Surface attachment of protonated polyimidazolium monolayer on titanate nanotubes as a novel proton conductor

A novel proton conductor has been designed by the surface immobilization of protonated polyimidazolium monolayer on titanate nanotubes (TiNTs) through a polymer brush strategy. 2,2′-Azobis(2-methylpropionitrile) (AIBN)-type initiators are first attached to TiNTs followed by a free radical polymerization of protonated 1-vinylimidazole (VyImBF₄) on the surface. The chemical structure of the resulting poly(VyImBF₄)-modified TiNTs is verified by Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). TGA curve indicates their good thermal stability. The maximum proton conductivity achieves 6.74 × 10⁻⁴ S cm⁻¹ at 200 °C under dry condition and 3.60 × 10⁻² S cm⁻¹ at 120 °C under 100% humidity, respectively, when the polymerization is carried out under a polymerization time of 3 h and an immobilized initiator concentration of approximately 42.4 mmol L⁻¹. The proposed preparation of poly(VyImBF₄)-modified TiNTs would give a new idea for the design of other ion conductors.