Adsorption and precipitation during the redox transformations of phenazine
Adsorption and precipitation during the redox transformations of phenazine
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DOI：
10.1016/j.electacta.2003.12.027
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发表时间：
2004-05
影响因子：
6.6
通讯作者：
G. Inzelt;Z. Puskás
中科院分区：
文献类型：
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作者：
G. Inzelt;Z. Puskás
通过循环和电位阶跃电化学石英晶体微天平测量，研究了酸性水溶液中吩嗪 (Ph) 在金电极上的电化学转化过程中发生的吸附/解吸和沉积/溶解现象。吩嗪在酸性介质中表现出两个连续的单电子还原步骤。在稀吩嗪溶液中，第一次电子转移的产物是吩嗪鎓阳离子自由基（PhH2+̇），它以吩嗪鎓盐（PhH2+̇ClO4−、PhH2+̇Cl−）的形式吸附在电极表面。高氯酸盐高度可溶，电还原通过松散吸附状态发生。在含氯化物的溶液中，观察到多层吸附。稀吩嗪溶液中的第二次电子转移导致 HClO4 中形成 5,10-二氢吩嗪 (PhH2)，并从电极表面解吸。在 HCl 溶液中，大部分完全还原的产物（带电二聚体）保留在表面上。在第二还原波的电位区域中更浓的吩嗪溶液中，可以观察到沉积过程，这是由于醌氢醌类似物吩嗪三酮电荷转移络合物的形成。电荷转移复合物的形成遵循二级动力学，然而，薄膜生长速率受到同时溶解过程的影响。酸浓度的增加促进溶解，并可能阻止成膜。在稀吩嗪溶液中，两个氧化还原波都是可逆的，吸附/解吸过程也是可逆的。在浓溶液中，吩嗪三酮膜的再氧化会导致与溶解-再沉积-溶解顺序相关的复杂伏安响应。
The adsorption/desorption and deposition/dissolution phenomena occurring during the electrochemical transformations of phenazine (Ph) at a gold electrode in aqueous acidic solutions have been studied by cyclic and potential step electrochemical quartz crystal microbalance measurements. Phenazine exhibits two successive one-electron reduction steps in acidic media. In dilute phenazine solutions, the product of the first electron transfer is phenazylium cation radical (PhH2+ ̇) which adsorbs in the form of a phenazylium salt (PhH2+ ̇ClO4−, PhH2+ ̇Cl−) at the electrode surface. The perchlorate salt is highly soluble and the electroreduction takes place via a loosely adsorbed state. In chloride containing solutions, multilayer adsorption is observed. The second electron transfer in dilute phenazine solutions results in the formation of 5,10-dihydrophenazine (PhH2) in HClO4, which desorbs from the electrode surface. In HCl solutions, a substantial portion of the fully reduced product, which is a charged dimer, remains on the surface. In more concentrated phenazine solutions in the potential region of the second reduction wave, a deposition process can be observed, which is due to the formation of the quinhydrone-analogue, phenazinehydrine charge-transfer complex. The formation of the charge-transfer complex obeys a second-order kinetics, however, the rate of the film growth is influenced by the simultaneous dissolution process. The increase of the acid concentration enhances the dissolution, and may prevent the film formation. In dilute phenazine solutions, both redox waves are reversible and likewise the adsorption/desorption processes. In concentrated solutions, the reoxidation of the phenazinehydrine film results in a complicated voltammetric response related to a dissolution–redeposition–dissolution sequence.