Due to the ultra-high thermal conductivity () of graphene, graphene-based materials are expected to be good thermal conductors. Here, however, we uncovered extremely low  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  (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  reaches a lower level of 2×10-4 4×10-4 W•m-1 •K-1. This is the lowest  ever measured to our best knowledge. The mechanism of this extremely low  is explored by studying the temperature variation of GA's , thermal diffusivity (α) and specific heat (c p) from RT to as low as 10.4 K. The uncovered small, yet positive /T reveals the dominant interface thermal contact resistance in thermal transport. For normal materials with thermal transport sustained by phononphonon scattering, /T always remains negative. The study of c p suggests highly disordered and amorphous structure of GAs, which also contributes to the ultralow . This makes the GA a very promising thermal insulation material, especially under vacuum conditions (e.g. astronautics areas).

The thermal conductivity of supported MoS2 is discovered to first decrease with thickness (<9.2 nm), then increase with thickness.

Under photon excitation, 2D materials experience cascading energy transfer from electrons to optical phonons (OPs) and acoustic phonons (APs). Despite few modeling works, it remains a long‐history open problem to distinguish the OP and AP temperatures, not to mention characterizing their energy coupling factor ( G ). Here, the temperatures of longitudinal/transverse optical (LO/TO) phonons, flexural optical (ZO) phonons, and APs are distinguished by constructing steady and nanosecond (ns) interphonon branch energy transport states and simultaneously probing them using nanosecond energy transport state‐resolved Raman spectroscopy. Δ T OP −AP is measured to take more than 30% of the Raman‐probed temperature rise. A breakthrough is made on measuring the intrinsic in‐plane thermal conductivity of suspended nm MoS 2 and MoSe 2 by completely excluding the interphonon cascading energy transfer effect, rewriting the Raman‐based thermal conductivity measurement of 2D materials. G OP↔AP for MoS 2 , MoSe 2 , and graphene paper (GP) are characterized. For MoS 2 and MoSe 2 , G OP↔AP is in the order of 10 15 and 10 14 W m −3 K −1 and G ZO↔AP is much smaller than G LO/TO↔AP . Under ns laser excitation, G OP↔AP is significantly increased, probably due to the reduced phonon scattering time by the significantly increased hot carrier population. For GP, G LO/TO↔AP is 0.549 × 10 16 W m −3 K −1 , agreeing well with the value of 0.41 × 10 16 W m −3 K −1 by first‐principles modeling.

This work uncovers that free-standing partly reduced graphene aerogel (PRGA) films in vacuum exhibit extraordinarily bolometric responses. This high performance is mainly attributed to four structure characteristics: extremely low thermal conductivity (6.0−0.6 mW•m −1 •K −1 from 295 to 10 K), high porosity, ultralow density (4 mg• cm −3 ), and abundant functional groups (resulting in tunable band gap). Under infrared radiation (peaked at 5.8−9.7 μm), the PRGA film can detect a temperature change of 0.2, 1.0, and 3.0 K of a target at 3, 25, and 54 cm distance. Even through a quartz window (transmissivity of ∼0.98 in the range of 2−4 μm), it can still successfully detect a temperature change of 0.6 and 5.8 K of a target at 3 and 28 cm distance. At room temperature, a laser power as low as 7.5 μW from a 405 nm laser and 5.9 μW from a 1550 nm laser can be detected. The detecting sensitivity to the 1550 nm laser is further increased by 3-fold when the sensor temperature was reduced from 295 K to 12 K. PRGA films are demonstrated to be a promising ultrasensitive bolometric detector, especially at low temperatures.

By removing the oxygen-containing functional groups, thermal treatment in inert gas has been widely reported to improve the hydrophobicity of carbon materials. However, this work reports a contrary phenomenon for the nitrogen-doped graphene aerogel (NGA). As the temperature of thermal treatment increases from 200 to 1000 °C, NGA becomes more and more hydrophilic and the superwetting property remains for weeks in air. To uncover this unusual phenomenon, the effect of nitrogen doping is studied through both experiment and MD simulations. The effects of air exposure and air humidity are further investigated in detail to illustrate the whole physical picture clearly. The superwetting behavior is attributed to the preferential adsorption of water molecules to the nitrogen-doped sites, which significantly inhibits airborne hydrocarbon adsorption. In combination with the excellent properties including mechanical elasticity, high light absorption, and good thermal insulation, an efficient photothermal and solar steam generation performance is demonstrated by using NGA-600 as the photothermal material, presenting a high energy conversion efficiency of 86.2% and good recycling stability.