Embodiments of a safe, low-temperature reaction system and method for preparing porous silicon are disclosed. The porous silicon is prepared from porous silica, a low-melting metal halide, and a metal comprising aluminum, magnesium, or a combination thereof. Advantageously, embodiments of the disclosed methods can be performed at temperatures ≤400° C. Silicon produced by the disclosed methods has a porosity that is equal to or greater than the porous silica precursor. The porous silicon is suitable for use in electrodes.