Speciation of Adsorbed Phosphate at Gold Electrodes: A Combined Surface-Enhanced Infrared Absorption Spectroscopy and DFT Study

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• 作者：Momo Yaguchi ; Taro Uchida ; Kenta Motobayashi ; Masatoshi Osawa
• 刊名：The Journal of Physical Chemistry Letters
• 出版年：2016
• 出版时间：August 18, 2016
• 年：2016
• 卷：7
• 期：16
• 页码：3097-3102
• 全文大小：447K
• 年卷期：0
• ISSN：1948-7185

文摘

Despite the significance of phosphate buffer solutions in (bio)electrochemistry, detailed adsorption properties of phosphate anions at metal surfaces remain poorly understood. Herein, phosphate adsorption at quasi-Au(111) surfaces prepared by a chemical deposition technique has been systematically investigated over a wide range of pH by surface-enhanced infrared absorption spectroscopy in the ATR configuration (ATR-SEIRAS). Two different pH-dependent states of adsorbed phosphate are spectroscopically detected. Together with DFT calculations, the present study reveals that pK_a for adsorbed phosphate species at the interface is much lower than that for phosphate species in the bulk solution; the dominant phosphate anion, H₂PO₄^– at 2 < pH < 7 or HPO₄^2– at 7 < pH < 12, undergoes deprotonation upon adsorption and transforms into the adsorbed HPO₄ or PO₄, respectively. This study leads to a conclusion different than earlier spectroscopic studies have reached, highlighting the capability of the ATR-SEIRAS technique at electrified metal–solution interfaces.