A transient, isothermal, two-dimensional model coupling cell performance and chemical membrane degradation in a polymer electrolyte membrane fuel cell (PEMFC) is developed. The model is based on the conservation of and thermodynamic equilibrium between charged and neutral species, including radicals. The model is validated against experimental polarization behavior and chemical degradation under an open circuit voltage (OCV) hold test at 368.15 K. The four-step chemical degradation of a PFSA-based membrane is assumed to start by an attack by hydroxyl radical at the terminal ether bond in the side chain. The source of the attacking hydroxyl radical is an indirect hydrogen peroxide formation and the subsequent decomposition at Fenton's reagent in the membrane. Simulation of degradation rate (defined as the loss of cell voltage with time at a fixed cell operating condition and at a point of time with a known degradation history) under an OCV-hold test agree qualitatively with the degradation rates reported in the literature. (C) The Author(s) 2018. Published by ECS.