“…The contaminant may either exist in the membrane before use or enter into the membrane with the fuel due to the corrosion of piping or stack materials. In their series of studies, Okada and coworkers [28][29][30][31][32][33][34][35] found that for a Nafion R membrane, the attraction of some impurity ions is larger than that of the H þ cation, and the sequence is Fe 3þ >Ca 2þ >Ni 2þ >Cu 2þ >Na þ , which implies that an ion of higher valence has a greater attraction to the membrane. Since the conductivity of the membrane is linearly proportional to the number of H þ ions in the membrane, the conductivity of the membrane decreases as the number of impurity ions increases.…”