Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

Song, Na; Concepcion, Javier J.; Binstead, Robert A.; Rudd, Jennifer A.; Vannucci, Aaron K.; Dares, Christopher J.; Coggins, Michael K.; Meyer, Thomas J.

doi:10.1073/pnas.1500245112

Cited by 124 publications

(183 citation statements)

References 36 publications

(51 reference statements)

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“…[7] This behavior is also known for other catalysts and originates from the involvement of proton transfer in the rate-limiting step. [8] However, the [Ru(bda)(L) 2 ] family of catalysts follows a bimolecular pathway for OÀO bond formation.…”

mentioning

confidence: 71%

Water Oxidation by Ruthenium Complexes Incorporating Multifunctional Bipyridyl Diphosphonate Ligands

Xie

Shaffer

Lewandowska-Andrałojć

et al. 2016

Angew Chem Int Ed

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We describe herein the synthesis and characterization of ruthenium complexes with multifunctional bipyridyl diphosphonate ligands as well as initial water oxidation studies. In these complexes, the phosphonate groups provide redox-potential leveling through charge compensation and σ donation to allow facile access to high oxidation states. These complexes display unique pH-dependent electrochemistry associated with deprotonation of the phosphonic acid groups. The position of these groups allows them to shuttle protons in and out of the catalytic site and reduce activation barriers. A mechanism for water oxidation by these catalysts is proposed on the basis of experimental results and DFT calculations. The unprecedented attack of water at a neutral six-coordinate [Ru(IV) ] center to yield an anionic seven-coordinate [Ru(IV) -OH](-) intermediate is one of the key steps of a single-site mechanism in which all species are anionic or neutral. These complexes are among the fastest single-site catalysts reported to date.

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“…Under these conditions, MeCN is coordinated to the Ru(II) form of the catalyst, Scheme 4, with pK a = 2.4 for the open-arm −COOH chelate. 11 The first quasi-reversible wave at E 1/2 = 0.62 V vs the saturated calomel electrode (SCE; 0.24 V vs NHE) arises from a 2e − /2H + Ru IV/II couple at this pH. 16 Oxidation of the Ru(II) form of the complex is accompanied by exchange of …”

Section: Methodsmentioning

confidence: 99%

“…It also highlights the role of electron transfer mediation at the oxide. 11 The larger overpotential for water oxidation at ITO−RuP 2+ in Figure 8 is due to the higher potential of the relay couple with E o = 1.07 V for ITO−RuP 3+/2+ compared to E o = 0.78 V for the Ru V/IV (O) +/0 couple.…”

Section: Acs Catalysismentioning

confidence: 96%

Electron Transfer Mediator Effects in the Oxidative Activation of a Ruthenium Dicarboxylate Water Oxidation Catalyst

et al. 2015

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The mechanism of electrocatalytic water oxidation by the water oxidation catalyst, ruthenium 2,2′-bipyridine-6,6′-dicarboxylate (bda) bis-isoquinoline (isoq), [Ru(bda)(isoq) 2 ], 1, at metal oxide electrodes has been investigated. At indium-doped tin oxide (ITO), diminished catalytic currents and increased overpotentials are observed compared to glassy carbon (GC). At pH 7.2 in 0.5 M NaClO 4 , catalytic activity is enhanced by the addition of [Ru(bpy) 3 ] 2+ (bpy = bipyridine) as a redox mediator. Enhanced catalytic rates are also observed at ITO electrodes derivatized with the surface-bound phosphonic acid derivative [Ru(4,4′-(PO 3 H 2 ) 2 bpy)(bpy) 2 ] 2+ , RuP 2+ . Controlled potential electrolysis with measurement of O 2 at ITO with and without surface-bound RuP 2+ confirm that water oxidation catalysis occurs. Remarkable rate enhancements are observed with added acetate and phosphate, consistent with an important mechanistic role for atom-proton transfer (APT) in the rate-limiting step as described previously at GC electrodes.

