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

Journal Article · · Inorganic Chemistry
 [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
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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.

Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0001011
OSTI ID:
1225819
Alternate ID(s):
OSTI ID: 1387454
Journal Information:
Inorganic Chemistry, Journal Name: Inorganic Chemistry Vol. 55 Journal Issue: 2; ISSN 0020-1669
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 11 works
Citation information provided by
Web of Science

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Figures / Tables (13)

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Related Subjects

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)