Abstract: In an embodiment, the present disclosure pertains to a metal oxide-coated nanofiber yarn. In some embodiments, the metal oxide-coated nanofiber yarn includes a plurality of twisted carbon nanofibers. In some embodiments, each twisted carbon nanofiber includes a porous hollow fiber. In some embodiments, each twisted carbon nanofiber includes metal oxide nanoparticles coated on a surface thereof. In some embodiments, an outer surface of each twisted carbon nanofiber, an inner surface of each twisted carbon nanofiber, and holes or channels of a main fiber skeleton of the plurality of twisted carbon nanofibers with the possibility of transferring a metal ion are covered by the metal oxide nanoparticles. In a further embodiment, the present disclosure pertains to methods of making the metal oxide-coated nanofiber yarn. In an additional embodiment, the present disclosure pertains to a structural supercapacitor utilizing the metal oxide-coated nanofiber yarn.