This study shows the effect of phosphotungstic acid (PWA) blended into a sulfonated poly(ether ether ketone) (SPEEK) and poly(ethylene glycol) (PEG) crosslinked membrane on the membrane's electrochemical and mechanical properties. The PWA weight percentage was varied from 0 to 50%. All of the membranes were equilibrated with water at room temperature (27 °C) and elevated temperature (60 °C), and their properties were investigated. A scanning electron microscope with energy dispersive X‐ray was used to ascertain the tungsten concentration remaining in the membrane after water treatment. A systematic decrease in tungsten concentration was seen with the increase in the initial PWA percentage. The membrane blended with 10% PWA showed the best properties, having the highest conductivity (0.11 S cm−1), mechanical strength, and chemical stability. Membranes with 10% PWA and without PWA were studied in a H2/O2 fuel cell. The membrane blended with 10% PWA gave 33% more power density than the membrane without PWA. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46667.