Impedance models were developed to account for reaction mechanisms that may be responsible for the inductive impedance response often seen at low frequencies in proton exchange membrane (PEM) fuel cells. Models that incorporate reactions without surface intermediates cannot account for these inductive features. Inductive loops can be predicted by models that account for formation of hydrogen peroxide as an intermediate in a two-step oxygen reduction reaction. Hydrogen peroxide is considered to be a degrading agent for materials used in the fuel cell components (membrane, electrodes), and its formation under the fuel cell operating conditions is reported in the literature. Inductive loops can also be predicted by models that account for Pt dissolution and associated deactivation of catalytic activity. These interpretations are supported by experimental evidence reported in the literature. Interpretation of impedance spectra in terms of side reactions may prove useful for predicting the lifetime of fuel cell performance.