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Title: Analysis of Homogeneous Water Oxidation Catalysis with Collector–Generator Cells

Abstract

A collector–generator (C–G) technique has been applied to determine the Faradaic efficiencies for electrocatalytic O2 production by the homogeneous water oxidation catalysts Ru(bda)(isoq)2 (1; bda = 2,2'-bipyridine and isoq = isoquinoline) and [Ru(tpy)(bpz)(OH2)]2+ (2; tpy = 2,2':6',2"-terpyridine and bpz = 2,2'-bipyrazine). This technique uses a custom-fabricated cell consisting of two fluorine-doped tin oxide (FTO) working electrodes separated by 1 mm with the conductive sides facing each other. With a catalyst in solution, water oxidation occurs at one FTO electrode under a sufficient bias to drive O2 formation by the catalyst; the O2 formed then diffuses to the second FTO electrode poised at a potential sufficiently negative to drive O2 reduction. A comparison of the current versus time response at each electrode enables determination of the Faradaic efficiency for O2 production with high concentrations of supporting electrolyte important for avoiding capacitance effects between the electrodes. The C–G technique was applied to electrocatalytic water oxidation by 1 in the presence of the electron-transfer mediator Ru(bpy)32+ in both unbuffered aqueous solutions and with the added buffer bases HCO3, HPO42–, imidazole, 1-methylimidazole, and 4-methoxypyridine. HCO3 and HPO42– facilitate water oxidation by atom-proton transfer (APT), which gave Faradaic yields of 100%. With imidazole as themore » buffer base, coordination to the catalyst inhibited water oxidation. 1-Methylimidazole and 4-methoxypyridine gave O2 yields of 55% and 76%, respectively, with the lower Faradaic efficiencies possibly due to competitive C–H oxidation of the bases. O2 evolution by catalyst 2 was evaluated at pH 12 with 0.1 M PO43– and at pH 7 in a 0.1 M H2PO4/HPO42– buffer. At pH 12, at an applied potential of 0.8 V vs SCE, water oxidation by the RuIV(O)2+ form of the catalyst gave O2 in 73% yield. In a pH 7 solution, water oxidation at 1.4 V vs SCE, which is dominated by RuV(O)3+, gave O2 with an efficiency of 100%. The lower efficiency for RuIV(O)2+ at pH 12 may be due to competitive oxidation of a polypyridyl ligand.« less

Authors:
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, United States
Publication Date:
Research Org.:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1225819
Alternate Identifier(s):
OSTI ID: 1387454
Grant/Contract Number:  
SC0001011
Resource Type:
Published Article
Journal Name:
Inorganic Chemistry
Additional Journal Information:
Journal Name: Inorganic Chemistry Journal Volume: 55 Journal Issue: 2; Journal ID: ISSN 0020-1669
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; catalysis (homogeneous); catalysis (heterogeneous); solar (photovoltaic); solar (fuels); photosynthesis (natural and artificial); hydrogen and fuel cells; electrodes - solar; charge transport; materials and chemistry by design; synthesis (novel materials); synthesis (self-assembly)

Citation Formats

Sherman, Benjamin D., Sheridan, Matthew V., Wee, Kyung-Ryang, Song, Na, Dares, Christopher J., Fang, Zhen, Tamaki, Yusuke, Nayak, Animesh, and Meyer, Thomas J. Analysis of Homogeneous Water Oxidation Catalysis with Collector–Generator Cells. United States: N. p., 2015. Web. doi:10.1021/acs.inorgchem.5b02182.
Sherman, Benjamin D., Sheridan, Matthew V., Wee, Kyung-Ryang, Song, Na, Dares, Christopher J., Fang, Zhen, Tamaki, Yusuke, Nayak, Animesh, & Meyer, Thomas J. Analysis of Homogeneous Water Oxidation Catalysis with Collector–Generator Cells. United States. doi:10.1021/acs.inorgchem.5b02182.
Sherman, Benjamin D., Sheridan, Matthew V., Wee, Kyung-Ryang, Song, Na, Dares, Christopher J., Fang, Zhen, Tamaki, Yusuke, Nayak, Animesh, and Meyer, Thomas J. Thu . "Analysis of Homogeneous Water Oxidation Catalysis with Collector–Generator Cells". United States. doi:10.1021/acs.inorgchem.5b02182.
@article{osti_1225819,
title = {Analysis of Homogeneous Water Oxidation Catalysis with Collector–Generator Cells},
author = {Sherman, Benjamin D. and Sheridan, Matthew V. and Wee, Kyung-Ryang and Song, Na and Dares, Christopher J. and Fang, Zhen and Tamaki, Yusuke and Nayak, Animesh and Meyer, Thomas J.},
abstractNote = {A collector–generator (C–G) technique has been applied to determine the Faradaic efficiencies for electrocatalytic O2 production by the homogeneous water oxidation catalysts Ru(bda)(isoq)2 (1; bda = 2,2'-bipyridine and isoq = isoquinoline) and [Ru(tpy)(bpz)(OH2)]2+ (2; tpy = 2,2':6',2"-terpyridine and bpz = 2,2'-bipyrazine). This technique uses a custom-fabricated cell consisting of two fluorine-doped tin oxide (FTO) working electrodes separated by 1 mm with the conductive sides facing each other. With a catalyst in solution, water oxidation occurs at one FTO electrode under a sufficient bias to drive O2 formation by the catalyst; the O2 formed then diffuses to the second FTO electrode poised at a potential sufficiently negative to drive O2 reduction. A comparison of the current versus time response at each electrode enables determination of the Faradaic efficiency for O2 production with high concentrations of supporting electrolyte important for avoiding capacitance effects between the electrodes. The C–G technique was applied to electrocatalytic water oxidation by 1 in the presence of the electron-transfer mediator Ru(bpy)32+ in both unbuffered aqueous solutions and with the added buffer bases HCO3–, HPO42–, imidazole, 1-methylimidazole, and 4-methoxypyridine. HCO3– and HPO42– facilitate water oxidation by atom-proton transfer (APT), which gave Faradaic yields of 100%. With imidazole as the buffer base, coordination to the catalyst inhibited water oxidation. 1-Methylimidazole and 4-methoxypyridine gave O2 yields of 55% and 76%, respectively, with the lower Faradaic efficiencies possibly due to competitive C–H oxidation of the bases. O2 evolution by catalyst 2 was evaluated at pH 12 with 0.1 M PO43– and at pH 7 in a 0.1 M H2PO4–/HPO42– buffer. At pH 12, at an applied potential of 0.8 V vs SCE, water oxidation by the RuIV(O)2+ form of the catalyst gave O2 in 73% yield. In a pH 7 solution, water oxidation at 1.4 V vs SCE, which is dominated by RuV(O)3+, gave O2 with an efficiency of 100%. The lower efficiency for RuIV(O)2+ at pH 12 may be due to competitive oxidation of a polypyridyl ligand.},
doi = {10.1021/acs.inorgchem.5b02182},
journal = {Inorganic Chemistry},
number = 2,
volume = 55,
place = {United States},
year = {2015},
month = {11}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record
DOI: 10.1021/acs.inorgchem.5b02182

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Cited by: 8 works
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Figures / Tables:

Figure 1 Figure 1: Schematic diagram of the C−G cell for O2 production and analysis.

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