Cu(II) Aliphatic Diamine Complexes for Both Heterogeneous and Homogeneous Water Oxidation Catalysis in Basic and Neutral Solutions

Cui Lu, Jialei Du, Xiao Jun Su, Ming Tian Zhang, Xiaoxiang Xu, Thomas J. Meyer, Zuofeng Chen

Research output: Contribution to journalArticle

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Abstract

Simply mixing a Cu(II) salt and 1,2-ethylenediamine (en) affords precursors for both heterogeneous or homogeneous water oxidation catalysis, depending on pH. In phosphate buffer at pH 12, the Cu(II) en complex formed in solution is decomposed to give a phosphate-incorporated CuO/Cu(OH)2 film on oxide electrodes that catalyzes water oxidation. A current density of 1 mA/cm2 was obtained at an overpotential of 540 mV, a significant enhancement compared to other Cu-based surface catalysts. The results of electrolysis studies suggest that the solution en complex decomposes by en oxidation to glyoxal, following Cu(II) oxidation to Cu(III). At pH 8, the catalysis shifts from heterogeneous to homogeneous with a single-site mechanism for Cu(II)/en complexes in solution. A further decrease in pH to 7 leads to electrode passivation via the formation of a Cu(II) phosphate film during electrolyses. As the pH is decreased, en, with pKb ≈ 6.7, becomes less coordinating and the precipitation of the Cu(II) film inhibits water oxidation. The Cu(II)-based reactivity toward water oxidation is shared by Cu(II) complexation to the analogous 1,3-propylenediamine (pn) ligand over a wide pH range.

LanguageEnglish (US)
Pages77-83
Number of pages7
JournalACS Catalysis
Volume6
Issue number1
DOIs
StatePublished - Jan 4 2016

Fingerprint

ethylenediamine
Diamines
Catalysis
Oxidation
Water
Phosphates
Electrolysis
Glyoxal
Electrodes
Complexation
Passivation
Oxides
Buffers
Current density
Salts
Ligands

Keywords

  • copper
  • heterogeneous catalysis
  • homogeneous catalysis
  • ligand dissociation
  • water oxidation

ASJC Scopus subject areas

  • Catalysis

Cite this

Cu(II) Aliphatic Diamine Complexes for Both Heterogeneous and Homogeneous Water Oxidation Catalysis in Basic and Neutral Solutions. / Lu, Cui; Du, Jialei; Su, Xiao Jun; Zhang, Ming Tian; Xu, Xiaoxiang; Meyer, Thomas J.; Chen, Zuofeng.

In: ACS Catalysis, Vol. 6, No. 1, 04.01.2016, p. 77-83.

Research output: Contribution to journalArticle

Lu, Cui ; Du, Jialei ; Su, Xiao Jun ; Zhang, Ming Tian ; Xu, Xiaoxiang ; Meyer, Thomas J. ; Chen, Zuofeng. / Cu(II) Aliphatic Diamine Complexes for Both Heterogeneous and Homogeneous Water Oxidation Catalysis in Basic and Neutral Solutions. In: ACS Catalysis. 2016 ; Vol. 6, No. 1. pp. 77-83
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abstract = "Simply mixing a Cu(II) salt and 1,2-ethylenediamine (en) affords precursors for both heterogeneous or homogeneous water oxidation catalysis, depending on pH. In phosphate buffer at pH 12, the Cu(II) en complex formed in solution is decomposed to give a phosphate-incorporated CuO/Cu(OH)2 film on oxide electrodes that catalyzes water oxidation. A current density of 1 mA/cm2 was obtained at an overpotential of 540 mV, a significant enhancement compared to other Cu-based surface catalysts. The results of electrolysis studies suggest that the solution en complex decomposes by en oxidation to glyoxal, following Cu(II) oxidation to Cu(III). At pH 8, the catalysis shifts from heterogeneous to homogeneous with a single-site mechanism for Cu(II)/en complexes in solution. A further decrease in pH to 7 leads to electrode passivation via the formation of a Cu(II) phosphate film during electrolyses. As the pH is decreased, en, with pKb ≈ 6.7, becomes less coordinating and the precipitation of the Cu(II) film inhibits water oxidation. The Cu(II)-based reactivity toward water oxidation is shared by Cu(II) complexation to the analogous 1,3-propylenediamine (pn) ligand over a wide pH range.",
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AU - Xu,Xiaoxiang

AU - Meyer,Thomas J.

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N2 - Simply mixing a Cu(II) salt and 1,2-ethylenediamine (en) affords precursors for both heterogeneous or homogeneous water oxidation catalysis, depending on pH. In phosphate buffer at pH 12, the Cu(II) en complex formed in solution is decomposed to give a phosphate-incorporated CuO/Cu(OH)2 film on oxide electrodes that catalyzes water oxidation. A current density of 1 mA/cm2 was obtained at an overpotential of 540 mV, a significant enhancement compared to other Cu-based surface catalysts. The results of electrolysis studies suggest that the solution en complex decomposes by en oxidation to glyoxal, following Cu(II) oxidation to Cu(III). At pH 8, the catalysis shifts from heterogeneous to homogeneous with a single-site mechanism for Cu(II)/en complexes in solution. A further decrease in pH to 7 leads to electrode passivation via the formation of a Cu(II) phosphate film during electrolyses. As the pH is decreased, en, with pKb ≈ 6.7, becomes less coordinating and the precipitation of the Cu(II) film inhibits water oxidation. The Cu(II)-based reactivity toward water oxidation is shared by Cu(II) complexation to the analogous 1,3-propylenediamine (pn) ligand over a wide pH range.

AB - Simply mixing a Cu(II) salt and 1,2-ethylenediamine (en) affords precursors for both heterogeneous or homogeneous water oxidation catalysis, depending on pH. In phosphate buffer at pH 12, the Cu(II) en complex formed in solution is decomposed to give a phosphate-incorporated CuO/Cu(OH)2 film on oxide electrodes that catalyzes water oxidation. A current density of 1 mA/cm2 was obtained at an overpotential of 540 mV, a significant enhancement compared to other Cu-based surface catalysts. The results of electrolysis studies suggest that the solution en complex decomposes by en oxidation to glyoxal, following Cu(II) oxidation to Cu(III). At pH 8, the catalysis shifts from heterogeneous to homogeneous with a single-site mechanism for Cu(II)/en complexes in solution. A further decrease in pH to 7 leads to electrode passivation via the formation of a Cu(II) phosphate film during electrolyses. As the pH is decreased, en, with pKb ≈ 6.7, becomes less coordinating and the precipitation of the Cu(II) film inhibits water oxidation. The Cu(II)-based reactivity toward water oxidation is shared by Cu(II) complexation to the analogous 1,3-propylenediamine (pn) ligand over a wide pH range.

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