Impedance Modeling for Mixed Conductors with Simultaneous Insertion & Electrocatalytic Reactions: A Case Study of Transition-Metal Hydroxides in Aqueous Electrolyte

Electrochemical impedance spectroscopy (EIS) is commonly used to investigate the kinetics of mixed ionic–electronic conductor (MIEC) electrodes. Across various applications, MIECs exhibit ionic (e.g., insertion) and/or electronic electrocatalytic) charge transfer reactions at electrode/electrolyte interface. Bulk storage and transport carriers also couple with these interfacial reactions. Here, we build a generalized, physics-based model for an ion-blocking current collector explore how bulk resistance, chemical capacitance, DC polarization affect response. Using transition metal hydroxides as case study, provide guidance on extracting reaction or resistance from Nyquist plots in interface- bulk-controlled conditions, respectively. Generalizing our EIS analysis enables robust MIEC diverse set systems.