Scanning electrochemical microscopy: using the potentiometric mode of SECM to study the mixed potential arising from two independent redox processes.
Scanning electrochemical microscopy: using the potentiometric mode of SECM to study the mixed potential arising from two independent redox processes.
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DOI：
10.1021/ac4017055
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发表时间：
2013-08
影响因子：
7.4
通讯作者：
M. Serrapede;G. Denuault;M. Sosna;G. Pesce;R. Ball
中科院分区：
文献类型：
--
作者：
M. Serrapede;G. Denuault;M. Sosna;G. Pesce;R. Ball
这项研究演示了如何电位模式的扫描电化学显微镜（SECM）可以用来灵敏地探测和改变混合电位由于两个独立的氧化还原过程，所涉及的物种之一的运输是由扩散控制。这是说明与放电的氢从纳米结构的Pd氢化物薄膜上沉积的SECM尖端。在脱气缓冲溶液中，PdH处于β-α相平衡时的开路电位（OCP（β→α））不依赖于针尖-基体距离，而在充气条件下，它受氧扩散受阻的控制。计时电位和安培测量在几个尖端基板的距离揭示了如何向钯氢化物膜的氧通量决定其电位。线性扫描伏安法表明，当针尖接近惰性基底时，极化电阻增加。SECM方法还演示了溶解氧如何影响从Pd晶格中提取氢的速率。在宽的电势窗口上，高反应性纳米结构促进氧的还原，这快速地从PdH释放氢。朝向尖端的氧气通量可以通过受阻扩散来调节。接近衬底使氧流量减小，氢放电时间延长，OCP（β→α）负移。结果是一致的混合电位由于氧还原平衡的氢化物氧化的速率。该方法是通用的，适用于其他混合电位过程中的腐蚀或催化。
This study demonstrates how the potentiometric mode of the scanning electrochemical microscope (SECM) can be used to sensitively probe and alter the mixed potential due to two independent redox processes provided that the transport of one of the species involved is controlled by diffusion. This is illustrated with the discharge of hydrogen from nanostructured Pd hydride films deposited on the SECM tip. In deareated buffered solutions the open circuit potential of the PdH in equilibrium between its β and α phases (OCP(β→α)) does not depend on the tip-substrate distance while in aerated conditions it is found to be controlled by hindered diffusion of oxygen. Chronopotentiometric and amperometric measurements at several tip-substrate distances reveal how the flux of oxygen toward the Pd hydride film determines its potential. Linear sweep voltammetry shows that the polarization resistance increases when the tip approaches an inert substrate. The SECM methodology also demonstrates how dissolved oxygen affects the rate of hydrogen extraction from the Pd lattice. Over a wide potential window, the highly reactive nanostructure promotes the reduction of oxygen which rapidly discharges hydrogen from the PdH. The flux of oxygen toward the tip can be adjusted via hindered diffusion. Approaching the substrate decreases the flux of oxygen, lengthens the hydrogen discharge, and shifts OCP(β→α) negatively. The results are consistent with a mixed potential due to the rate of oxygen reduction balancing that of the hydride oxidation. The methodology is generic and applicable to other mixed potential processes in corrosion or catalysis.