碱性介质中甘氨酸在Pt电极上解离吸附和氧化反应的原位红外反射光谱研究

运用原位红外反射光谱研究了碱性介质中甘氨酸在Pt电极上的解离吸附和氧化反应行为,并利用纳米Pt膜电极的异常红外效应鉴定反应过程中生成的表面吸附物种.结果表明:甘氨酸在Pt电极上极易发生解离,生成强吸附于电极表面上的氰基负离子,该吸附物种在低于0V电位下能稳定存在,并抑制甘氨酸的进一步反应.当电位高于0.2V时,氰基负离子被氧化为氰酸根离子进入溶液,使甘氨酸发生氧化反应,生成氰酸盐和碳酸盐等产物.

In situ FTIR Spectroscopic Investigations of Dissociative Adsorption and Electrooxidation of Glycine at the Pt Electrode in Alkaline Solutions

The dissociative adsorption and electrooxidation of glycine on Pt electrode in 0.1 mol/L NaOH solutions were studied using cyclic voltammetry and in situ FTIR spectroscopy. The results demonstrated that a strong interaction exists between glycine and Pt surface, leading to dissociate easily glycine on Pt surface at potentials below 0.2 V to form cyanide and carboxylate ions. The strongly adsorbed cyanide species on the electrode surface can inhibit the oxidation of glycine, and are considered as poison species for the reaction. The oxidation of glycine at potentials above 0.2 V yielded solution species of cyanate and carboxylate. The cyanide species derived from dissociative adsorption of glycine can be isolated on electrodes of smooth Pt and nanometer thin Pt film supported on glassy carbon(nm Pt/GC), and has been determined by in situ FTIRS as showing a band at around 2 100 cm -1 . The intensity of IR absorption band of cyanide on nm Pt/GC surface is 14 times larger than that on a smooth Pt surface, and the IR band is in the opposite direction to that obtained on Pt surface, confirming the adsorption of cyanide species and the abnormal IR effects. The IR absorption of cyanate and carboxylate produced in the oxidation of glycine yields infrared bands at around 2 169 and 1 390 cm -1 , respectively. The present study revealed the interaction between glycine and Pt electrode surface, and suggested the adsorption modes and oxidation mechanism of glycine on Pt electrode as well.