A one-dimensional, dynamic, two-phase, isothermal model of proton exchange membrane fuel cell systems using a finite-difference approach has been developed. This model balances the simplicity of lumped-parameter models with the detailed accuracy of computational fluid dynamics models, offering precise internal state descriptions with low computational demand. The model’s static behavior is validated experimentally using polarization curves. In addition, a novel physical parameter, the limit liquid water saturation coefficient (s_lim), is introduced in the overvoltage calculation, replacing the traditional limit current density coefficient (i_lim). This new parameter links the voltage drop at high current densities to the amount of liquid water present in the catalyst layers and the operating conditions of the fuel cell. Additionally, it has been observed that s_lim is influenced at least by the gas pressure applied by the operator. This newly established link is promising for optimizing the control and thereby improving the performance of fuel cells.