Liu Eric Z, Popescu Sofia Rivalta, Eden Alexander, Chung Julia, Roehrich Brian, Sepunaru Lior
Department of Chemistry and Biochemistry, University of California at Santa Barbara, Santa Barbara, CA, 93106, United States.
Department of Chemical Engineering, University of California, Santa Barbara, Santa Barbara, CA, 93106, United States.
Electrochim Acta. 2023 Dec 20;472. doi: 10.1016/j.electacta.2023.143397. Epub 2023 Oct 26.
Blocking electrochemistry, a subfield of single-entity electrochemistry, enables in-situ sizing of redox-inactive particles. This method exploits the adsorptive impact of individual insulating particles on a microelectrode, which decreases the electrochemically active surface area of the electrode. Against the background of an electroactive redox reaction in solution, each individual impacting particle results in a discrete current drop, with the magnitude of the drop corresponding to the size of the blocking particle. One significant limitation of this technique is "edge effects", resulting from the inhomogeneous flux of the redox species' diffusion due to increased mass transport to the edge of the disk electrode surface. "Edge effects" cause increased errors in size detection, resulting in poor analytical precision. Here, we use computational simulations to demonstrate that inhomogeneous diffusional edge flux of quasi-reversible redox species is mitigated at lowered overpotentials. This phenomenon is further illustrated experimentally by lowering the applied potential such that the system is operating under a kinetically-controlled regime instead of a diffusion-limited regime, which mitigates edge effects and increases particle sizing precision significantly. In addition, we found this method to be generalizable, as the precision enhancement is not limited to geometrically spherical particles but also occurs for cubic particles. This work presents a simple, novel methodology for edge effect mitigation with general applicability across different particle types.
阻断电化学作为单实体电化学的一个子领域，能够对氧化还原惰性颗粒进行原位尺寸测定。该方法利用单个绝缘颗粒对微电极的吸附作用，这会减小电极的电化学活性表面积。在溶液中电活性氧化还原反应的背景下，每个撞击颗粒都会导致离散的电流下降，下降的幅度与阻断颗粒的大小相对应。该技术的一个重大局限是“边缘效应”，这是由于氧化还原物质扩散通量不均匀导致向圆盘电极表面边缘的传质增加所致。“边缘效应”会导致尺寸检测误差增大，从而导致分析精度较差。在此，我们通过计算模拟证明，在较低的过电位下，准可逆氧化还原物质的不均匀扩散边缘通量会得到缓解。通过降低施加电位，使系统在动力学控制 regime 而非扩散限制 regime 下运行，进一步通过实验说明了这一现象，这减轻了边缘效应并显著提高了颗粒尺寸测定精度。此外，我们发现该方法具有通用性，因为精度提高不仅限于几何球形颗粒，对于立方颗粒也会出现。这项工作提出了一种简单、新颖的减轻边缘效应的方法，对不同类型颗粒具有普遍适用性。
