Polymer electrolyte membrane (PEM) degradation in electrolysis mode is simulated through a Fenton model that includes all major involved electrochemical reactions. Supportive experimental investigations on the effect of hydrogen peroxide and iron impurities are carried out in an ex-situ set-up, where the results are utilized to fit model parameters. The experiments reveal a high dependence of fluoride emission on iron concentration, which catalyzes the reaction, and identifies hydrogen peroxide as a necessary precursor for destructive hydroxyl radical formation. Simulations of in-situ operation reveal that elevated current is favorable in terms of lower fluoride emission, as the radicals are depleted by side reactions. Temperatures above 80T significantly accelerate membrane thinning, where the step from 80 degrees C to 90 degrees C more than doubles thinning after 500 h.