Several different start-up and shutdown processes of a fuel cell were investigated in this paper by measuring cathode, anode and membrane potentials respectively versus reference hydrogen electrode (RHE). The membrane potential was measured by using thin copper wire sandwiched between two membranes. During the formation of hydrogen/air boundary at the anode caused by unprotected start-up and shutdown, the in-plane potential difference between membrane inlet and outlet was measured to be as high as 0.8V, and the interfacial potential difference between cathode and membrane outlet increased to about 1.6V, which in turn would cause carbon corrosion. Appropriate start-up and shutdown processes were suggested to avoid the formation of hydrogen/air boundary. (C) 2008 Elsevier B.V. All rights reserved.