Activation Energies in Computational Chemistry—A Case Study

Busch, Michael; Ahlberg, Elisabet; Panas, Itai

doi:10.1002/9781118166123.ch4

Cited by 2 publications

(10 citation statements)

References 74 publications

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“…Applying this ansatz the activation energy was found to be of the order of 0.3 eV. 61 Constrained tracking of the minimum potential energy path from the dioxo to peroxo structures are shown in Fig. 7 together with the harmonic oscillator approximation described in ref.…”

Section: Resultsmentioning

confidence: 99%

“…In a recent study the problem of accessing the transition state of the O-O bond formation step was addressed. 61 The transition state itself was argued to not be directly accessible by DFT due to the multi-configurational nature of the wavefunction close to the non-avoided crossing. Instead the activation energy was estimated from the crossing of the harmonic oscillator potentials along the vibrational modes of reactant and product, resulting in the O-O bond formation.…”

Section: Resultsmentioning

confidence: 99%

“…7 together with the harmonic oscillator approximation described in ref. 61. Associated with this transition is the breaking of the MnQO double bonds.…”

Section: Resultsmentioning

confidence: 99%

“…4 12 The low activation barrier was partly attributed to the flexibility of the catalyst supporting the intramolecular O-O bond formation. 61 The final two steps of the mechanistic cycle comprise the release of 3 O 2 by consequent breaking of the Mn-peroxy bonds and replacing them with water. This reaction is found to occur Fig.…”

Section: Resultsmentioning

confidence: 99%

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Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Busch

Ahlberg

Panas

2011

Phys. Chem. Chem. Phys.

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A complete water oxidation and oxygen evolution reaction (OER) cycle is monitored by means of density functional theory (DFT). A biomimetic model catalyst, comprising a μ-OH bridged Mn(III-V) dimer truncated by acetylacetonate ligand analogs and hydroxides is employed. The reaction cycle is divided into four electrochemical hydrogen abstraction steps followed by a series of chemical steps. The former employ the tyrosine/tyrosyl redox couple acting as electron and proton sink, thus determining the reference potential. Stripping hydrogen from water leads to the formation of two highly unstable Mn(V)=O/Mn(IV)-O˙ moieties, which subsequently combine to form a μ-peroxy O-O bond. O(2) evolution results from subsequent consecutive replacement of the remaining Mn-O bonds by water. A Zener "spintronic" type mechanism for virtually barrierless O(2) evolution is found. The applicability of DFT is discussed and extended to include the rate-limiting steps in the OER. Rather than attempting to compute transition states where KS-DFT is unreliable, an upper bound for the activation barrier of the O-O bond formation step is estimated from the hessians of the relevant intermediates.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

“…7 together with the harmonic oscillator approximation described in ref. 61. Associated with this transition is the breaking of the MnQO double bonds.…”

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

See 2 more Smart Citations

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Busch

Ahlberg

Panas

2011

Phys. Chem. Chem. Phys.

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“…The Mn (III–V) system on the other hand allows for OO bond formation at a comparably small activation barrier. A more extensive discussion of this approach to assess the activation energies for 2 TMO forming TMOOTM peroxy bonds can be found in ref .…”

Section: Oer At Manganese and Iridium Oxidesmentioning

confidence: 99%

Water Oxidation on MnO_x and IrO_x: Why Similar Performance?

2012

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The critical steps in water oxidation at a binuclear Mn(II–IV) oxide site are revisited. Ideal stabilities of intermediates are confirmed by comparing to results for a binuclear Ir(III–V) system. The latter in turn is known to be an excellent water oxidation catalyst. The inefficiency of the binuclear Mn(II–IV) site is owing to the high activation energy for the chemical step whereby MnIVO double bonds on adjacent sites are broken prior to forming the MnIIIOOMnIII peroxy moiety. A rationale for Mn(II–IV)Mn(III–V) mixed oxidation state for water oxidation catalysis, analogous to mixed transition metal oxide systems, is offered. Possible virtues of the kinetic stability of the binuclear MnIVO moiety are discussed, utilizing its oxidizing power by sidestepping oxygen evolution.

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Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution

et al. 2013

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The electrochemistry of hydrous iridium oxide films (HIROF) is revisited. Cyclic voltammograms of HIROFs display two reversible redox couples commonly assigned to the Ir(III)/Ir(IV) and Ir(IV)/Ir(V) transitions, respectively. However, compared to the first, the second redox couple has significantly less charge associated to it. This effect is interpreted as partial oxidation of Ir(IV) as limited by nearest neighbor repulsion of resulting Ir(V) sites. Thus, the redox process is divided into two steps: one preceding and one overlapping the oxygen evolution reaction (OER). Here, the "super-nernstian" pH dependence of the redox processes in the HIROF is used to expose how pH controls the overpotential for oxygen evolution, as evidenced by the complementary increased formation of Ir(V) oxide. A recently formulated binuclear mechanism for the OER is employed to illustrate how hydrogen bonding may suppress the OER, thus implicitly favoring Ir(V) oxide formation above the thermodynamic onset potential for the OER at low pH.

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Activation Energies in Computational Chemistry—A Case Study

Cited by 2 publications

References 74 publications

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Water Oxidation on MnO_x and IrO_x: Why Similar Performance?

Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution

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Activation Energies in Computational Chemistry—A Case Study

Cited by 2 publications

References 74 publications

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Electrocatalytic oxygen evolution from water on a Mn(iii–v) dimer model catalyst—A DFT perspective

Water Oxidation on MnOx and IrOx: Why Similar Performance?

Revisiting the Redox Properties of Hydrous Iridium Oxide Films in the Context of Oxygen Evolution

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Product

Resources

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Water Oxidation on MnO_x and IrO_x: Why Similar Performance?