The performance degradation and recovery of a polymer electrolyte fuel cell exposed to ammonia is described. The effect of ammonia contamination on each component of the MEA was studied using Neutron Imaging, lifetime tests, cell polarization measurements, potentiostatic measurements, and AC impedance spectroscopy. It is found that among the detrimental effects of the contaminant, mass transport and ORR kinectic are mostly affected. Reductions in electrolyte conductivity are not playing a major role in cell performance losses for the low levels of contamination studied here. Shifts in electrolyte proton activity reduce oxygen reduction reaction mixed equilibrium potential and so cell potential. In addition, cell potential might also be affected by overpotentials on the oxygen reduction reaction caused by oxidation of ammonia at cell potential above 0.7 V. It is demonstrated that cell initial performance can be recovered after contamination and ammonia-contaminated PEFC recovering mechanisms are discussed. (C) 2014 The Electrochemical Society. All rights reserved.