High-energy B-O bonds enable the phenolic aerogel with enhanced thermal stability and low thermal conductivity

Phenolic aerogels have addressed considerate application in fabricating lightweight ablative materials owing to their excellent characteristics of large surface area, low bulk density, and low thermal conductivity . However, unsatisfactory thermal stability still limits their extensive applications. To enhance the thermal stability, we reported a facile co-precursor strategy to prepare boron-modified phenolic aerogels, through sol–gel polymerization of phenylboronic acid and phenolic resin. The thermal stability of hybrid aerogels is remarkably enhanced, achieving a char yield of up to 64.16 % at 850 ℃ due to the much higher bonding energy of B-O bonds. The phenyl-borates structure gradually transferred into B 2 O 3 , effectively fixing the oxygen content and reducing the carbon loss during the carbonization process. Moreover, the in-situ formed phenyl-borates structure contributes to forming a denser network, which affords the hybrid aerogels with diverse properties: low density (0.31–0.34 g/cm 3 ), a hierarchical micro- meso -macro porous structure with small particle size (28.42–48.58 nm), promoted compressive strength (20.65–28.46 MPa), and excellent insulation performance (0.0406–0.0564 W/(m•k)). These integrated superiorities enable the boron-modified phenolic aerogels to perform effectively in thermal insulation fields, especially for aerospace related industry.