract
Manganese oxides are a highly promising class of water-oxidation catalysts (WOCs), but the optimal MnOx formulation or polymorph is not clear from previous reports in the literature. A complication not limited to MnOx-based
WOCs is that such catalysts are routinely evaluated by different
methods, ranging from the use of a chemical oxidant such as Ce4+, photoactive mediators such as [Ru(bpy)3]2+, or electrochemical techniques. Here, we report a systematic study of nine crystalline MnOx
materials as WOCs and show that the identity of the “best” catalyst
changes, depending on the oxidation method used to probe the catalytic
activity.
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