Water oxidation catalysis by nanoparticulate manganese oxide thin films: Probing the effect of the manganese precursors

Archana Singh, Rosalie K. Hocking, Lan-Yun Chang, Benjamin M. George, Matthias Fehr, Klaus Lips, Alexander Schnegg, Leone Spiccia

Research output: Contribution to journalArticle

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Abstract

Nanoparticulate manganese oxides, formed in Nafion polymer from a series of molecular manganese complexes of varying nuclearity and metal oxidation state, are shown to effectively catalyze water oxidation under neutral pH conditions with the onset of electrocatalysis occurring at an overpotential of only 150 mV. Although XAS experiments indicate that each complex generates the same material in Nafion, the catalytic activity varied substantially with the manganese precursor and did not correlate with the amount of MnOx present in the films. The XAS and EPR studies indicated that the formation of the nanoparticulate oxide involves the dissociation of the complex into Mn(II) species followed by oxidation on application of an external bias. TEM studies of the most active films, derived from [Mn(Me3TACN)(OMe) 3]+ and [(Me3TACN)2Mn III 2(μ-O)(μ-CH3COO)2] 2+ (Me3TACN = N,N′,N″-trimethyl-1,4,7- triazacyclononane), revealed that highly dispersed MnOx nanoparticles (10-20 nm and 6-10 nm, respectively) were generated in the Nafion film. In contrast, the use of [Mn(OH2)6]2+ resulted in both a higher manganese oxide loading and aggregated nanoparticles with 30-100 nm approximate size, which were less effective water oxidation catalysts. Much higher turnover frequencies (TOFs) were observed for films derived from the two complexes, viz., ∼20 molecules of O2 per Mn per hour in dark and 40 molecules of O2 per Mn per hour under illumination at an overpotential of 350 mV, when compared with MnOx films made with [Mn(OH2)6]2+. This corresponds to a TOF > 100 molecules of O2 per Mn per second for a 10 nm MnOx nanoparticle. Thus, the catalytic activity is dependent on the ability to generate well-defined, dispersed nanoparticles. Electrochemical and spectroscopic methods have been used to follow the conversion of the molecular precursors into MnOx and to further evaluate the origin of differences in catalytic activity.

Original languageEnglish (US)
Pages (from-to)1098-1108
Number of pages11
JournalChemistry of Materials
Volume25
Issue number7
DOIs
StatePublished - Apr 9 2013
Externally publishedYes

Fingerprint

Manganese oxide
Manganese
Catalysis
Oxide films
Thin films
Oxidation
Water
Nanoparticles
Catalyst activity
Molecules
Electrocatalysis
Oxides
Paramagnetic resonance
Polymers
Lighting
Metals
manganese oxide
Transmission electron microscopy
Catalysts
perfluorosulfonic acid

Keywords

  • electrodeposition
  • EPR spectroscopy
  • manganese complexes
  • nanoparticulate manganese oxides
  • transmission electron microscopy
  • water oxidation catalysis
  • X-ray absorption spectroscopy

ASJC Scopus subject areas

  • Chemistry(all)
  • Chemical Engineering(all)
  • Materials Chemistry

Cite this

Water oxidation catalysis by nanoparticulate manganese oxide thin films : Probing the effect of the manganese precursors. / Singh, Archana; Hocking, Rosalie K.; Chang, Lan-Yun; George, Benjamin M.; Fehr, Matthias; Lips, Klaus; Schnegg, Alexander; Spiccia, Leone.

In: Chemistry of Materials, Vol. 25, No. 7, 09.04.2013, p. 1098-1108.

Research output: Contribution to journalArticle

Singh, Archana ; Hocking, Rosalie K. ; Chang, Lan-Yun ; George, Benjamin M. ; Fehr, Matthias ; Lips, Klaus ; Schnegg, Alexander ; Spiccia, Leone. / Water oxidation catalysis by nanoparticulate manganese oxide thin films : Probing the effect of the manganese precursors. In: Chemistry of Materials. 2013 ; Vol. 25, No. 7. pp. 1098-1108.
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abstract = "Nanoparticulate manganese oxides, formed in Nafion polymer from a series of molecular manganese complexes of varying nuclearity and metal oxidation state, are shown to effectively catalyze water oxidation under neutral pH conditions with the onset of electrocatalysis occurring at an overpotential of only 150 mV. Although XAS experiments indicate that each complex generates the same material in Nafion, the catalytic activity varied substantially with the manganese precursor and did not correlate with the amount of MnOx present in the films. The XAS and EPR studies indicated that the formation of the nanoparticulate oxide involves the dissociation of the complex into Mn(II) species followed by oxidation on application of an external bias. TEM studies of the most active films, derived from [Mn(Me3TACN)(OMe) 3]+ and [(Me3TACN)2Mn III 2(μ-O)(μ-CH3COO)2] 2+ (Me3TACN = N,N′,N″-trimethyl-1,4,7- triazacyclononane), revealed that highly dispersed MnOx nanoparticles (10-20 nm and 6-10 nm, respectively) were generated in the Nafion film. In contrast, the use of [Mn(OH2)6]2+ resulted in both a higher manganese oxide loading and aggregated nanoparticles with 30-100 nm approximate size, which were less effective water oxidation catalysts. Much higher turnover frequencies (TOFs) were observed for films derived from the two complexes, viz., ∼20 molecules of O2 per Mn per hour in dark and 40 molecules of O2 per Mn per hour under illumination at an overpotential of 350 mV, when compared with MnOx films made with [Mn(OH2)6]2+. This corresponds to a TOF > 100 molecules of O2 per Mn per second for a 10 nm MnOx nanoparticle. Thus, the catalytic activity is dependent on the ability to generate well-defined, dispersed nanoparticles. Electrochemical and spectroscopic methods have been used to follow the conversion of the molecular precursors into MnOx and to further evaluate the origin of differences in catalytic activity.",
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AU - Chang, Lan-Yun

