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Reduced graphene oxide (RGO) films are promising in applications ranging from electronics to flexible sensors. Though high electrical and thermal conductivities have been reported for RGO films, existing thermal conductivity data for RGO films show large variations from 30 to 2600 W m−1 K−1. Further, there is a lack of data at low temperatures (<300 K), which is critical for the understanding of thermal transport mechanisms. In this work, a temperature‐dependent study of thermal (10–300 K) and electrical (10–3000 K) transport in annealed RGO films indicates the potential application of RGO films for sensing temperatures across an extremely wide range. The room‐temperature thermal conductivity increases significantly from 46.1 to 118.7 W m−1 K−1 with increasing annealing temperature from 1000 to 3000 K with a corresponding increase in the electrical conductivity from 5.2 to 1481.0 S cm−1. In addition, films reduced at 3000 K are promising for sensing extreme temperatures as demonstrated through the measured electrical resistivity from 10 to 3000 K. Sensors based on RGO films are advantageous over conventional temperature sensors due to the wide temperature range and flexibility. Thus, this material is useful in many applications including flexible electronics and thermal management systems.

Traditionally it has been assumed that battery thermal management systems should be designed to maintain the battery temperature around room temperature. That is not always true as Lithium-ion battery (LIB) R&D is pivoting towards the development of high energy density and fast charging batteries. Therefore, it is necessary to have a comprehensive review of thermal considerations for LIBs targeted for high energy density and fast charging, i.e., the optimal thermal condition, thermal physics (heat transport and generation) inside the battery, and thermal management strategies. As the energy density and charge rate increases, the optimal battery temperature can shift to be higher than room temperature. To improve the temperature uniformity and avoid excessive internal temperature rise, heat transfer inside the battery needs to be enhanced, and reducing the thermal contact resistance between the electrodes and separator can significantly increase the effective thermal conductivity of batteries. In the first part of the review various challenges and latest developments related to thermal transport and properties of LIBs are discussed. In the second part of the review various sources of heat generation inside LIBs and various approaches to minimizing battery heat generation are summarized. The importance of heat of mixing due to ion diffusion during fast charging is also highlighted. Finally, a summary of latest advancement on smart control of internal temperature of LIBs is discussed as depending on the ambient temperature and the optimal temperature; the battery heat needs to be retained or dissipated to elevate or avoid temperature rise. Lithium-ion battery; Optimal battery temperature; High energy density; Fast charging; Battery thermal management

Thermoelectrics operating at high temperature can cost-effectively convert waste heat and compete with other zero-carbon technologies. Among different high-temperature thermoelectrics materials, silicon nanowires possess the combined attributes of cost effectiveness and mature manufacturing infrastructures. Despite significant breakthroughs in silicon nanowires based thermoelectrics for waste heat conversion, the figure of merit (ZT) or operating temperature has remained low. Here, we report the synthesis of large-area, wafer-scale arrays of porous silicon nanowires with ultra-thin Si crystallite size of ~4 nm. Concurrent measurements of thermal conductivity (κ), electrical conductivity (σ), and Seebeck coefficient (S) on the same nanowire show a ZT of 0.71 at 700 K, which is more than ~18 times higher than bulk Si. This ZT value is more than two times higher than any nanostructured Si-based thermoelectrics reported in the literature at 700 K. Experimental data and theoretical modeling demonstrate that this work has the potential to achieve a ZT of ~1 at 1000 K.

Surface-fluorinated ultrathin anatase TiO2 nanosheets with exposed (001) crystal planes were synthesized via a relatively low temperature solvothermal route. These two-dimensional (2D) TiO2 nanosheets demonstrated higher photocatalytic activity for degrading Rhodamine B (RhB) under simulated sunlight illumination than the corresponding sample with less fluorine ions (F–) content, which indicates the positive effect of F– on the enhanced photocatalytic performance of TiO2 nanosheets. Furthermore, 2D/2D TiO2/g-C3N4 nanosheet heterojunctions were fabricated through a solvent evaporation process. The photocatalysis test showed that TiO2/g-C3N4 exhibited higher photocatalytic performance for degrading RhB under simulated solar light illumination than pure g-C3N4 and TiO2 nanosheets. Based on free radical trapping experiments, superoxide radicals (·O2–) and photoinduced holes (h+) were determined to be the predominant active species for photodegrading RhB. A direct Z-scheme charge transfer mechanism is proposed to understand the enhanced photocatalytic activity in TiO2/g-C3N4 nanosheet heterojunctions.