Following the switch to dry gas after sample 59 (#2), membrane resistance rises to 1.08 mΩ and subsequently decreases upon switching back to humidified air. Similar trends are observed for anodic charge transfer resistance and cathodic double-layer capacitance, as increased water content adversely affects proton transport in the ionomer. The correlation coefficients between these parameters and water content are depicted in Fig. and F, with 0.666 and 0.655 for anodic charge transfer resistance and cathodic double-layer capacitance, respectively, when considering all samples. This robust correlation supports impedance spectroscopy-based water content estimation, signifying a nonlinear relationship between EIS measurement and overall water content.