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Two-dimensional (2D) thermoelectric (TE) materials have been widely developed; however, some 2D materials exhibit isotropic phonon, electron transport properties, and poor TE performance, which limit their application scope. Thus, exploring excellent anisotropic and ultrahigh-performance TE materials are very warranted. Herein, we first investigate the phonon thermal and TE properties of a novel 2D-connectivity ternary compound named Ga₂I₂S₂ . This paper comprehensively studies the phonon dispersion, phonon anharmonicity, lattice thermal conductivity, electronic structure, carrier mobility, Seebeck coefficient, electrical conductivity, and the dimensionless figure of merit (ZT) versus carrier concentration for 2D Ga₂I₂S₂ . We conclude that the in-plane lattice thermal conductivities of Ga₂I₂S₂ at room temperature (300 K) are found to be 1.55 W mK⁻¹ in the X-axis direction (xx-direction) and 3.82 W mK⁻¹ in the Y-axis direction (yy-direction), which means its anisotropy ratio reaches 1.46. Simultaneously, the TE performance of p-type and n-type doping 2D Ga₂I₂S₂ also shows significant anisotropy, giving rise to the ZT peak values of p-type doping in xx- and yy-directions being 0.81 and 1.99, respectively, and those of n-type doping reach ultrahigh values of 7.12 and 2.89 at 300 K, which are obviously higher than the reported values for p-type and n-type doping ternary compound Sn₂BiX (ZT∼ 1.70 and ∼2.45 at 300 K) (2020 Nano Energy 67 104283). This work demonstrates that 2D Ga₂I₂S₂ has high anisotropic TE conversion efficiency and can also be used as a new potential room-temperature TE material.

The heat conduction and thermal conductivity for methane hydrate are simulated from equilibrium molecular dynamics. The thermal conductivity and temperature dependence trend agree well with the experimental results. The nonmonotonic temperature dependence is attributed to the phonon inelastic scattering at higher temperature and to the confinement of the optic phonon modes and low frequency phonons at low temperature. The thermal conductivity scales proportionally with the van der Waals interaction strength. The conversion of a crystal-like nature into an amorphous one occurs at higher strength. Both the temperature dependence and interaction strength dependence are explained by phonon inelastic scattering.

To improve the thermal conductivity of polymeric composites, the numerous interfacial thermal resistance (ITR) inside is usually considered as a bottle neck, but the direct measurement of the ITR is hardly reported. In this paper, a sandwich structure which consists of transducer/high density polyethylene (HDPE)/sapphire is prepared to study the interface characteristics. Then, the ITRs between HDPE and sapphire of two samples with different HDPE thickness values are measured by time-domain thermoreflectance (TDTR) method and the results are ~ 2 × 10−7 m2KW−1. Furthermore, a model is used to evaluate the importance of ITR for the thermal conductivity of composites. The model's analysis indicates that reducing the ITR is an effective way of improving the thermal conductivity of composites. These results will provide valuable guidance for the design and manufacture of polymer-based thermally conductive materials.

Heat management at nanoscale is a critical issue across many areas of science and engineering, where the size effect of thermal properties plays an important role. We measure the transient thermoreflectance signals of thin metal films with thicknesses from 50 to 200nm by using the femtosecond laser pump and probe method, and the experimental data are combined with the parabolic two-step model to enable us to measure thermal conductivity of the thin metal films. The measurement results of Ni and Al films show that, in the thickness range from tens to hundreds of nanometer, the thermal conductivity increases with the increasing thicknesses of the films, which agrees well with the previous conclusions.

We develop a solar simulator composed of multiple xenon arc lamps combined with a faceted paraboloidal dish concentrator to drive a Stirling engine in our laboratory for all-weather indoor testing. Experiments and numerical analysis are performed to determine the radiation flux and temperature distributions on the solar receiver surface. Based on the theoretical results, we present a receiver design for a solar Stirling engine with involute tubes closely conforming to the imaginary hemisphere to obtain a substantially uniform temperature field and a high solar-thermal efficiency of 67.1%.