The dynamics of the STR PEM fuel cell are much simpler to analyze than experiments performed with a typical fuel cell test station. The STR PEM fuel cell is one-dimensional, so the current, voltage and membrane resistance are all spatially uniform. The water content only varies transverse to the membrane. All the system variables may be directly related to the anode and cathode effluent compositions. No spatial integration of the current density, or membrane water content is necessary.