Most recently, a three-dimensional transient model, coupling the species transport, gas flow, and water transport through the membrane with electrochemical kinetics in catalyst layers, was developed by Wang and Wang [18]. The transient model considers vastly different time scales characteristic of the electrochemical double layer discharging, gas transport, and membrane hydration, respectively. In addition, numerical exploration of the transients after a step change in cell voltage or inlet humidity was carried out. However, to date no study has been carried out on the transient response of a low-humidity PEFC to step changes in current load, which is the standard operational mode of load changes in the automotive application.