Evaluation of iron-based electrocatalysts for water oxidation – an on-line mass spectrometry approach

Kottrup, Konstantin G.; Hetterscheid, Dennis G. H.

doi:10.1039/c5cc10092e

Cited by 27 publications

(36 citation statements)

References 37 publications

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“…Online Electrochemical Mass Spectrometry (OLEMS) Measurements . In addition to EQCM experiments to probe the homogeneous nature of the (modified) complexes, OLEMS measurements were performed to provide access to real‐time information about the gaseous products that are formed at the electrode surface. Since this technique combines classical electrochemical methods with on‐line mass spectrometry, such tandem measurements also shed light on the onset potentials of these reactions and on possible decomposition pathways.…”

Section: Resultsmentioning

confidence: 99%

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

et al. 2020

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Based on previous work that identified iridium(III) Cp* complexes containing a C,N‐bidentate chelating triazolylidene‐pyridyl ligand (Cp* = pentamethylcyclopentadienyl, C5Me5–) as efficient molecular water oxidation catalysts, a series of new complexes based on this motif has been designed and synthesized in order to improve catalytic activity. Modifications include specifically the introduction of electron‐donating substituents into the pyridyl unit of the chelating ligand (H, a; 5‐OMe, b; 4‐OMe, c; 4‐tBu, d; 4‐NMe2, e), as well as electronically active substituents on the triazolylidene C4 position (H, 8; COOEt, 9; OEt, 10; OH, 11; COOH, 12). Chemical oxidation using cerium ammonium nitrate (CAN) indicates a clear structure‐activity relationship with electron‐donating groups enhancing catalytic turnover frequency, especially when the donor substituent is positioned on the triazolylidene ligand fragment (TOFmax = 2500 h–1 for complex 10 with a MeO group on pyr and a OEt‐substituted triazolylidene, compared to 700 h–1 for the parent benchmark complex without substituents). Electrochemical water oxidation does not follow the same trend, and reveals that complex 8b without a substituent on the triazolylidene fragment outperforms complex 10 by a factor of 5, while in CAN‐mediated chemical water oxidation, complex 10 is twice more active than 8b. This discrepancy in catalytic activity is remarkable and indicates that caution is needed when benchmarking iridium water oxidation catalysts with chemical oxidants, especially when considering that application in a potential device will most likely involve electrocatalytic water oxidation.

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Section: Resultsmentioning

confidence: 99%

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

et al. 2020

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“…OLEMS experiments were important to establish that cis-iron cyclam complexes are active in the water oxidation reaction, whereas the trans complexes are not. 37 Electrolysis of water at 1.9 V versus RHE in the presence of 1.1 mM [cis-Fe(cyclam)(Cl) 2 ]Cl resulted in the immediate formation of dioxygen. Despite the fact that OLEMS experiments typically show a lag time, the initial rate of oxygen evolution determined by mass spectrometry clearly showed that the turnover frequency is maximal at the very beginning of the electrolysis experiment.…”

Section: Mass Spectrometry Techniquesmentioning

confidence: 99%

In operando studies on the electrochemical oxidation of water mediated by molecular catalysts

Hetterscheid

2017

Chem. Commun.

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Homogeneous reactions in general are relatively easy to study with respect to heterogeneous systems since all catalytic sites are uniform and can be addressed simultaneously. The latter feature is fully out of the window in an electrochemical context, where only the few catalytic species that are sufficiently close to the electrode undergo redox reactions. Especially in the water oxidation reaction where harsh reaction conditions are employed, a clear picture of what is the active species, what products are formed, how one can steer this, and how it all depends on the exact reaction conditions is important to be able to fully unravel the key reaction paths. The combination of electrochemical experiments with on-line detection of the catalytic species and reaction products is a powerful approach to successfully address these questions. Recently, a significant progress has been made in on-line studies on molecular water oxidation catalysts during electrochemical experiments. These are reviewed here.

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“…The instantaneous evolution of dioxygen as soon as a sufficiently high potential is applied, illustrates that Ru-bpc itself is the active species in the oxygen evolution reaction at early stages of the water oxidation reaction. 78 We cannot rule out that the cymene ligand de-coordinates after prolonged electrolysis under the harsh oxidative conditions and the decrease in oxygen evolution rates after the initial burst may actually point to such an event.…”

Section: -77mentioning

confidence: 99%

Electrochemical and Spectroscopic Study of Mononuclear Ruthenium Water Oxidation Catalysts: A Combined Experimental and Theoretical Investigation

et al. 2016

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One of the key challenges in designing light-driven artificial photosynthesis devices is the optimisation of the catalytic water oxidation process. For this optimisation it is crucial to establish the catalytic mechanism and the intermediates of the catalytic cycle, yet a full description is often difficult to obtain using only experimental data. Here we consider a series of mononuclear ruthenium water oxidation catalysts of the formand its derivatives). The proposed catalytic cycle and intermediates are examined using density functional theory (DFT), radiation chemistry, spectroscopic techniques and electrochemistry to establish the water oxidation mechanism. The stability of the catalyst is investigated using Online Electrochemical Mass Spectrometry (OLEMS). The comparison between the calculated absorption spectra of the proposed intermediates with experimental ones, as well as free-energy calculations with electrochemical data, provides strong evidence for the proposed pathway: a water oxidation catalytic cycle involving four proton-coupled electron transfer (PCET) steps. The thermodynamic bottleneck is identified in the third PCET step involving the O-O bond formation. The good agreement between the optical and thermodynamic data with DFT predictions further confirms the general applicability of this methodology as a powerful tool in the characterisation of water oxidation catalysts and for the interpretation of experimental observables.2

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Evaluation of iron-based electrocatalysts for water oxidation – an on-line mass spectrometry approach

Cited by 27 publications

References 37 publications

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

Relevance of Chemical vs. Electrochemical Oxidation of Tunable Carbene Iridium Complexes for Catalytic Water Oxidation

In operando studies on the electrochemical oxidation of water mediated by molecular catalysts

Electrochemical and Spectroscopic Study of Mononuclear Ruthenium Water Oxidation Catalysts: A Combined Experimental and Theoretical Investigation

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