Journal
JOURNAL OF THE AMERICAN CHEMICAL SOCIETY
Volume 136, Issue 18, Pages 6744-6753Publisher
AMER CHEMICAL SOC
DOI: 10.1021/ja502379c
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Funding
- National Science Foundation [CHE-1301461]
- W. M. Keck Foundation
- M. J. Murdock Charitable Trust
- ONAMI
- Air Force Research Laboratory [FA8650-05-1-5041]
- NSF [236200]
- University of Oregon
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1301461] Funding Source: National Science Foundation
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Fe plays a critical, but not yet understood, role in enhancing the activity of the Ni-based oxygen evolution reaction (OER) electrocatalysts. We report electrochemical, in situ electrical, photoelectron spectroscopy, and X-ray diffraction measurements on Ni1-xFex(OH)(2)/Ni1-xFexOOH thin films to investigate the changes in electronic properties, OER activity, and structure as a result of Fe inclusion. We developed a simple method for purification of KOH electrolyte that uses precipitated bulk Ni(OH)(2) to absorb Fe impurities. Cyclic voltammetry on rigorously Fe-free Ni(OH)(2)/NiOOH reveals new Ni redox features and no significant OER current until >400 mV overpotential, different from previous reports which were likely affected by Fe impurities. We show through controlled crystallization that beta-NiOOH is less active for OER than the disordered gamma-NiOOH starting material and that previous reports of increased activity for beta-NiOOH are due to incorporation of Fe-impurities during the crystallization process. Through-film in situ conductivity measurements show a >30-fold increase in film conductivity with Fe addition, but this change in conductivity is not sufficient to explain the observed changes in activity. Measurements of activity as a function of film thickness on Au and glassy carbon substrates are consistent with the hypothesis that Fe exerts a partial-charge-transfer activation effect on Ni, similar to that observed for noble-metal electrode surfaces. These results have significant implications for the design and study of Ni1-xFexOOH OER electrocatalysts, which are the fastest measured OER catalysts under basic conditions.
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