NMR and X-ray diffraction study of the phases of zirconium phosphate incorporated in a composite membrane Nafion®-ZrP

Abstract

Zirconium Phosphate (ZrP) inside a composite membrane Nafion-ZrP was studied by combining wide angle X-ray diffraction (XRD) and high-resolution solid-state 31P Nuclear Magnetic Resonance (NMR) under magic angle spinning conditions (MAS). We have, at first, investigated the physical features of ZrP powders that were prepared ex situ under different conditions leading to either amorphous or crystalline α-ZrP. ZrP incorporated into Nafion® membranes (in situ ZrP) was then studied. Informations obtained from X-ray and NMR data clearly show that the in situ ZrP is not in a purely crystalline phase. The presence of broad peaks in the X-ray spectra proves that the compound inside the membrane is semi-crystalline. This result is confirmed by MAS 31P NMR since the NMR spectra of in situ ZrP and ex situ semi-crystalline ZrP powder are alike. Moreover, the NMR analyses demonstrate that the phosphate groups can be found in three different connectivities with phosphorous atoms surrounded by either 2, 3 or 4 OZr bonds., with predominantly 3 OZr bonds being favored.