EXPERIMENTAL-DETERMINATION OF THE TRANSPORT NUMBER OF WATER IN NAFION-117 MEMBRANE

The transport number of water in Nafion (R) 117 membrane over a wide range of water contents is determined experimentally using a concentration cell. The transport number of water, the ratio t(o)m/z(o), is about 1.4 for a membrane equilibrated with saturated water vapor at 25-degrees-C, decreases slowly as the membrane is dehydrated, and falls sharply toward zero as the concentration of water approaches zero. The relationship between the transference number, the transport number, and the electro-osmotic drag coefficient is presented, and their relevance to water management in solid-polymer-electrolyte fuel cells is discussed. Results are compared with other data available in the literature and with the theoretical maximum.