Photo‐active Cobalt Cubane Model of an Oxygen‐Evolving Catalyst

Symes, Mark D.; Lutterman, Daniel A.; Teets, Thomas S.; Anderson, Bo; Breen, John J.; Nocera, Daniel G.

doi:10.1002/cssc.201200682

Cited by 32 publications

(27 citation statements)

References 46 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Mn is not only an abundant element, but also occurs in easily switchable oxidation states. [Co 4 O 4 ] cubanes are also shown to be active for the oxygen evolution reactions (OERs) (12,13). Nanocrytalline Co 3 O 4 (14) and Mn 2 O 3 (15) as well as "Co-Pi" and Co-phosphates (16,17) are reported to be OER catalysts.…”

Section: Artificial Photosynthesis | Water Oxidationmentioning

confidence: 99%

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides

Maitra

Naidu

Govindaraj

et al. 2013

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

167

134

View full text Add to dashboard Cite

Prompted by the early results on the catalytic activity of LiMn 2 O 4 and related oxides in the photochemical oxidation of water, our detailed study of several manganese oxides has shown that trivalency of Mn is an important factor in determining the catalytic activity. Thus, Mn 2 O 3 , LaMnO 3 , and MgMn 2 O 4 are found to be very good catalysts with turnover frequencies of 5 × 10 −4 s −1 , 4.8 × 10 −4 s −1 , and 0.8 ×10 −4 s −1 , respectively. Among the cobalt oxides, Li 2 Co 2 O 4 and LaCoO 3 -especially the latter-exhibit excellent catalytic activity, with the turnover frequencies being 9 × 10 −4 s −1 and 1.4 × 10 −3 s −1 , respectively. The common feature among the catalytic Mn and Co oxides is not only that Mn and Co are in the trivalent state, but Co 3+ in the Co oxides is in the intermediate t 2g 5 e g 1 state whereas Mn 3+ is in the t 2g 3 e g 1 state. The presence of the e g 1 electron in these Mn and Co oxides is considered to play a crucial role in the photocatalytic properties of the oxides.artificial photosynthesis | water oxidation A ny strategy for solving the energy crisis would involve the generation of fuels through artificial photosynthesis, involving the sun as the only source of energy. To complete the solar cycle, water has to act as the source of electrons, either to generate liquid fuels by the reduction of CO 2 or to yield H 2 through a complete cycle of transfer of electrons. Oxidation of water, involving the transfer of four electrons, is energy-intensive. One of the challenges with artificial photosynthesis is the development of cost-effective catalysts made of abundant elements for the efficient oxidation of water to O 2 (1). RuO 2 and IrO 2 are widely used as oxygen evolution catalysts although their availability is limited and are expensive (2-5). Oxidation of water in plants occurs in Photosystem II making use of the Mn 4 O 5 Ca cluster (6, 7) present in the protein. The structure of the water oxidation complex involves a cubic cluster with four Mn atoms bridged via oxygen atoms (8,9 Results and DiscussionWe first studied the catalytic properties of the nanoparticles of the LiMn 2 O 4 spinel, with an average crystallite size of 57 nm [see Fig. S1 for an X-ray diffraction pattern and transmission electron microscope (TEM) image], prepared by the citrate sol-gel method from their corresponding metal precursors. Oxygen evolution was studied under visible light in a standard photoexcitation system consisting of Ru(bpy) 3 2+ as the photosensitizer and Na 2 S 2 O 8 as the sacrificial electron acceptor in a solution buffered at pH = 5.8. Oxygen evolved was quantified both by a Clark-type electrode and gas chromatography. We found reasonable catalytic activity with these nanoparticles as shown in Fig. 1A. Delithiation of LiMn 2 O 4 in dilute nitric acid resulted in a decrease of unit cell volume and an increase in surface area from 20 to 55 m 2 /g (Table S1). The average crystallite size of the delithiated sample (DlLiMn 2 O 4 ) was 46 nm. Delithiation seemed to result in a slight impr...

show abstract

Section: Artificial Photosynthesis | Water Oxidationmentioning

confidence: 99%

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides

Maitra

Naidu

Govindaraj

et al. 2013

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

167

134

View full text Add to dashboard Cite

show abstract

“…The key motif of this class of compounds is the Co(III) 4 O 4 cubic core (figure 1b), [13] that was proposed as a structural model of the CaMn 4 O X oxygen evolving centre (figure 1c), operating in biological water oxidation. [14][15] More recently, [16][17] molecular cubanes were identified as models of the Cobalt phosphate/oxide catalyst (CoPi) developed by Kanan and Nocera in 2008 (figure 1d), a milestone discovery in the field of water oxidation electrocatalysis. [18][19] The water oxidation activity of 1-H was initially investigated by cyclic voltammetry experiments and under light assisted catalysis, in the presence of the well-known Ru(bpy) 3 2+ / S 2 O 8 2sacrificial system (bpy = 2,2'-bipyridine).…”

