A major challenge to the application of Pt-transition metal alloys in PEMFCs is the stability of the Pt alloy. This work intends to evaluate the durability of PtCo/C cathode catalyst in a dynamic fuel cell environment with continuous water fluxing on the cathode. A potential cycling test between 0.87 and 1.2V versus RHE was applied to the system to illustrate how cobalt or platinum dissolution might affect the cell performance. The results indicate that cobalt dissolution neither detrimentally reduces the cell voltage nor dramatically affects the membrane conductance. Cell performance enhancement by PtCo/C over Pt/C catalyst has been sustained over 2400 cycles and the overall performance loss of the PtCo/C membrane electrode assemblies (MEAs) was less than that of the Pt/C MEA. Potential cycle testing has been shown to accelerate cobalt dissolution as indicated in a substantial loss of catalyst activity in the 1st 400 potential cycles. (c) 2005 Elsevier B.V. All rights reserved.