Electrochemical Detection of Transient Cobalt Hydride Intermediates of Electrocatalytic Hydrogen Production

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Abstract

A large variety of molecular cobalt complexes are used as electrocatalysts for H2 production, but the key cobalt hydride intermediates are frequently difficult to detect and characterize due to their high reactivity. We report that a combination of variable scan rate cyclic voltammetry and foot-of-the-wave analysis (FOWA) can be used to detect transient CoIIIH and CoIIH intermediates of electrocatalytic H2 production by [CoII(PtBu 2NPh 2)(CH3CN)3]2+ and CoII(dmgBF2)2(CH3CN)2. In both cases, reduction of a transient catalytic intermediate occurs at a potential that coincides with the CoII/I couple. Each reduction displays quasireversible electron-transfer kinetics, consistent with reduction of a CoIIIH intermediate to CoIIH, which is then protonated by acid to generate H2. A bridge-protonated CoI species was ruled out as a catalytic intermediate for CoII(dmgBF2)2(CH3CN)2 from voltammograms recorded at 1000 psi of H2. Density functional theory was used to calculate CoIII-H and CoII-H bond strengths for both catalysts. Despite having very different ligands, the cobalt hydrides of both catalysts possess nearly identical heterolytic and homolytic Co-H bond strengths for the CoIIIH and CoIIH intermediates.

Original languageEnglish
Pages (from-to)8309-8318
Number of pages10
JournalJournal of the American Chemical Society
Volume138
Issue number26
DOIs
Publication statusPublished - Jul 6 2016

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Hydrogen production
Cobalt
Hydrides
Hydrogen
Catalysts
Electrocatalysts
Cyclic voltammetry
Density functional theory
Foot
Ligands
Electrons
Kinetics
Acids

ASJC Scopus subject areas

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

Cite this

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title = "Electrochemical Detection of Transient Cobalt Hydride Intermediates of Electrocatalytic Hydrogen Production",
abstract = "A large variety of molecular cobalt complexes are used as electrocatalysts for H2 production, but the key cobalt hydride intermediates are frequently difficult to detect and characterize due to their high reactivity. We report that a combination of variable scan rate cyclic voltammetry and foot-of-the-wave analysis (FOWA) can be used to detect transient CoIIIH and CoIIH intermediates of electrocatalytic H2 production by [CoII(PtBu 2NPh 2)(CH3CN)3]2+ and CoII(dmgBF2)2(CH3CN)2. In both cases, reduction of a transient catalytic intermediate occurs at a potential that coincides with the CoII/I couple. Each reduction displays quasireversible electron-transfer kinetics, consistent with reduction of a CoIIIH intermediate to CoIIH, which is then protonated by acid to generate H2. A bridge-protonated CoI species was ruled out as a catalytic intermediate for CoII(dmgBF2)2(CH3CN)2 from voltammograms recorded at 1000 psi of H2. Density functional theory was used to calculate CoIII-H and CoII-H bond strengths for both catalysts. Despite having very different ligands, the cobalt hydrides of both catalysts possess nearly identical heterolytic and homolytic Co-H bond strengths for the CoIIIH and CoIIH intermediates.",
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T1 - Electrochemical Detection of Transient Cobalt Hydride Intermediates of Electrocatalytic Hydrogen Production

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N2 - A large variety of molecular cobalt complexes are used as electrocatalysts for H2 production, but the key cobalt hydride intermediates are frequently difficult to detect and characterize due to their high reactivity. We report that a combination of variable scan rate cyclic voltammetry and foot-of-the-wave analysis (FOWA) can be used to detect transient CoIIIH and CoIIH intermediates of electrocatalytic H2 production by [CoII(PtBu 2NPh 2)(CH3CN)3]2+ and CoII(dmgBF2)2(CH3CN)2. In both cases, reduction of a transient catalytic intermediate occurs at a potential that coincides with the CoII/I couple. Each reduction displays quasireversible electron-transfer kinetics, consistent with reduction of a CoIIIH intermediate to CoIIH, which is then protonated by acid to generate H2. A bridge-protonated CoI species was ruled out as a catalytic intermediate for CoII(dmgBF2)2(CH3CN)2 from voltammograms recorded at 1000 psi of H2. Density functional theory was used to calculate CoIII-H and CoII-H bond strengths for both catalysts. Despite having very different ligands, the cobalt hydrides of both catalysts possess nearly identical heterolytic and homolytic Co-H bond strengths for the CoIIIH and CoIIH intermediates.

AB - A large variety of molecular cobalt complexes are used as electrocatalysts for H2 production, but the key cobalt hydride intermediates are frequently difficult to detect and characterize due to their high reactivity. We report that a combination of variable scan rate cyclic voltammetry and foot-of-the-wave analysis (FOWA) can be used to detect transient CoIIIH and CoIIH intermediates of electrocatalytic H2 production by [CoII(PtBu 2NPh 2)(CH3CN)3]2+ and CoII(dmgBF2)2(CH3CN)2. In both cases, reduction of a transient catalytic intermediate occurs at a potential that coincides with the CoII/I couple. Each reduction displays quasireversible electron-transfer kinetics, consistent with reduction of a CoIIIH intermediate to CoIIH, which is then protonated by acid to generate H2. A bridge-protonated CoI species was ruled out as a catalytic intermediate for CoII(dmgBF2)2(CH3CN)2 from voltammograms recorded at 1000 psi of H2. Density functional theory was used to calculate CoIII-H and CoII-H bond strengths for both catalysts. Despite having very different ligands, the cobalt hydrides of both catalysts possess nearly identical heterolytic and homolytic Co-H bond strengths for the CoIIIH and CoIIH intermediates.

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