Positron annihilation study of ion-exchanged forms of Nafione membrane

Positron annihilation lifetime and oxygen permeability in ion-exchanged forms (H+-, Na+-, K+-, Cu2+-, Ni2+-, and Fe3+ forms) of Nation membranes for polymer electrolyte fuel cells (PEFC's) have been investigated as a function of temperature. Exchange of H+ with Cu2+, Ni2+, or Fe3+ in Nafion decreases both the o-Ps lifetime and its intensity, being interpreted as the result of inhibition and quenching of Ps. For the H+, Na+, and K+-forms good correlations were observed between the logarithm of the O-2 permeability and o-Ps lifetime (free volume size) at different temperatures indicating the important role played by the free volume in O-2 permeation. Considerable downward deviation of the correlations for the Na+- and K+-forms from the litform revealed the importance of polymer stiffening in O-2 permeation. (C) 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim