Nickel鈥揑ron Oxyhydroxide Oxygen-Evolution Electrocatalysts: The Role of Intentional and Incidental Iron Incorporation
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- 作者：Lena Trotochaud ; Samantha L. Young ; James K. Ranney ; Shannon W. Boettcher
- 刊名：Journal of the American Chemical Society
- 出版年：2014
- 出版时间：May 7, 2014
- 年：2014
- 卷：136
- 期：18
- 页码：6744-6753
- 全文大小：577K
- 年卷期：v.136,no.18(May 7, 2014)
- ISSN：1520-5126
文摘
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鈥?i>xFex(OH)2/Ni1鈥?i>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 尾-NiOOH is less active for OER than the disordered 纬-NiOOH starting material and that previous reports of increased activity for 尾-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鈥?i>xFexOOH OER electrocatalysts, which are the fastest measured OER catalysts under basic conditions.