Ohmic Drop Compensation in Electrochemical Measurement
- 2021年第27卷 
对工作电极与参比电极之间的溶液电阻(Ru)进行准确的欧姆电压降补偿是获取可靠的电化学实验结果的前提,但测量中该如何进行补偿尚未建立规范的操作流程。本文首先探究了工作电极与Luggin毛细管末端距离对Ru的影响。随后对比了Autolab PGSTAT 302N、CHI系列恒电位仪的交流阻抗法与CHI系列恒电位仪所测得Ru的差别。并且以铂电极上的氢析出反应为例,探究了灵敏度、补偿百分比以及仪器等因素对补偿后HER极化曲线带来的影响。深入讨论了产生这些偏差的原因,最后给出了规避和减轻此类问题以实现准确有效的欧姆电压降补偿的建议。The solution resistance (Ru) between the working electrode (WE) and the reference electrode (RE) may lead to significant Ohmic drop (iRu) and deviation of actually applied potential at the WE to the desired ones in electrochemical measurement. In the case of high current or large Ru, iRu compensation is imperative. Errors associated with insufficient compensation of theiRu drop may significantly affect the accuracy of data measured by conventional electrochemical methods, which may consequently result in wrong judgment and conclusions. In this article, we discuss important factors which may affect the accuracy of iRu compensation as well as ways how to eliminate such errors through examples. Since Ru will be changed sensitively with the distance between the tip of the Luggin capillary of the RE and the WE, it should always be kept at a fixed distance (usually as close to the surface of the WE as possible but without affecting the behavior of electrode processes) during a set of measurements. In addition to the structure of the cell (relative positions of WE and RE), the methods of measuring Ru, current sensitivity for recording data, percentage of Ru compensation, and instruments could cause the result to be deviated from the actual value, which are demonstrated by taken hydrogen evolution reaction on Pt electrode as model reactions measured using both CHI and Autolab PGSTAT 302N potentiostats. Comparing the AC impedance method with the potential step method in the automatic compensation function of CHI potentiostat, theRu measured by the potential step method was smaller than the Ru measured by the AC impedance method and the actual value. It is suggested to use the AC impedance method to measure Ru, input the resistance value manually and complete the compensation by the instrument. Current sensitivity may limit the maximum Ru to be compensated, hence, one should select the right current sensitivity before recording data. In particular, when compensating by manual input using some types of potentiostat, one should be aware that the software may show the completely compensated resistance, in reality, however, the part of the resistance that exceeded the upper limit will not be compensated successfully. Furthermore, the percentage ofRu compensation should be carefully optimized before carrying out the actual measurements, through comparing curves recorded with different percentages of compensation. Moreover, the same compensation level but conducted with different instruments may lead to significantly different results, using the same instrument in a series study is recommended to mitigate related errors. A set of strict compensation standards applied to all instruments and electrochemical systems is difficult to be established. Hence, we suggest carrying out some control experiments to optimize the iRu compensation before the actual measurements, and write in detail their compensation methods and parameters in the published results, especially the factors mentioned in this paper.