Determination of the Structure of a Novel Anion Exchange Fuel Cell Membrane by Solid-State Nuclear Magnetic Resonance Spectroscopy

A novel anion exchange fuel cell membrane was Successfully synthesized by chemically attaching proazaphosphatranium/phosphatranium cations under microwave treatment to the sulfonic groups of Nafion-F. Solid-state nuclear magnetic resonance (NMR) techniques were employed to determine the actual structure and composition of this anion exchange membrane. P-31 NMR showed two main signals with a 2:1 intensity ratio and chemical shift changes of +89 and +46 ppm, respectively, from the main peak of phosphatranium chloride. H-1-P-31 heteronuclear correlation (HetCor) NMR and H-1-P-31 recoupling experiments indicated that the proton originally bonded to phosphorus in phosphatranium chloride is replaced in the major component of the Nafion-proazaphosphatranium/phosphatranium composite. F-19 NMR experiments showed that the fluorine in the -SO2F group of the Nafion-F precursor is fully replaced. P-31{F-19} rotational-echo double-resonance (REDOR) experiments measured a P-F internuclear distance of similar to 0.4 nm, which showed that the proazaphosphatranium is covalently attached to Nafion through a S-P bond. C-13 NMR and H-1-C-13 HetCor spectra indicated that the proazaphosphatranium structure is maintained even after the microwave treatment at 180 degrees C and also showed indications of entrapped dimethylformamide solvent.