Salty Silicon Synthesis: Utilization of NaCl -KCl Salt Mixtures to Assist in the Aluminothermic Reduction of Fumed SiO2

Porous silicon (p-Si) is a promising material for diverse green energy applications, including use as a negative electrode in lithium-ion batteries, solar-driven fuel production, and on-demand hydrogen generation. Conventional production methods involve the use of hydrofluoric acid etching of bulk Si or magnesiothermic reduction of silica which are limited by hazards, wastefulness, or risk of thermal runaway. Aluminum metal offers a safer, more sustainable alternative to magnesium, as it is abundant from scrap sources and easily recycled. However, existing aluminothermic reduction methods typically require AlCl3 salt, which is volatile, difficult to recycle, and demands long reaction times. This study explores a salt-mediated approach using a 1:1 wt mixture of NaCl and KCl to facilitate the reduction of fumed silica with aluminum metal. This process yields p-Si at ~83% in just one hour at 850 °C. The resulting material exhibits high reactivity, producing up to 1476 ± 51 mL of hydrogen per gram of Si within ~5 minutes, using various water sources including seawater. These findings demonstrate a safer, faster, and more scalable route to functional porous silicon for on-demand hydrogen generation and other sustainable energy applications.