In Situ Attenuated Total Reflection Infrared Spectroscopy on Electrochemical Ammonia Oxidation over Pt Electrode in Alkaline Aqueous Solutions

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• 作者：Toshiaki Matsui ; Shohei Suzuki ; Yu Katayama ; Kosuke Yamauchi ; Takeou Okanishi ; Hiroki Muroyama ; Koichi Eguchi
• 刊名：Langmuir
• 出版年：2015
• 出版时间：October 27, 2015
• 年：2015
• 卷：31
• 期：42
• 页码：11717-11723
• 全文大小：540K
• ISSN：1520-5827

文摘

The electrochemical oxidation of ammonia over Pt electrode in alkaline aqueous solutions was studied by in situ attenuated total reflection infrared (ATR-IR) spectroscopy. In 0.1 M NH₃鈥? M KOH, the band ascribable to the HNH bending mode of adsorbed NH₃ was confirmed at 1662鈥?674 cm^鈥? in the potential range of 0.1鈥?.1 V. The intensity of this band decreased continuously with a rise in potential, indicating the oxidative consumption of adsorbed ammonia. In response to this behavior, the band at 1269 cm^鈥? appeared alternatively above 0.2 V, and its intensity reached the local maximal value at ca. 0.4 V. Note that this potential of ca. 0.4 V agreed well with the onset potential of ammonia oxidation, ca. 0.45 V, in the linear sweep voltammogram. This 1269 cm^鈥? band was assigned to the NH₂ wagging mode of N₂H₄, which was one of the active intermediates, N₂H_x+y,ad (x = 1 or 2, y = 1 or 2), according to the mechanism proposed by Gerischer and Mauere. To the best of our knowledge, this is the first report for the detection of N₂H₄ as a reaction intermediate over Pt electrode. Furthermore, the formation of bridged NO was also observed above the onset potential of ammonia oxidation, ca. 0.5 V. Such adsorbed NO species probably inhibit the electrochemical reaction due to the occupation of reaction sites at higher potential.