Porous multi-metal oxide nanotubes and methods of making the same are disclosed. In one aspect, there is provided a method of making porous multi-metal oxide nanotubes comprising: (a) preparing a mixture comprising a metal-acetylacetonate precursor, polyacrylonitrile (PAN), and a solvent component; and (b) preparing the nanocomposite from the mixture, wherein the metal of the metal-acetylacetonate precursor includes a non-radioactive alkali metal stable isotope and a non-radioactive alkaline earth metal stable isotope. Accordingly, a porous multi-metal oxide nanotube having a single-phase multivalence can be obtained in a high yield without using harmful chemicals. In addition, the polymer electrolyte membrane including the porous multi-metal oxide nanotubes may maintain and improve mechanical strength and thus may maintain durability even during battery operation, and may have improved proton conductivity even at low humidity. Fuel cells including the polymer electrolyte membranes may have improved performance.
