This study quantitatively describes the carbonate- and bicarbonate-forming reaction mechanisms in an operating alkaline exchange membrane fuel cell that occur as a result of carbon dioxide in the cathode gas stream. A transient, spatially-averaged theoretical model was created for this study and validated to experimental data from the literature. Results present the prediction of the membrane's ionic conductivity as a function of operating conditions and membrane properties. The self-purging phenomenon was observed and studied, as well as the emission of carbon dioxide from the membrane during operation. Following the conductivity study, suggestions can be made for optimal operating conditions and membrane properties to improve fuel cell performance in the presence of carbon dioxide. (C) 2017 The Electrochemical Society. All rights reserved.