Electrochemical Impedance Imaging on Conductive Surface

Electrochemical impedance spectroscopy (EIS) is a powerful tool to measure and quantify the system impedance. It allows to characterize the electrocatalytic and battery reactions. However, EIS only provides an average result from the entire electrode surface. Here, we demonstrated a reflection impedance microscope (RIM) which allows us to image and quantify the localized impedance on conductive surfaces. The RIM is based on the sensitive dependence between the materials’ optical properties, such as permittivity, and their local surface charge densities. According to the Drude model, the permittivity of metal surface is a function of charge density. Therefore, the localized charge density variations introduced by the impedance measurements will lead to the optical reflectivity changes on the electrode surfaces and can be captured with a cameras. Our experiments demonstrated that the reflectivity modulations are linearly proportional to the surface charge density on the electrode and the measurements show good agreement with the simple free electron gas model. The localized impedance distribution was successfully extracted from the reflectivity measurements together with the Randles equivalent circuit model. In addition, RIM is used to quantify the impedance on different conductive surfaces, such as indium tin oxide glass slide, fluorine-doped tin oxide glass slide, and stainless steel electrodes. A PDMS patterned electrode surface was used to demonstrate the impedance imaging capability of RIM. In the end, a single cell impedance imaging was obtained by RIM.