Measuring the water content of polymer electrolyte membranes using double points of proton magic angle spinning nuclear magnetic resonance data

Although the water content in polymer electrolyte membranes (PEMs) is a very important parameter for controlling their performance, measuring it is difficult because strong acidic groups such as sulfonic acid in PEMs make them very hygroscopic. In this study, we demonstrate that the proton magic-angle-spinning nuclear magnetic resonance spectroscopic data of a Nafion PEM accompanied by weight data measured for two different water contents can be used to determine the water content of dry as well as swollen PEM. The advantages of this method are that completely dry-PEM weight can be obtained without perfectly removing water from the PEM and no specific drying condition is required. Further, the advantages and disadvantages of the proposed method and calibration curve methods are discussed. The proposed method can be applied to various PEMs provided accurate equivalent-weight values for the PEMs are available. [Display omitted] •Completely dry-PEM weight is obtained without completely removing water.•No specific drying condition is required for this water content measurement method.•Remaining and free-channel water contents of the PEM are separately measured.•This analysis method can be applied to other PEMs.•MAS technique enhances the S/N of water signals by narrowing the line widths.