A steady-state, two-dimensional model is presented and discussed that descr
ibes the water transport in a proton exchange membrane fuel cell. Concentra
ted solution theory is used to describe the transport of water in the membr
ane, and of water vapor and liquid water in the electrodes. The inclusion o
f the liquid water transport into the model turned out to be essential for
explaining recent experimental results on the effective drag coefficient an
d its dependence on operating conditions as well as on variations of the co
mponents that constitute the membrane electrode assembly. (C) 2001 The Elec
trochemical Society.