In an example of the method disclosed herein, a precipitate is formed in an aqueous mixture by mixing an SiOx precursor and an acid. The precipitate and a carbon material are added to a base, and the precipitate dissolves to form a solution having the carbon material therein. Hydrothermal synthesis is performed using the solution, and precursor nanostructures are grown on the carbon material. The precursor nanostructures on the carbon material are annealed so that the carbon material is removed and porous, one-dimensional SiOx (0