Application of HTO as radioactive tracer to investigate water transport properties of fluoropolymer-based fuel-cell electrolyte membranes

Sekine, Toshihiko; Sawada, Shinichi; Yamaki, Tetsuya; Asano, Masaharu; Suzuki, Akihiro*; Terai, Takayuki*; Maekawa, Yasunari

A tracer permeation technique was applied as the only way to detect water transport in polymer electrolyte membranes (PEMs) immersed in a water/methanol mixture. As a first step, we investigated the applicability of a tritiated water (HTO) tracer method comparing with the results from a heavy oxygen water (HO) tracer. According to a simple isotopic-exchange theory, the measured HTO permeation coefficient, P(HTO), is assumed to depend on the abundance ratio between HO and CHOH in the solution used for the permeation experiments. This assumption enabled us to estimate the effective permeability of HTO, P(HTO). Importantly, we noticed a rather small difference between the P(HTO) and P(HO) values, which probably indicates that HTO mobility was affected by the different T/H substitution rates due to hydrogen-bonding interaction with polar sulfonic acid groups in PEMs.