Electrochemical Impedance Spectroscopy of (Photo)electrochemical Systems: A Practical Guide

Electrochemical impedance spectroscopy (EIS) is a powerful technique for investigating (photo)-electrochemical systems. Although several comprehensive introductions to EIS are available, the selection of experimental parameters and the subsequent data processing, fitting, and interpretation remain challenging, particularly for newcomers. Here, we address these challenges by providing a practical, beginner-oriented introduction to EIS that emphasizes both conceptual understanding and in-depth analysis. We discuss measurements under direct current and alternating current conditions, the use of equivalent circuits (ECs), and best practices for acquiring reliable and physically meaningful EIS data. To develop understanding in a modular and systematic way, we start from two well-defined benchmark systemsa metal-electrolyte interface and a silicon p-n junction diodeand then extend the analysis to a buried-junction photoelectrochemical device. This stepwise approach enables the construction and justification of a realistic EC model for the complete photoelectrochemical system and demonstrates how robust parameters can be extracted from EIS measurements.