Nanomodified p- and n-type porous ultra-lightweight cementitious foams for thermal energy harvesting in precast panels

This study explores the nanomodification of cementitious foams and their assembly into a thermoelectric generator (TEG) panel. Ultra-lightweight cementitious foam with a density of 257 kg/m³ was prepared via a facile mixing composition, casting and drying method, employed to incorporate single walled carbon nanotube (SWCNT) networks via simple vacuum impregnation process of a water-based dispersion and subsequent oven drying. This straightforward process yielded p-type cementitious foams with a Seebeck coefficient of + 21.8 μV/K. Similarly, a straightforward post-treatment process was implemented for the n-type cementitious blocks via immersing the p-type foams in a concentrated Polyethyleneimine (PEI) water-based solution for 24 h followed by oven drying with a resulting, stable Seebeck coefficient of −16.9 μV/K. Crucially, although the SWCNT modification resulted in a pronounced reduction in thermal conductivity relative to the pristine foam, the modified cementitious foams maintained low effective thermal conductivity, confirming the preservation of their thermal insulating character. Additionally, both p- and n-type cementitious foams were thoroughly examined regarding their physicochemical, electronic and mechanical properties. Indicatively, the fabricated TEG-enabled building envelope demonstrator housing 8 p-n junctions achieves 35 nW of power under a through-thickness temperature gradient (∆ T ) of 50 Κ. Multifunctional precast building structures combining proper thermal insulation and thermal energy harvesting features possess the potential to convert waste heat into power and may contribute, in the longer term, to addressing the growing challenges associated with the urban heat-island effect.