AU - George, Benjamin M.

AU - Fehr, Matthias

AU - Lips, Klaus

AU - Schnegg, Alexander

AU - Spiccia, Leone

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N2 - Nanoparticulate manganese oxides, formed in Nafion polymer from a series of molecular manganese complexes of varying nuclearity and metal oxidation state, are shown to effectively catalyze water oxidation under neutral pH conditions with the onset of electrocatalysis occurring at an overpotential of only 150 mV. Although XAS experiments indicate that each complex generates the same material in Nafion, the catalytic activity varied substantially with the manganese precursor and did not correlate with the amount of MnOx present in the films. The XAS and EPR studies indicated that the formation of the nanoparticulate oxide involves the dissociation of the complex into Mn(II) species followed by oxidation on application of an external bias. TEM studies of the most active films, derived from [Mn(Me3TACN)(OMe) 3]+ and [(Me3TACN)2Mn III 2(μ-O)(μ-CH3COO)2] 2+ (Me3TACN = N,N′,N″-trimethyl-1,4,7- triazacyclononane), revealed that highly dispersed MnOx nanoparticles (10-20 nm and 6-10 nm, respectively) were generated in the Nafion film. In contrast, the use of [Mn(OH2)6]2+ resulted in both a higher manganese oxide loading and aggregated nanoparticles with 30-100 nm approximate size, which were less effective water oxidation catalysts. Much higher turnover frequencies (TOFs) were observed for films derived from the two complexes, viz., ∼20 molecules of O2 per Mn per hour in dark and 40 molecules of O2 per Mn per hour under illumination at an overpotential of 350 mV, when compared with MnOx films made with [Mn(OH2)6]2+. This corresponds to a TOF > 100 molecules of O2 per Mn per second for a 10 nm MnOx nanoparticle. Thus, the catalytic activity is dependent on the ability to generate well-defined, dispersed nanoparticles. Electrochemical and spectroscopic methods have been used to follow the conversion of the molecular precursors into MnOx and to further evaluate the origin of differences in catalytic activity.

AB - Nanoparticulate manganese oxides, formed in Nafion polymer from a series of molecular manganese complexes of varying nuclearity and metal oxidation state, are shown to effectively catalyze water oxidation under neutral pH conditions with the onset of electrocatalysis occurring at an overpotential of only 150 mV. Although XAS experiments indicate that each complex generates the same material in Nafion, the catalytic activity varied substantially with the manganese precursor and did not correlate with the amount of MnOx present in the films. The XAS and EPR studies indicated that the formation of the nanoparticulate oxide involves the dissociation of the complex into Mn(II) species followed by oxidation on application of an external bias. TEM studies of the most active films, derived from [Mn(Me3TACN)(OMe) 3]+ and [(Me3TACN)2Mn III 2(μ-O)(μ-CH3COO)2] 2+ (Me3TACN = N,N′,N″-trimethyl-1,4,7- triazacyclononane), revealed that highly dispersed MnOx nanoparticles (10-20 nm and 6-10 nm, respectively) were generated in the Nafion film. In contrast, the use of [Mn(OH2)6]2+ resulted in both a higher manganese oxide loading and aggregated nanoparticles with 30-100 nm approximate size, which were less effective water oxidation catalysts. Much higher turnover frequencies (TOFs) were observed for films derived from the two complexes, viz., ∼20 molecules of O2 per Mn per hour in dark and 40 molecules of O2 per Mn per hour under illumination at an overpotential of 350 mV, when compared with MnOx films made with [Mn(OH2)6]2+. This corresponds to a TOF > 100 molecules of O2 per Mn per second for a 10 nm MnOx nanoparticle. Thus, the catalytic activity is dependent on the ability to generate well-defined, dispersed nanoparticles. Electrochemical and spectroscopic methods have been used to follow the conversion of the molecular precursors into MnOx and to further evaluate the origin of differences in catalytic activity.

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KW - EPR spectroscopy

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KW - transmission electron microscopy

KW - water oxidation catalysis

KW - X-ray absorption spectroscopy

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