Interface-mediated extremely low thermal conductivity of graphene aerogel

Due to the ultra-high thermal conductivity (κ) of graphene, graphene-based materials are expected to be good thermal conductors. Here, however, we uncovered extremely low κ of ultralight graphene aerogels (GAs). Although our GA (∼4 mg cm−3) is about two times heavier than air (∼1.2 mg cm−3), the κ (4.7 × 10−3−5.9 × 10−3 W m−1 K−1) at room temperature (RT) is about 80% lower than that of air (0.0257 W m−1 K−1 at 20 °C). At low temperatures, the GA's κ reaches a lower level of 2 × 10−4−4 × 10−4 W m−1 K−1. This is the lowest κ ever measured to our best knowledge. The mechanism of this extremely low κ is explored by studying the temperature variation of GA's κ, thermal diffusivity (α) and specific heat (cp) from RT to as low as 10.4 K. The uncovered small, yet positive ∂α/∂T reveals the dominant interface thermal contact resistance in thermal transport. For normal materials with thermal transport sustained by phonon-phonon scattering, ∂α/∂T always remains negative. The study of cp suggests highly disordered and amorphous structure of GAs, which also contributes to the ultralow κ. This makes the GA a very promising thermal insulation material, especially under vacuum conditions (e.g. astronautics areas).