Constructing facile proton-conduction pathway within sulfonated poly(ether ether ketone) membrane by incorporating poly(phosphonic acid)/silica nanotubes

• Poly(phosphonic acid)/silica nanotubes with diverse aspect ratios were prepared.
• The nanotubes were incorporated into SPEEK to prepare composite membrane.
• Effect of aspect ratios of the nanotubes on proton conductivity was studied.
• The composite membranes showed enhanced proton conductivity and stability.

The objective of this study is to exploit the one-dimension structure and good proton conduction of phosphorylated silica nanotubes for high proton conductivity of proton exchange membrane (PEM). Three types of poly(vinylphosphonic acid-co-divinylbenzene)/silica nanotubes with different aspect ratios are synthesized and incorporated into the sulfonated poly(ether ether ketone) (SPEEK) matrix to prepare composite membranes. The poly(vinylphosphonic acid) segments in the nanotubes could construct facile proton-conduction pathway along this one-dimensional nanostructure. The nanotubes with high aspect ratio exhibit more pronounced effect in elevating the proton conductivity of membranes, revealing the importance of continuity of conduction pathway on proton transport. The membrane incorporated with the nanotubes of the largest aspect ratio of 45.9 exhibits the highest proton conductivity of 0.1032 S cm−1 at 30 °C, 100% RH, which was 84% higher than that of SPEEK control membrane. Moreover, the nanotubes can reduce the methanol permeability, and improve mechanical stability of the membranes.