A cobalt(ii) quaterpyridine complex as a visible light-driven catalyst for both water oxidation and reduction

Leung, Chi‐Fai; Ng, Siu Mui; Ko, Chi‐Chiu; Man, Wai‐Lun; Wu, Jiashou; Chen, Lingjing; Lau, Tai‐Chu

doi:10.1039/c2ee21840b

Cited by 184 publications

(116 citation statements)

References 45 publications

(47 reference statements)

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“…1 top and an I2M mechanism is found when the favored species resemble those of the oxyl radical form depicted in the lower part of Figure 1 Recently several first row transition metal complexes have been reported as catalysts for the water oxidation reaction. [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] While these catalysts are of interest because of their high abundance and low toxicity, their performance is much poorer than their Ru or Ir analogues, and in addition their mechanistic pathways are in most cases basically unknown. [28][29][30][41][42][43] We have very recently reported a new complex based on Cu, containing the amidate ligand OPBAN that can carry out the water oxidation reaction in a very efficient manner.…”

Section: Introductionmentioning

confidence: 99%

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

et al. 2017

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Section: Introductionmentioning

confidence: 99%

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

et al. 2017

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“…[1][2][3][4][5][6][7][8][9] The bottleneck in artificial photosynthesis is water oxidation (2 H 2 O!O 2 + 4 H + + 4 e À ), which can provide an unlimited source of protons and electrons for the production of solar fuels such as H 2 , CO (CO 2 + 2 H + + 2 e À !CO + H 2 O), or methanol (CO 2 + 6 H + + 6 e À !CH 3 OH + H 2 O). [16,17] So far a number of Co, [18][19][20][21][22][23][24][25] Mn, [26][27][28][29][30] Fe, [31][32][33] and Cu [34][35][36] WOCs have been reported. However, to be economically viable, the catalysts should be made from inexpensive, earth-abundant materials.…”

Section: Introductionmentioning

confidence: 99%

Efficient Chemical and Visible‐Light‐Driven Water Oxidation using Nickel Complexes and Salts as Precatalysts

Chen

et al. 2013

ChemSusChem

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Chemical and visible-light-driven water oxidation catalyzed by a number of Ni complexes and salts have been investigated at pH 7-9 in borate buffer. For chemical oxidation, [Ru(bpy)3](3+) (bpy = 2,2'-bipyridine) was used as the oxidant, with turnover numbers (TONs) >65 and a maximum turnover frequency (TOFmax) >0.9 s(-1). Notably, simple Ni salts such as Ni(NO3 )2 are more active than Ni complexes that bear multidentate N-donor ligands. The Ni complexes and salts are also active catalysts for visible-light-driven water oxidation that uses [Ru(bpy)3](2+) as the photosensitizer and S2 O8 (2-) as the sacrificial oxidant; a TON>1200 was obtained at pH 8.5 by using Ni(NO3)2 as the catalyst. Dynamic light scattering measurements revealed the formation of nanoparticles in chemical and visible-light-driven water oxidation by the Ni catalysts. These nanoparticles aggregated during water oxidation to form submicron particles that were isolated and shown to be partially reduced β-NiOOH by various techniques, which include SEM, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, XRD, and IR spectroscopy. These results suggest that the Ni complexes and salts act as precatalysts that decompose under oxidative conditions to form an active nickel oxide catalyst. The nature of this active oxide catalyst is discussed.

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“…Recently, such efforts have resulted in the development of a significant number of systems based on single-site and multinuclear transition metal complexes including Mn, Fe, Co, Cu, Ru, and Ir (9-15). Examples of cobalt-based molecular catalysts include a cobalt phthalocyanine (16), a cobalt "hangman" corrole (17), multipyridine cobalt complexes (18,19), a dinuclear Co-peroxo species (20), and most recently, Co-porphyrins (21). Determining if these molecular complexes retain their homogenous nature during catalysis or merely act as precursors of truly active heterogeneous species such as films and nanoparticles has proven to be problematic (8,22,23).…”

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Efficient water oxidation catalyzed by homogeneous cationic cobalt porphyrins with critical roles for the buffer base

Wang

Groves

2013

Proc. Natl. Acad. Sci. U.S.A.

325

306

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A series of cationic cobalt porphyrins was found to catalyze electrochemical water oxidation to O 2 efficiently at room temperature in neutral aqueous solution. 10,15,porphyrin, with a highly electron-deficient meso-dimethylimidazolium porphyrin, was the most effective catalyst. The O 2 formation rate was 170 nmol·cm −2 ·min −1 (k obs = 1.4 × 10 3 s −1 ) with a Faradaic efficiency near 90%. Mechanistic investigations indicate the generation of a Co IV -O porphyrin cation radical as the reactive oxidant, which has accumulated two oxidizing equivalents above the Co III resting state of the catalyst. The buffer base in solution was shown to play several critical roles during the catalysis by facilitating both redox-coupled proton transfer processes leading to the reactive oxidant and subsequent O-O bond formation. More basic buffer anions led to lower catalytic onset potentials, extending below 1 V. This homogeneous cobalt-porphyrin system was shown to be robust under active catalytic conditions, showing negligible decomposition over hours of operation. Added EDTA or ion exchange resin caused no catalyst poisoning, indicating that cobalt ions were not released from the porphyrin macrocycle during catalysis. Likewise, surface analysis by energy dispersive X-ray spectroscopy of the working electrodes showed no deposition of heterogeneous cobalt films. Taken together, the results indicate that Co-5,10,15,20-tetrakis-(1,3-dimethylimidazolium-2-yl)porphyrin is an efficient, homogeneous, single-site water oxidation catalyst.ater oxidation is a key step in photosynthesis that efficiently harvests and stores solar energy (1). The oxidation of H 2 O to O 2 is a four-electron, four-proton process in which O-O bond formation is the key chemical step. In photosystem II, these proton-coupled electron transfers (PCETs) occur via a tyrosine at the Mn 4 Ca oxygen-evolving complex (2). An important thermodynamic aspect of photosynthesis is the efficient conversion of photonic energy to electrical potential, thus providing 99% of the driving force required to convert CO 2 to carbohydrates (Eqs. 1 and 2):andThe development of synthetic catalysts that can mediate water oxidation under mild conditions with a minimal energy cost has become an appealing challenge for chemists (3-7). Among various approaches, homogeneous molecular catalysts have shown attractive features such as controllable redox properties, ease of investigating reaction mechanisms, and strategies for the characterization of reactive intermediates (8,9). Recently, such efforts have resulted in the development of a significant number of systems based on single-site and multinuclear transition metal complexes including Mn, Fe, Co, Cu, Ru, and Ir (9-15). Examples of cobalt-based molecular catalysts include a cobalt phthalocyanine (16), a cobalt "hangman" corrole (17), multipyridine cobalt complexes (18, 19), a dinuclear Co-peroxo species (20), and most recently, Co-porphyrins (21). Determining if these molecular complexes retain their homogenous nature during catalysis or ...

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A cobalt(ii) quaterpyridine complex as a visible light-driven catalyst for both water oxidation and reduction

Cited by 184 publications

References 45 publications

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

Single Electron Transfer Steps in Water Oxidation Catalysis. Redefining the Mechanistic Scenario

Efficient Chemical and Visible‐Light‐Driven Water Oxidation using Nickel Complexes and Salts as Precatalysts

Efficient water oxidation catalyzed by homogeneous cationic cobalt porphyrins with critical roles for the buffer base

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