Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 132, Issue 46, Pages 16501-16509Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja106102b
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Funding
- Center for Chemical Innovation of the National Science Foundation [CHE-0802907, CHE-0947829]
- AFOSR [FA9550-09-1-0689]
- Chesonis Family Foundation
- National Science Foundation
- NIH
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [0802907] Funding Source: National Science Foundation
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The mechanism of the oxygen evolution reaction (OER) by catalysts prepared by electrodepositions from Co2+ solutions in phosphate electrolytes (Co-Pi) was studied at neutral pH by electrokinetic and O-18 isotope experiments. Low-potential electrodepositions enabled the controlled preparation of ultrathin Co-Pi catalyst films (<100 nm) that could be studied kinetically in the absence of mass transport and charge transport limitations to the OER. The Co-Pi catalysts exhibit a Tafel slope approximately equal to 2.3 x RT/F for the production of oxygen from water in neutral solutions. The electrochemical rate law exhibits an inverse first order dependence on proton activity and a zeroth order dependence on phosphate for [Pi] >= 0.03 M. In the absence of phosphate buffer, the Tafel slope is increased similar to 3-fold and the overall activity is greatly diminished. Together, these electrokinetic studies suggest a mechanism involving a rapid, one electron, one proton equilibrium between Co-III-OH and Co-IV-O in which a phosphate species is the proton acceptor, followed by a chemical turnover-limiting process involving oxygen-oxygen bond coupling.
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