Comparison of cobalt and manganese in the chemistry of water oxidation

McAlpin, J. Gregory; Stich, Troy A.; Casey, William H.; Britt, R. David

doi:10.1016/j.ccr.2012.04.039

Cited by 88 publications

(57 citation statements)

References 56 publications

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“…Much effort has been devoted to the development of earth-abundant water oxidation catalysts (11)(12)(13)(14), including a recently reported completely organic catalyst (15). Less attention has been paid to the development of earth-abundant sensitizers-an important problem for WS-DSPECs where absorber-to-catalyst ratios can exceed 1,000:1.…”

mentioning

confidence: 99%

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Swierk¹,

Méndez-Hernández

McCool³

et al. 2015

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

138

107

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Solar fuel generation requires the efficient capture and conversion of visible light. In both natural and artificial systems, molecular sensitizers can be tuned to capture, convert, and transfer visible light energy. We demonstrate that a series of metal-free porphyrins can drive photoelectrochemical water splitting under broadband and red light (λ > 590 nm) illumination in a dye-sensitized TiO2 solar cell. We report the synthesis, spectral, and electrochemical properties of the sensitizers. Despite slow recombination of photoinjected electrons with oxidized porphyrins, photocurrents are low because of low injection yields and slow electron self-exchange between oxidized porphyrins. The free-base porphyrins are stable under conditions of water photoelectrolysis and in some cases photovoltages in excess of 1 V are observed.

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mentioning

confidence: 99%

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Swierk¹,

Méndez-Hernández

McCool³

et al. 2015

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

138

107

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“…33,94 While Co(II) is most commonly found in a high spin configuration, higher oxidation states of Co are often low spin whereas higher oxidation states of Mn exhibit usually still high spin configurations. 95 The weakening of the metaloxygen bond (mentioned in Spin population and molecular orbital analysis) is more pronounced for Co(IV)-O than for Mn(IV)-O, 85 which has one electron less occupying π-antibonding orbitals compared to low spin Co(IV).…”

Section: Discussionmentioning

confidence: 99%

What Influences the Water Oxidation Activity of a Bioinspired Molecular Co^II₄O₄ Cubane? An In-Depth Exploration of Catalytic Pathways

Hodel

Luber

2016

ACS Catal.

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Solar light to chemical energy conversion is an important topic of research due to global climate change and an increasing shortage of fossil fuels. Artificial photosynthesis, as a possible solution to these issues, is strongly dependent on efficient water oxidation. The exact way in which molecular water oxidation catalysts (WOCs), in particular biomimetic cubanes, perform the task of splitting water into oxygen, protons, and electrons still remains unclear to a large extent. We investigated the reaction mechanism of the recently presented first Co(II)-based WOC, [CoII4(hmp)4( -OAc)2( 2-OAc)2(H2O)2] (hmp = 2-(hydroxymethyl)pyridine) [Evangelisti, F.; Güttinger, R.; Moré, R.; Luber, S.; Patzke, G. R. J. Am. Chem. Soc. 2013, 135, 18734−18737], which is one of the rare stable homogeneous cubane-type WOCs and the design of which has been inspired by nature's oxygen evolving complex of photosystem II (PSII). Two possible different catalytic cycles have been envisioned: A single-site pathway involving one cobalt center and a water attack on an oxo ligand or, alternatively, an oxo-oxo coupling pathway where, after the replacement of an acetate ligand by water, two terminal oxo ligands of the cubane couple and are released as O2. Using density functional theory and an explicit solvation shell, we compare relative free energies of all states of the catalytic pathways, also with different ligand environments, and analyze the stability and reactivity of each catalytic state in detail. Furthermore, we compute barriers and reaction paths for water attack and O2 release steps. With this knowledge at hand, we propose possibilities to tune catalytic activity paving the way to informed design of high-performance PSII mimics.

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“…The electrochemical performance of oxides for OER follows the order, IrO 2 4RuO 2 4Co 3 O 4 and Ni-containing cobalt oxides4Fe, Pb, Mn containing oxides. Among the numerous low-cost oxides investigated, cobalt oxides are promising for both OER and ORR [14][15][16][17][18] and have been largely studied as stable electrocatalysts for OER in highly alkaline solutions 19 . For example, spinel NiCo 2 O 4 and Co 3 O 4 have been found by several groups to show good efficiency and long-term performance, but they underperform relative to IrO 2 (ref.…”

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confidence: 99%

Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions

et al. 2014

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Development of efficient, affordable electrocatalysts for the oxygen evolution reaction and the oxygen reduction reaction is critical for rechargeable metal-air batteries. Here we present lithium cobalt oxide, synthesized at 400°C (designated as LT-LiCoO 2 ) that adopts a lithiated spinel structure, as an inexpensive, efficient electrocatalyst for the oxygen evolution reaction. The catalytic activity of LT-LiCoO 2 is higher than that of both spinel cobalt oxide and layered lithium cobalt oxide synthesized at 800°C (designated as HT-LiCoO 2 ) for the oxygen evolution reaction. Although LT-LiCoO 2 exhibits poor activity for the oxygen reduction reaction, the chemically delithiated LT-Li 1 À x CoO 2 samples exhibit a combination of high oxygen reduction reaction and oxygen evolution reaction activities, making the spinel-type LTLi 0,5 CoO 2 a potential bifunctional electrocatalyst for rechargeable metal-air batteries. The high activities of these delithiated compositions are attributed to the Co 4 O 4 cubane subunits and a pinning of the Co 3 þ /4 þ :3d energy with the top of the O 2 À :2p band.

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Comparison of cobalt and manganese in the chemistry of water oxidation

Cited by 88 publications

References 56 publications

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

What Influences the Water Oxidation Activity of a Bioinspired Molecular Co^II₄O₄ Cubane? An In-Depth Exploration of Catalytic Pathways

Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions

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Comparison of cobalt and manganese in the chemistry of water oxidation

Cited by 88 publications

References 56 publications

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

Metal-free organic sensitizers for use in water-splitting dye-sensitized photoelectrochemical cells

What Influences the Water Oxidation Activity of a Bioinspired Molecular CoII4O4 Cubane? An In-Depth Exploration of Catalytic Pathways

Spinel-type lithium cobalt oxide as a bifunctional electrocatalyst for the oxygen evolution and oxygen reduction reactions

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What Influences the Water Oxidation Activity of a Bioinspired Molecular Co^II₄O₄ Cubane? An In-Depth Exploration of Catalytic Pathways