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.

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.

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.

This work reports on the discovery of a high thermal conductivity (κ) switch-on phenomenon in high purity graphene paper (GP) when its temperature is reduced from room temperature down to 10 K. The κ after switch-on (1732 to 3013 W m −1 K −1 ) is 4-8 times that before switch-on. The triggering temperature is 245-260 K. The switch-on behavior is attributed to the thermal expansion mismatch between pure graphene flakes and impurity-embedded flakes. This is confirmed by the switch behavior of the temperature coefficient of resistance. Before switch-on, the interactions between pure graphene flakes and surrounding impurity-embedded flakes efficiently suppress phonon transport in GP. After switch-on, the structure separation frees the pure graphene flakes from the impurity-embedded neighbors, leading to a several-fold κ increase. The measured κ before and after switch-on is consistent with the literature reported κ values of supported and suspended graphene. By conducting comparison studies with pyrolytic graphite, graphene oxide paper and partly reduced graphene paper, the whole physical picture is illustrated clearly. The thermal expansion induced switch-on is feasible only for high purity GP materials. This finding points out a novel way to switch on/off the thermal conductivity of graphene paper based on substrate-phonon scattering.

Sluggish transport kinetics and unstable electrode-electrolyte interface are the main obstacles that greatly impair the electrochemical performance of solid-state Zn metal batteries. Herein, the concept of multifunctional MXene bonded transport network-embedded poly(vinylidene fluoride co-hexafluoropropylene)/Zn(OTf ) 2 solid polymer electrolyte (PH/MXene SPE) is proposed as "all-in-one" strategy for designing robust SPE. In order to uncover the mechanism of such rational designed SPE on regulating the ion transport, as well as the interphase chemistry and Zn deposition, comprehensive research including density functional theory calculation, simulation, and multiple characterization techniques are carried out. As the results indicate, the formation of hydrogen bond network between the MXene nanofiller and PH polymer benefits fast and homogeneous ion transport. Then, the in situ formation of stable organic/inorganic hybrid interphase is capable to ensure the efficient interfacial transport kinetics and uniform Zn deposition. When such PH/ MXene SPE is applied, ultrastable Zn plating/stripping behavior with small polarization voltage can be realized. In addi, solid-state Zn/VO 2 batteries with significantly improved rate performance and cyclic stability also can be demonstrated. The unique strategy proposed in this study offer a new insight into SPE design and the development of high-performance solid-state Zn metal batteries.

Due to its intriguing thermal and electrical properties, graphene has been widely studied for potential applications in sensor and energy devices. However, the reported value for its thermal conductivity spans from dozens to thousands of W m(-1) K(-1) due to different levels of alternations and defects in graphene samples. In this work, the thermal diffusivity of suspended four-layered graphene foam (GF) is characterized from room temperature (RT) down to 17 K. For the first time, we identify the defect level in graphene by evaluating the inverse of thermal diffusivity (termed "thermal reffusivity": Θ) at the 0 K limit. By using the Debye model of Θ = Θ0 + C× e(-θ/2T) and fitting the Θ-T curve to the point of T = 0 K, we identify the defect level (Θ0) and determine the Debye temperature of graphene. Θ0 is found to be 1878 s m(-2) for the studied GF and 43-112 s m(-2) for three highly crystalline graphite materials. This uncovers a 16-43-fold higher defect level in GF than that in pyrolytic graphite. In GF, the phonon mean free path solely induced by defects and boundary scattering is determined as 166 nm. The Debye temperature of graphene is determined to be 1813 K, which is very close to the average theoretical Debye temperature (1911 K) of the three acoustic phonon modes in graphene. By subtracting the defect effect, we report the ideal thermal diffusivity and conductivity (κideal) of graphene presented in the 3D foam structure in the range of 33-299 K. Detailed physics based on chemical composition and structure analysis are given to explain the κideal-T profile by comparing with those reported for suspended graphene.

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.