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“…44−46 In a recent mechanistic study on water oxidation by an analogous Ru II (bda) catalyst, water oxidation was shown to occur following oxidation to Ru V (O) + and rate-limiting O atom transfer to water. 31 In the surface-bound assembly under steady-state photolysis conditions, assuming the same ratelimiting step, the assembly would exist as FTO|nanoSnO 2 | TiO 2 (3 nm)|-Ru III -Ru V (O) + , eq 1. Under these conditions, chromophore decomposition as −Ru III presumably competes with rate-limiting water oxidation, explaining the loss in O 2 evolution while maintaining decreased but sustained photocurrents.…”

Section: The Journal Of Physical Chemistry Lettersmentioning

confidence: 99%

Light-Driven Water Splitting with a Molecular Electroassembly-Based Core/Shell Photoanode

Sherman

Ashford

Lapides

et al. 2015

J. Phys. Chem. Lett.

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124

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An electrochemical procedure for preparing chromophore-catalyst assemblies on oxide electrode surfaces by reductive vinyl coupling is described. On core/shell SnO 2 /TiO 2 nanoparticle oxide films, excitation of the assembly with 1 sun (100 mW cm −2 ) illumination in 0.1 M H 2 PO 4 − /HPO 4 2− at pH 7 with an applied bias of 0.4 V versus SCE leads to water splitting in a DSPEC with a Pt cathode. Over a 5 min photolysis period, the core/shell photoanode produced O 2 with a faradaic efficiency of 22%. Instability of the surface bound chromophore in its oxidized state in the phosphate buffer leads to a gradual decrease in photocurrent and to the relatively modest faradaic efficiencies.T he dye-sensitized photoelectrosynthesis cell (DSPEC), which incorporates electrode architectures similar to those used in dye-sensitized solar cells (DSSCs), 1,2 integrates molecular chromophores and catalysts with a high band gap semiconductor oxide electrode for water splitting into O 2 and H 2 or for CO 2 reduction to a reduced carbon fuel. 3−7 In exploiting the initial, seminal work of Fujishima and Honda, 8 a DSPEC integrates molecular light absorption and catalysis with the bandgap properties of oxide semiconductors to extend light absorption into the visible and utilize chemical catalysis of solar fuel half reactions. A variety of DSPEC configurations have appeared in the literature, 9−15 but low overall solar energy conversion efficiencies as well as poor long-term stability remain a central challenge.Examples of DSPEC water splitting have been reported based on carboxylate-, 13 phosphonate-, 14,16 or siloxyl-derivatized 12 surface binding and by preformed, covalently linked chromophore-catalyst assemblies. 9 Additional surface binding strategies have been explored including embedding molecular components in polymer film coatings 10,15 and "layer-by-layer" assemblies with Zr(IV)-phosphonate bridges. 17,18 Use of preformed assemblies offers synthetic control and well-defined structures but, typically, requires laborious multiple-step synthetic procedures resulting in low overall yields. Based on earlier procedures for preparing cross-linked electropolymerized films by reductive coupling of vinylderivatized polypyridyl complexes, 19 electroassembly offers the advantage of on-surface synthesis without prior covalent bond formation.Electropolymerization has been used to form electroactive thin films on a variety of conducting and semiconducting substrates, including metal oxides. 20,21 It provides a basis for preparing controlled surface coverages, 22,23 multicomponent and layered structures, 19,22,23 and electrocatalytic films, 21,24,25 including films for electrocatalytic water oxidation. 22 Photoelectrochemical oxidation of iodide and hydroquinone in electropolymerized Ru(II) polypyridyl films has also been reported. 26 In a recent report, we described an extension of the vinyl reduction/C−C coupling chemistry used in cross-linked films to the preparation of electroassemblies within the cavities of nanoparticle and mesoscopi...

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“…Also, a direct interaction of OH -with the Ru high valent reactive species at high pH has also been shown to enhance kinetics. 37,38 Using the knowledge accumulated over recent years, we have designed new Ru complexes that could potentially benefit from most of the considerations mentioned above. …”

Section: Introductionmentioning

confidence: 99%

Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex

et al. 2015

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Base-enhanced catalytic water oxidation by a carboxylate–bipyridine Ru(II) complex

Cited by 124 publications

References 36 publications

Water Oxidation by Ruthenium Complexes Incorporating Multifunctional Bipyridyl Diphosphonate Ligands

Electron Transfer Mediator Effects in the Oxidative Activation of a Ruthenium Dicarboxylate Water Oxidation Catalyst

Light-Driven Water Splitting with a Molecular Electroassembly-Based Core/Shell Photoanode

Intramolecular Proton Transfer Boosts Water Oxidation Catalyzed by a Ru Complex

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