Direct Observation of C2O4 •- and CO2 •- by Oxidation of Oxalate within Nanogap of Scanning Electrochemical Microscope

Tianhan Kai, Min Zhou, Sarah Johnson, Hyun S. Ahn, Allen J. Bard

Research output: Contribution to journalArticle

3 Citations (Scopus)

Abstract

Oxalate oxidation in the presence of different oxidized luminophores leads to the emission of light and has been studied extensively in electrogenerated chemiluminescence (ECL). The proposed mechanism involves the initial formation of the oxalate radical anion, C2O4 •-. The ensuing decomposition of C2O4 •- produces a very strong reductant, CO2 •-, which reacts with the oxidized luminophores to generate excited states that emit light. Although the mechanism has been proposed for decades, the experimental demonstration is still lacking, because of the complexity of the system and the short lifetimes of both radical anions. To address these issues, we studied oxalate oxidation at platinum ultramicroelectrodes (UMEs) in anhydrous N,N-dimethylformamide (DMF) solution by nanoscale scanning electrochemical microscopy (SECM) with the tip generation/substrate collection (TG/SC) mode. A Pt nanoelectrode was utilized as the SECM generator for oxalate oxidation, while another Pt UME served as the SECM collector and was used to capture the generated intermediates. We studied the influence of the gap distance, d, on the substrate current (is). The results indicate that, when 73 nm < d < 500 nm, the species captured by the substrate were primarily CO2 •-, while C2O4 •- was the predominant intermediate measured when d was below 73 nm. A half-life of 1.3 μs for C2O4 •- was obtained, which indicates a stepwise mechanism for oxalate oxidation. The relevance of these observations to the use of oxalate as the coreactant in ECL systems is also discussed.

Original languageEnglish
Pages (from-to)16178-16183
Number of pages6
JournalJournal of the American Chemical Society
Volume140
Issue number47
DOIs
Publication statusPublished - 2018 Nov 28

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Oxalates
Electrochemical Scanning Microscopy
Microscopes
Observation
Scanning
Oxidation
Microscopic examination
Chemiluminescence
Substrates
Negative ions
Luminescence
Anions
Dimethylformamide
Excited states
Light
Platinum
Demonstrations
Reducing Agents
Decomposition
Half-Life

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

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abstract = "Oxalate oxidation in the presence of different oxidized luminophores leads to the emission of light and has been studied extensively in electrogenerated chemiluminescence (ECL). The proposed mechanism involves the initial formation of the oxalate radical anion, C2O4 •-. The ensuing decomposition of C2O4 •- produces a very strong reductant, CO2 •-, which reacts with the oxidized luminophores to generate excited states that emit light. Although the mechanism has been proposed for decades, the experimental demonstration is still lacking, because of the complexity of the system and the short lifetimes of both radical anions. To address these issues, we studied oxalate oxidation at platinum ultramicroelectrodes (UMEs) in anhydrous N,N-dimethylformamide (DMF) solution by nanoscale scanning electrochemical microscopy (SECM) with the tip generation/substrate collection (TG/SC) mode. A Pt nanoelectrode was utilized as the SECM generator for oxalate oxidation, while another Pt UME served as the SECM collector and was used to capture the generated intermediates. We studied the influence of the gap distance, d, on the substrate current (is). The results indicate that, when 73 nm < d < 500 nm, the species captured by the substrate were primarily CO2 •-, while C2O4 •- was the predominant intermediate measured when d was below 73 nm. A half-life of 1.3 μs for C2O4 •- was obtained, which indicates a stepwise mechanism for oxalate oxidation. The relevance of these observations to the use of oxalate as the coreactant in ECL systems is also discussed.",
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Direct Observation of C2O4 •- and CO2 •- by Oxidation of Oxalate within Nanogap of Scanning Electrochemical Microscope. / Kai, Tianhan; Zhou, Min; Johnson, Sarah; Ahn, Hyun S.; Bard, Allen J.

In: Journal of the American Chemical Society, Vol. 140, No. 47, 28.11.2018, p. 16178-16183.

Research output: Contribution to journalArticle

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T1 - Direct Observation of C2O4 •- and CO2 •- by Oxidation of Oxalate within Nanogap of Scanning Electrochemical Microscope

AU - Kai, Tianhan

AU - Zhou, Min

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AU - Bard, Allen J.

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N2 - Oxalate oxidation in the presence of different oxidized luminophores leads to the emission of light and has been studied extensively in electrogenerated chemiluminescence (ECL). The proposed mechanism involves the initial formation of the oxalate radical anion, C2O4 •-. The ensuing decomposition of C2O4 •- produces a very strong reductant, CO2 •-, which reacts with the oxidized luminophores to generate excited states that emit light. Although the mechanism has been proposed for decades, the experimental demonstration is still lacking, because of the complexity of the system and the short lifetimes of both radical anions. To address these issues, we studied oxalate oxidation at platinum ultramicroelectrodes (UMEs) in anhydrous N,N-dimethylformamide (DMF) solution by nanoscale scanning electrochemical microscopy (SECM) with the tip generation/substrate collection (TG/SC) mode. A Pt nanoelectrode was utilized as the SECM generator for oxalate oxidation, while another Pt UME served as the SECM collector and was used to capture the generated intermediates. We studied the influence of the gap distance, d, on the substrate current (is). The results indicate that, when 73 nm < d < 500 nm, the species captured by the substrate were primarily CO2 •-, while C2O4 •- was the predominant intermediate measured when d was below 73 nm. A half-life of 1.3 μs for C2O4 •- was obtained, which indicates a stepwise mechanism for oxalate oxidation. The relevance of these observations to the use of oxalate as the coreactant in ECL systems is also discussed.

AB - Oxalate oxidation in the presence of different oxidized luminophores leads to the emission of light and has been studied extensively in electrogenerated chemiluminescence (ECL). The proposed mechanism involves the initial formation of the oxalate radical anion, C2O4 •-. The ensuing decomposition of C2O4 •- produces a very strong reductant, CO2 •-, which reacts with the oxidized luminophores to generate excited states that emit light. Although the mechanism has been proposed for decades, the experimental demonstration is still lacking, because of the complexity of the system and the short lifetimes of both radical anions. To address these issues, we studied oxalate oxidation at platinum ultramicroelectrodes (UMEs) in anhydrous N,N-dimethylformamide (DMF) solution by nanoscale scanning electrochemical microscopy (SECM) with the tip generation/substrate collection (TG/SC) mode. A Pt nanoelectrode was utilized as the SECM generator for oxalate oxidation, while another Pt UME served as the SECM collector and was used to capture the generated intermediates. We studied the influence of the gap distance, d, on the substrate current (is). The results indicate that, when 73 nm < d < 500 nm, the species captured by the substrate were primarily CO2 •-, while C2O4 •- was the predominant intermediate measured when d was below 73 nm. A half-life of 1.3 μs for C2O4 •- was obtained, which indicates a stepwise mechanism for oxalate oxidation. The relevance of these observations to the use of oxalate as the coreactant in ECL systems is also discussed.

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