原位 AFM-SECM 测量的数值校正,Analytical Chemistry

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原位 AFM-SECM 测量的数值校正
Analytical Chemistry ( IF 6.7 ) Pub Date : 2021-09-03 , DOI: 10.1021/acs.analchem.1c00770
Alex Mirabal ₁ , Scott Calabrese Barton ₁

Affiliation

传质受限催化和膜运输可以通过活性表面周围的浓度分布来表征。扫描电化学显微镜 (SECM) 是一种用于测量浓度分布的工具；然而，由于扩散受阻，尖端的存在和几何形状会扭曲这些轮廓，这反过来又会改变催化表面的化学行为。为了充分表征表面特征（如催化位点）的行为，必须考虑并分析消除尖端存在的影响。在这项工作中，基于原子力显微镜的 SECM (AFM-SECM) 对聚四氟乙烯 (PTFE) 和金电极表面的测量分别用于测量负反馈和正反馈接近曲线。通过用有限元方法 (FEM) 模型对这些接近曲线进行逆拟合，我们推导出表征尖端存在影响的动力学和几何尖端参数。可以在模型中去除尖端效应以估计不存在尖端的情况下的浓度分布和反应特性。由于尖端的存在，观察到表面上方一个尖端半径处的浓度最大增加 120%，其中浓度场垂直压缩，与表面特征尺寸和尖端分离成比例。锥形 AFM-SECM 尖端具有更高的尖端高度与底座尺寸之比，与圆盘形 AFM-SECM 尖端相比，引入的浓度失真更小。可以在模型中去除尖端效应以估计不存在尖端的情况下的浓度分布和反应特性。由于尖端的存在，观察到表面上方一个尖端半径处的浓度最大增加 120%，其中浓度场垂直压缩，与表面特征尺寸和尖端分离成比例。锥形 AFM-SECM 尖端具有更高的尖端高度与底座尺寸之比，与圆盘形 AFM-SECM 尖端相比，引入的浓度失真更小。可以在模型中去除尖端效应以估计不存在尖端的情况下的浓度分布和反应特性。由于尖端的存在，观察到表面上方一个尖端半径处的浓度最大增加 120%，其中浓度场垂直压缩，与表面特征尺寸和尖端分离成比例。锥形 AFM-SECM 尖端具有更高的尖端高度与底座尺寸之比，与圆盘形 AFM-SECM 尖端相比，引入的浓度失真更小。

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Numerical Correction of In Situ AFM-SECM Measurements

Mass-transport-limited catalysis and membrane transport can be characterized by concentration profiles surrounding active surfaces. Scanning electrochemical microscopy (SECM) is a tool that has been used to measure concentration profiles; however, the presence and geometry of the tip can distort these profiles due to hindered diffusion, which in turn alters chemical behavior at the catalytic surface. To fully characterize the behavior of surface features such as catalytic sites, it is essential to account for and analytically remove the effect of tip presence. In this work, atomic force microscopy-based SECM (AFM-SECM) measurements over poly(tetrafluoroethylene) (PTFE) and gold electrode surfaces are used to measure negative and positive-feedback approach curves, respectively. By inversely fitting these approach curves with a finite element method (FEM) model, we derive kinetic and geometric tip parameters that characterize the effect of tip presence. Tip effects may be removed in the model to estimate concentration profiles and reaction properties for the case where no tip is present. A maximum 120% increase in the concentration at one tip radii above the surface is observed due to the presence of the tip, where the concentration field is compressed vertically, in proportion to surface feature size and tip separation. Conical AFM-SECM tips, with a higher ratio of tip height to the base size, introduce less concentration distortion than disk-shaped AFM-SECM tips.

更新日期：2021-09-21

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