High temperature proton exchange membranes prepared from epoxycyclohexylethyltrimethoxysilane and amino trimethylene phosphonic acid as anhydrous proton conductors

High temperature anhydrous proton exchange membranes based on phosphonic acid were prepared from epoxycyclohexylethyltrimethoxysilane (EHTMS) and amino trimethylene phosphonic acid (ATMP) by sol–gel process. The structures and properties of membranes with different phosphonic acid content were extensively characterized by FTIR, TG-DSC and XRD. Their proton conductivity under dry condition was also investigated under different temperature. The results show that the proton conductivity of the prepared membranes strongly depends on temperature, and the proton conductivity ranges from 8.81 × 10−5 S cm−1 at 20 °C to 4.65 × 10−2 S cm−1 at 140 °C under anhydrous condition. It indicates that the increasing temperature is favorable for congregating of the grafted–PO3H2 and increasing of the proton mobility. In addition, from the results of AFM images, it was confirmed that the continuous distribution of phosphonic acid groups is favorable for the formation of the proton transport channel, which can significantly enhance the proton conductivity of the membranes.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Hybrid membranes of Epoxycyclohexylethyltrimethoxysilane and Amino trimethylene phosphonic acid. ► The proton conductivity is 4.65 × 10−2 S cm−1 at 140 °C under anhydrous condition. ► Continuous uniform distributions of phosphonic acid groups can be observed by AFM. ► There could be hydrogen bond network within high temperature membranes.