Evidence for tetranuclear bis-μ-oxo cubane species in molecular iridium-based water oxidation catalysts from XAS analysis

Bartlett, Stuart A.; Sackville, Emma V.; Gibson, Emma K.; Celorrio, Verónica; Wells, Peter P.; Nachtegaal, Maarten; Sheehan, Stafford W.; Hintermair, Ulrich

doi:10.1039/c9cc02088h

Cited by 10 publications

(4 citation statements)

References 39 publications

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“…Ir species with higher valence states exhibit higher white-line intensity. [29] This behavior is in agreement with that of the reference Ir complexes in the present study (Figure 5c). Based on the white-line intensity, the initial state of 3 in the solution could be assigned to the Ir III complex.…”

Section: Mechanistic Investigationsupporting

confidence: 93%

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An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**

Kanega,

Ishida,

Sakai

et al. 2023

Angew Chem Int Ed

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For the application of CO2 as an energy storage material, a H2 storage system has been proposed based on the interconversion of CO2 and formic acid (or formate). However, energy losses are inevitable in the conversion of electrical energy to H2 as chemical energy (~70% electrical efficiency) and H2 to electrical energy (~40% electrical efficiency). To overcome these significant energy losses, we developed a system based on the interconversion of CO2 and formate for the direct storage and generation of electricity. In this paper, we report an aqueous redox flow battery system using homogeneous Ir catalysts with CO2–formate redox pair. The system exhibited a maximum discharge capacity of 10.5 mAh (1.5 Ah L‐1), capacity decay of 0.2% per cycle, and total turnover number of 2550 after 50 cycles. During charging–discharging, in situ fluorescence X‐ray absorption fine structure spectroscopy based on an online setup indicated that the active species was in a high valence state of Ir4+.

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Section: Mechanistic Investigationsupporting

confidence: 93%

“…By contrast, no significant change in the white‐line intensity was observed during the second and third charging and discharging. Ir species with higher valence states exhibit higher white‐line intensity [29] . This behavior is in agreement with that of the reference Ir complexes in the present study (Figure 5c).…”

Section: Resultsmentioning

confidence: 95%

An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**

Kanega,

Ishida,

Sakai

et al. 2023

Angew Chem Int Ed

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show abstract

“…By contrast, no significant change in the white-line intensity was observed during the second and third cycles of charging and discharging. Ir species with higher valence states exhibit higher white-line intensity 32 .…”

Section: Mechanistic Investigationmentioning

confidence: 99%

Novel aqueous flow battery using CO2 redox with a bifunctional homogeneous Ir catalyst

Kanega

Ishida

Sakai

et al. 2023

Preprint

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To suppress CO2 emissions, technologies that incorporate CO2 capture, utilization, and storage are being actively developed. Particularly, batteries using CO2 redox reactions are one of the most promising systems that combine energy conversion and storage. However, the stoichiometric reactions of CO2 and metal restrict the CO2 storage capacity of previously proposed systems. Applying catalyst-mediated CO2 redox is expected to provide flexible control of the CO2 storage capacity without dependence on the metal content. Herein, we report novel aqueous flow battery using CO2–formate redox with a bifunctional homogeneous Ir catalyst. Using of an Ir catalyst bearing a 4-hydroxy-N-methylpicolinamidate ligand was demonstrated for 50 cycles, with a maximum discharge capacity of 1.5 Ah L-1, capacity decay of 0.20% cycle-1, and total turnover number of 3,500. Furthermore, as the design concept, the CO2 storage capacity of the catalyst-based flow battery was improved more than 1000 times compared to the previously proposed system.

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“…Ir-based catalysts are of particular interest because they represent some of the most active molecular water oxidation catalysts. , Significant efforts have focused on understanding the emergence of active Ir species from precursors through the controlled degradation of placeholder ligands. X-ray absorption and Raman spectroscopies of chemically oxidized precursors and crystallography of electrochemically prepared compounds suggest that the active species is a μ-oxo-bridged Ir-dimer. − These advances have led to the development of various synthesis methods for stable and active Ir-dimer complexes and have enabled the study of structure–activity relationships. , …”

Section: Introductionmentioning

confidence: 99%

Infrared Spectroscopic Observation of Oxo- and Superoxo-Intermediates in the Water Oxidation Cycle of a Molecular Ir Catalyst

Zhang,

Chen,

Liu

et al. 2023

J. Am. Chem. Soc.

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Molecular Ir catalysts have emerged as an important class of model catalysts for understanding structure−activity relationships in water oxidation, a reaction that is central to renewable fuel synthesis. Prior efforts have mostly focused on controlling and elucidating the emergence of active species from prepared precursors. However, the development of efficient and stable molecular Ir catalysts also necessitates probing of reaction intermediates. To date, relatively little is known about the key intermediates in the cycles of the molecular Ir catalysts. Herein, we probed the catalytic cycle of a homogeneous Ir catalyst ("blue dimer") at a Au electrode/aqueous electrolyte interface by combining surface-enhanced infrared absorption spectroscopy (SEIRAS) with phase-sensitive detection (PSD). Cyclic voltammograms (CVs) from 1.4 to 1.7 V RHE (RHE = reversible hydrogen electrode) give rise to a band at ∼818 cm −1 , whereas CVs from 1.4 to ≥1.85 V RHE generate an additional band at ∼1146 cm −1 . Isotope labeling experiments indicate that the bands at ∼818 and ∼1146 cm −1 are attributable to oxo (Ir V �O) and superoxo (Ir IV − OO • ) moieties, respectively. This study establishes PSD-SEIRAS as a sensitive tool for probing water oxidation cycles at electrode/ electrolyte interfaces and demonstrates that the relative abundance of two key intermediates can be tuned by the thermodynamic driving force of the reaction.

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Evidence for tetranuclear bis-μ-oxo cubane species in molecular iridium-based water oxidation catalysts from XAS analysis

Abstract: Latest EXAFS results suggest a ‘dimer-of-dimers’ as the dominant resting state of Ir-pyalk WOCs in aqueous solution.

Cited by 10 publications

References 39 publications

An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**

An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**

Novel aqueous flow battery using CO2 redox with a bifunctional homogeneous Ir catalyst

Infrared Spectroscopic Observation of Oxo- and Superoxo-Intermediates in the Water Oxidation Cycle of a Molecular Ir Catalyst

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Evidence for tetranuclear bis-μ-oxo cubane species in molecular iridium-based water oxidation catalysts from XAS analysis

Abstract: Latest EXAFS results suggest a ‘dimer-of-dimers’ as the dominant resting state of Ir-pyalk WOCs in aqueous solution.

Cited by 10 publications

References 39 publications

An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst**

An Aqueous Redox Flow Battery Using CO2 as an Active Material with a Homogeneous Ir Catalyst**

Novel aqueous flow battery using CO2 redox with a bifunctional homogeneous Ir catalyst

Infrared Spectroscopic Observation of Oxo- and Superoxo-Intermediates in the Water Oxidation Cycle of a Molecular Ir Catalyst

Contact Info

Product

Resources

About

An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**

An Aqueous Redox Flow Battery Using CO₂ as an Active Material with a Homogeneous Ir Catalyst**