Interdepartmental Program in Biomedical Science and Engineering, University of California at Santa Barbara.
Interdepartmental Program in Biomedical Science and Engineering, University of California at Santa Barbara; Department of Chemistry and Biochemistry, University of California at Santa Barbara.
J Vis Exp. 2023 Aug 4(198). doi: 10.3791/65116.
Nanoimpact electrochemistry enables the time-resolved in situ characterization (e.g., size, catalytic activity) of single nanomaterial units, providing a means of elucidating heterogeneities that would be masked in ensemble studies. To implement this technique with redox inactive particles, a solution-phase redox reaction is used to produce a steady-state background current on a disk ultramicroelectrode. When a particle adsorbs onto the electrode, it produces a stepwise reduction in the exposed electrode area, which produces, in turn, a stepwise decrease in the current commensurate with the size of the adsorbing species. Historically, however, nanoimpact electrochemistry has suffered from "edge effects," in which the radial diffusion layer formed at the circumference of the ultramicroelectrodes renders the step size dependent not only on the size of the particle but also on where it lands on the electrode. The introduction of electrocatalytic current generation, however, mitigates the heterogeneity caused by edge effects, thus improving the measurement precision. In this approach, termed "electrocatalytic interruption," a substrate that regenerates the redox probe at the diffusion layer is introduced. This shifts the rate-limiting step of the current generation from diffusion to the homogeneous reaction rate constant, thus reducing flux heterogeneity and increasing the precision of particle sizing by an order of magnitude. The protocol described here explains the set-up and data collection employed in nanoimpact experiments implementing this effect for improved precision in the sizing of redox in-active materials.
纳米冲击电化学能够实时原位表征（例如，尺寸、催化活性）单个纳米材料单元，提供了一种阐明在整体研究中被掩盖的异质性的方法。为了在不具有氧化还原活性的颗粒上实现该技术，使用溶液相氧化还原反应在盘状超微电极上产生稳态背景电流。当颗粒吸附到电极上时，它会导致暴露的电极面积逐步减小，这反过来又会导致电流逐步减小，与吸附物质的尺寸成正比。然而，历史上纳米冲击电化学一直受到“边缘效应”的困扰，即在超微电极的圆周上形成的径向扩散层使得阶跃大小不仅取决于颗粒的大小，还取决于它在电极上的位置。然而，引入电催化电流产生可以减轻边缘效应引起的异质性，从而提高测量精度。在这种方法中，称为“电催化中断”，在扩散层中引入了一种可以再生氧化还原探针的基底。这将电流产生的限速步骤从扩散转移到均相反应速率常数，从而减少通量异质性，并将颗粒尺寸测量的精度提高一个数量级。这里描述的方案解释了为提高氧化还原非活性材料的尺寸测量精度而在纳米冲击实验中采用的设置和数据采集。
