Hierarchical hollow silica shells for scalable and passive superinsulation

Porous silica materials are highly valued for their thermal management potential, with their high porosity and large surface area making them ideal for insulation. However, challenges persist in their practical manufacturing and in establishing clear relationships between their structure and insulation performance. Here, we report a rapid 10-minute gelation process under ambient temperature and pressure conditions to enable scalable manufacturing of tunable SiO₂ hollow spheres. By systematically investigating the effects of synthetic conditions, the resulting SiO₂ hollow spheres demonstrate a thermal conductivity as low as 15 mW m⁻¹ K⁻¹ and porosity exceeding 98 %. We found through simulations that a higher contact area between hollow silica particles leads to increased thermal conductivity. Additionally, we incorporated hollow silica into ceramic fibers, which presents additional advantages for thermal protection against transient high-temperature loads by effectively delaying heat propagation through heat absorption and self-extinguishing behavior in the presence of fire. Notably, the production process features a carbon footprint of 17.07 kg CO₂/kg and a production yield of up to 40 %, striking a balance between performance and sustainability. This study marks a key step in advancing SiO₂ hollow spheres as effective thermal management materials.