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

Abstract

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. 31P 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. 1H−31P heteronuclear correlation (HetCor) NMR and 1H−31P 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. 19F NMR experiments showed that the fluorine in the −SO2F group of the Nafion-F precursor is fully replaced. 31P{19F} rotational-echo double-resonance (REDOR) experiments measured a P−F internuclear distance of ∼0.4 nm, which showed that the proazaphosphatranium is covalently attached to Nafion through a S−P bond. 13C NMR and 1H−13C HetCor spectra indicated that the proazaphosphatranium structure is maintained even after the microwave treatment at 180 °C and also showed indications of entrapped dimethylformamide solvent.