Sulfonated poly(ether ether ketone) composite membranes based on amino‐modified halloysite nanotubes that effectively immobilize phosphotungstic acid

Abstract In this work, we prepared amino‐modified halloysite nanotubes (PEI‐DHNTs) via the co‐deposition of self‐polymerized dopamine and polyethylenimine (PEI) on the surface of nanotubes, which was confirmed by X‐ray photoelectron spectroscopy (XPS) and Thermogravimetric analysis (TGA). A series of composite proton exchange membranes (PEMs) were prepared by incorporating PEI‐DHNTs and phosphotungstic acid (HPW) into sulfonated poly(ether ether ketone) (SPEEK). It was found that both PEI‐DHNTs and HPW were well dispersed in the polymer matrix, exhibiting excellent filler‐matrix compatibility. The composite membranes demonstrated enhanced proton conductivity, reaching as high as 0.078 S cm −1 with 33.3 wt.% HPW loading, which was ~90% higher than that of SPEEK control membrane. Such improvement was mainly attributed to the strong acid–base pairs formed by PEI‐DHNT with both SPEEK and HPW, which shortened proton hopping distance and created more continuous proton conduction pathways. Furthermore, the membrane conductivity remained almost constant after 1 year's immersion in liquid water, indicating the successful immobilization of HPW in the composite membranes.