Section: Introductionmentioning

confidence: 99%

Water oxidation catalysis upon evolution of molecular Co(iii) cubanes in aqueous media

et al. 2015

View full text Add to dashboard Cite

The increasing global energy demand has stimulated great recent efforts in investigating new solutions for artificial photosynthesis, a potential source of clean and renewable solar fuel. In particular, according to the generally accepted modular approach aimed at optimising separately the different compartments of the entire process, many studies have focused on the development of catalytic systems for water oxidation to oxygen. While in recent years there have been many reports on new catalytic systems, the mechanism and the active intermediates operating the catalysis have been less investigated. Well-defined, molecular catalysts, constituted by transition metals stabilised by a suitable ligand pool, could help in solving this aspect. However, in some cases molecular species have been shown to evolve to active metal oxides that constitute the other side of this catalysis dichotomy. In this paper, we address the evolution of tetracobalt(III) cubanes, stabilised by a pyridine/acetate ligand pool, to active species that perform water oxidation to oxygen. Primary evolution of the cubane in aqueous solution is likely initiated by removal of an acetate bridge, opening the coordination sphere of the cobalt centres. This cobalt derivative, where the pristine ligands still impact on the reactivity, shows enhanced electron transfer rates to Ru(bpy)3(3+) (hole scavenging) within a photocatalytic cycle with Ru(bpy)3(2+) as the photosensitiser and S2O8(2-) as the electron sink. A more accentuated evolution occurs under continuous irradiation, where Electron Paramagnetic Resonance (EPR) spectroscopy reveals the formation of Co(ii) intermediates, likely contributing to the catalytic process that evolves oxygen. All together, these results confirm the relevant effect of molecular species, in particular in fostering the rate of the electron transfer processes involved in light activated cycles, pivotal in the design of a photoactive device.

show abstract

“…One such attempt is the preparation of a molecular triad made of the cobalt-oxo cubane [Co 4 O 4 (CO 2 Py) 2 (bpy) 4 ] 2+ (CO 2 Py = 4-carboxypyridine) to which are coordinated, via the pyridine nitrogens, two [Re(phen)(CO) 3 ] + units (phen = 1,10-phenanthroline) [54].…”

Section: A Functionalized Tetracobalt(iii) Cubane As Efficient Molecumentioning

confidence: 99%

“…Integration of molecular water oxidation catalysts into larger multicomponent systems, including electrodes or light-harvesting units, is highly desired for functional assemblies [50][51][52], however only very few attempts have been made so far to integrate such cobalt cubanes into larger, multicomponent systems [53,54]. One such attempt is the preparation of a molecular triad made of the cobalt-oxo cubane [Co 4 O 4 (CO 2 Py) 2 (bpy) 4 ] 2+ (CO 2 Py = 4-carboxypyridine) to which are coordinated, via the pyridine nitrogens, two [Re(phen)(CO) 3 ] + units (phen = 1,10-phenanthroline) [54].…”

Section: A Functionalized Tetracobalt(iii) Cubane As Efficient Molecumentioning

confidence: 99%

Artificial photosynthesis: a molecular approach to photo-induced water oxidation

Ganga

Puntoriero

2015

Pure and Applied Chemistry

View full text Add to dashboard Cite

By the use of a molecular approach we performed photo-induced water oxidation by combining different photosensitizers and catalysts in order to obtain an efficient system that pave the way to the construction of an artificial photosynthetic system. Different types of molecular catalysts, such as ruthenium and vanadium polyoxometalates or cobalt core stabilized by different organic ligands were combined with ruthenium (II) polypyridine complexes of different nuclearity, mononuclear species like [Ru(bpy) 3 ] 2+ or a tetranuclear dendrimer.

show abstract

Photo‐active Cobalt Cubane Model of an Oxygen‐Evolving Catalyst

Cited by 32 publications

References 46 publications

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides

Water oxidation catalysis upon evolution of molecular Co(iii) cubanes in aqueous media

Artificial photosynthesis: a molecular approach to photo-induced water oxidation

Contact Info

Product

Resources

About

Photo‐active Cobalt Cubane Model of an Oxygen‐Evolving Catalyst

Cited by 32 publications

References 46 publications

Importance of trivalency and the e g 1 configuration in the photocatalytic oxidation of water by Mn and Co oxides

Importance of trivalency and the e g 1 configuration in the photocatalytic oxidation of water by Mn and Co oxides

Water oxidation catalysis upon evolution of molecular Co(iii) cubanes in aqueous media

Artificial photosynthesis: a molecular approach to photo-induced water oxidation

Contact Info

Product

Resources

About

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides

Importance of trivalency and the e _g ¹ configuration in the photocatalytic oxidation of water by Mn and Co oxides