The dynamics of the stirred tank reactor polymer electrolyte membrane (STR-PEM)fuel cell arise from the balance between water production and water removal within the cell. This results in STR-PEM fuel cell steady-state multiplicity, remarkably analogous to that of an autocatalytic exothermic STR. Model flooding effects in the cathodeside catalyst/gas diffusion layer by accounting for relevant mass-transport processes is presented. We use the resulting STR-PEM fuel cell model as a building block to construct approximations of more conventional integral (plug flow) type fuel-cell reactors. This approach bypasses more complicated, distributed gas diffusion layer models. Connecting several STR-PEM fuel cells in series, the effects of four operating parameters (temperature, external load resistance, inlet hydrogen and inlet oxygen flow rates) on the current evolution in each tank can be monitored and rationalized. (c) 2006 American Institute of Chemical Engineers AIChE J, 52: 3902-3910, 2006.