In this study we investigate the commonly observed phenomenon whereby carbon dioxide (CO2) in the cathode gas stream (e.g., air) is absorbed and released from the anion exchange membrane fuel cell (AEMFC). Often described as "self-purging" due to the emission of the CO2 gas from the AEMFC with increased current, the mechanisms of this process are still largely unknown. Herein we provide evidence that this self-purging occurs through an electrochemical mechanism, in which bicarbonate and carbonate ions directly participate in the hydrogen oxidation reaction. After determining the nature of the self-purging mechanism, we present a series of parametric studies that investigate the fundamental effects of CO2 on the AEMFC, and discuss certain operating parameters that can be manipulated to improve cell performance. (c) The Author(s) 2019. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited.