To obtain a porous Si film, the co-deposited films were annealed on a hotplate under Ar for 3 hours at 200-300 °C: For films with ≤ 60 at% Si, 200 °C was enough to induce crystallization of the Si and phase separation between the Si and Al as determined by XRD, Figure . For higher Si content, 300 °C was used. To dissolve the Al and obtain a porous Si film, the steel disks were immersed in 1 M (aq) KOH solution at room temperature for 1-2 minutes until hydrogen bubbling stopped. After dealloying, to remove residual KOH and water, the films were immersed in MilliQ water (twice) and isopropanol for 5 minutes each, dried in a vacuum oven at 60 °C for 1 hour and cooled to room temperature while under vacuum. Stainless steel substrates were chosen instead of Cu foil, because extensive delamination was observed during KOH immersion in the case of the Cu foil.