Investigation of the Proton Transport in Nafion® Membranes as a Function of Direction, Temperature and Relative Humidity

The conductivity of Nation, especially as a function of water content, represents an important parameter for its applications as membrane in electrochemical devices. All Nation types (105, 112, 115 and 117) exhibit a favourite swelling direction, most probably the strain direction. For this direction Nation 115 and 117 exhibit an increment up to 30 % higher than the other planar dimension. Conductance (ohm(-1)) data obtained by impedance measurements along the three dimensions of the Nation membranes do not show any remarkable anisotropy. Along all the directions, an activation energy of about 130 meV for the proton transport is found for all types of Nation, after swelling. In the longitudinal geometry, the activation energy of the conductance has been investigated in the temperature range 300-350 K as a function of relative humidity of the environment, which affects the membrane water content. The conductance and its activation energy has been found increasing by decreasing water content. This effect is, however, more pronounced for Nation 117 than for Nation 105.