EIS stands out as an established tool, perhaps the most widely used characterisation method in many electrochemical devices, for investigating the various processes occurring inside fuel cells in a non-destructive way through current or voltage perturbation, which is intensively applied for characterisation, control and diagnosis of water management failures . The total cell resistance is divided into three parts with different time constants in the frequency domain: Ohmic resistance, charge transfer resistance, and mass transport resistance . Protons can be transported more easily through water-filled clusters or ionic channels after the membrane has absorbed more water, resulting in reduced Ohmic resistance, where membrane resistance is the main contributor. Similarly, the charge transfer resistance decreases with increasing relative humidity (RH), given the crucial role of water content in facilitating proton conduction at the triple-phase boundary in the catalyst layer . The mass transport resistance is also strongly correlated to water inside the cell, as flooding in the gas diffusion layer (GDL) will hinder the transport of reactants through the porous structure and catalyst sites . Toyota has successfully validated and implemented a water content control system based on AC impedance measurement , making a -30℃ cold start possible. A high resistance corresponds to reduced water content, leading to a decline in average voltage; when the membrane is humidified to saturation, the voltage becomes unstable. Keeping the resistance within a certain range helps the fuel cell system operate efficiently and stably. It is still possible to increase the accuracy of the water content control, because only Ohmic resistance is used in this study ,