Deconvolution and Estimation of Water Diffusion in Sulfonated Polyethersulfone Membranes Using Diffusion-Weighted Inversion Recovery.
An NMR method was applied for the deconvolution of specific water in sulfonated polyether sulfone membranes, where sulfonated polyethersulfone is a proton-conducting polymer in polymer electrolyte membrane fuel cells. The distribution of (1)H longitudinal relaxation times obtained by the inverse Laplace method was utilized to estimate the volume fraction of proton species as a function of relative humidity (RH). The relaxation time distribution clearly revealed two distinguished peaks on the order of 10(-3) and 10(-2) s, which corresponded to water in the larger and smaller channels for proton transports, respectively. We applied a pulse sequence to understand the water species by diffusion-weighted inversion recovery, which led to individual self-diffusion coefficients for deconvoluted water by using the longitudinal relaxation time. At 30% RH, the diffusion coefficient of water in small-sized channels is greater than that in large-sized channels. On the other hand, the diffusion coefficients of protons with smaller and larger water channels are almost the same at 50, 70, and 90% RH.
Takahiro
T
Ohkubo
‡FC-Cubic, National Institute of Advanced Industrial Science and Technology (AIST), 2-41-6 Aomi, Koto-ku, Tokyo 135-0064, Japan.
Akihiro
A
Ohira
Yasuhiko
Y
Iwadate
Laplace transform; NMR; proton exchange membrane fuel cells; proton transports; water channel