A Variable Resistance EIS-based (VRE) model for mass transfer kinetic simulation of capacitive deionization

Abstract

Capacitive deionization (CDI) holds strong potential for water reuse and low-energy desalination due to its environmental and operational advantages. Accurate modeling of CDI systems requires integration of experimental data that reflect real electrochemical behavior. However, existing models often neglect key electrode and interfacial parameters, limiting their ability to capture dynamic coupling among electric fields, ion transport, and charge storage. To address this, this study proposed a Variable Resistance EIS-based (VRE) model for mass transfer kinetic modeling, which is developed based on parameters fitted from electrochemical impedance spectroscopy (EIS). Key equivalent circuit elements such as series resistance, charge transfer resistance, and double-layer capacitance are extracted from EIS measurements to construct a physically constrained dynamic equivalent circuit model. This model is embedded within a multiphysics framework to resolve electric field distribution, ion migration, and fluid transport in a coupled manner. A concentration-dependent correction for electrolyte conductivity is further introduced to reflect the evolving electrode behavior during CDI operation, enhancing the model physical reliability and predictive accuracy. Validation under various operating conditions and CDI modes confirms that the model accurately captures the effects of influent concentration, electrode size, and flow rate, and reproduces system responses under constant current charging and recirculating flow. This method outperforms conventional empirical models in both theoretical rigor and engineering applicability, offering a robust tool for CDI system design and optimization.