Optimizing Waste Heat Conversion: Integrating Phase-Change Material Heatsinks and Wind Speed Dynamics to Enhance Flexible Thermoelectric Generator Efficiency.

Flexible thermoelectric generators (FTEGs) have garnered significant attention for their potential in harnessing waste heat energy from various sources. To optimize their efficiency, FTEGs require efficient and adaptable heatsinks. In this study, we propose a cost-effective solution by integrating phase-change materials into FTEG heatsinks. We developed and tested three flexible phase-change material thicknesses (4 mm, 7 mm, and 10 mm), focusing on preventing leaks during operation. Additionally, we investigated the impact of wind speed on the output performance of FTEGs with a flexible phase-change material heatsink. The results indicate that the appropriate flexible phase-change material thickness, when integrated with considerations for wind speed, demonstrates remarkable heat-absorbing capabilities at phase-change temperatures. This integration enables substantial temperature differentials across the FTEG modules. Specifically, the FTEG equipped with a 10 mm thick flexible phase-change material heatsink achieved a power density more than four times higher when the wind speed was at 1 m/s compared to no wind speed. This outcome suggests that integrating phase-change material heatsinks with relatively low wind speeds can significantly enhance flexible thermoelectric generator efficiency. Finally, we present a practical application wherein the FTEG, integrated with the flexible phase-change material heatsink, efficiently converts waste heat from a circular hot pipe into electricity, serving as a viable power source for smartphone devices. This work opens exciting possibilities for the future integration of flexible thermoelectric modules with flexible phase-change material heatsinks, offering a promising avenue for converting thermal waste heat into usable electricity.

First-principles study of 2H-Mo2C-based MXenes under biaxial strain as Li-battery anodes.

MXenes, a family of superior 2D materials, have been intensively investigated because they have many promising properties, particularly high-performance energy storage and high flexibility. To approach the expected critical benchmarks of such materials, the strain dependence of the atomic structure is widely considered for tuning the related properties. In this work, by means of density functional theory, we demonstrate the potential application of the strained 2H phase of Mo2C-based MXenes (Mo2C and Mo2CO2) as anode materials for lithium-ion batteries (LIBs). Adsorption and diffusion of Li on the surfaces of both materials and the impact of biaxial strain (εb) in the range of -4% to 4% are insightfully investigated. The lowest adsorption energy of Mo2C is -0.96 eV, and that of Mo2CO2 is -3.13 eV at εb = 0%. The diffusion of Li ions, considering the pathway between the first two most favorable adsorption sites, reveals that the biaxial strain refinement under compressive strain decreases the energy barrier, but the induction of tensile strain increases it in both MXenes. The ranges of the energy barriers of Li-ion adsorption on the surfaces of Mo2C and Mo2CO2 are 31-57 meV and 177-229 meV, respectively. Interestingly, the storage capacity of Li can reach three layers corresponding to a comparably high theoretical capacity of 788.61 mA h g-1 for Mo2C and 681.64 mA h g-1 for Mo2CO2. The atomic configurations are stable, as verified by the negative adsorption energy as well as the slightly distorted structures, by using ab initio molecular dynamics (AIMD) simulations at 400 K. Moreover, average open circuit voltages (OCVs) of 0.35 V and 0.63 V (at εb = 0%) are reported for Mo2C and Mo2CO2, respectively. Furthermore, the tensile strain results in an increase in the OCVs, while compression has the opposite effect. These computational results provide some basic information on the behaviors of Li-ion adsorption and diffusion on Mo2C-based MXenes upon tuning biaxial strain. They also give a guideline on what conditions are appropriate for practically implementing these MXenes as electrode materials in LIBs.

Thickness Dependence of Thermoelectric Properties and Maximum Output Power of Single Planar Sb2Te3 Films.

P-type Sb2Te3 films with different thicknesses were deposited on polyimide substrates via heat treatment-assisted DC magnetron sputtering. The correlations between the thickness variance and the structure, dislocation density, surface morphology, thermoelectric properties and output power are investigated. As a result, it is clear that the film thickness and the heat treatment process during growth are related to the diffusion of deposited atoms on the substrate surface, leading to imperfection defects inside the films. The imperfections inside the films are affected by their properties. This work also presents the thermoelectric efficiency of a planar single leg of the deposited films with various thicknesses. The maximum power factor is 2.73 mW/mK2 obtained with a film thickness of 9.0 µm and an applied temperature of 100 °C. Planar Sb2Te3 produced a maximum output power of 0.032 µW for a temperature difference of 58 K.

Investigation of Radiation Effect on Structural and Optical Properties of GaAs under High-Energy Electron Irradiation.

A systematic investigation of the changes in structural and optical properties of a semi-insulating GaAs (001) wafer under high-energy electron irradiation is presented in this study. GaAs wafers were exposed to high-energy electron beams under different energies of 10, 15, and 20 MeV for absorbed doses ranging from 0-2.0 MGy. The study showed high-energy electron bombardments caused roughening on the surface of the irradiated GaAs samples. At the maximum delivered energy of 20 MeV electrons, the observed root mean square (RMS) roughness increased from 5.993 (0.0 MGy) to 14.944 nm (2.0 MGy). The increased RMS roughness with radiation doses was consistent with an increased hole size of incident electrons on the GaAs surface from 0.015 (0.5 MGy) to 0.066 nm (2.0 MGy) at 20 MeV electrons. Interestingly, roughness on the surface of irradiated GaAs samples affected an increase in material wettability. The study also observed the changes in bandgap energy of GaAs samples after irradiation with 10, 15, and 20 MeV electrons. The band gap energy was found in the 1.364 to 1.397 eV range, and the observed intense UV-VIS spectra were higher than in non-irradiated samples. The results revealed an increase of light absorption in irradiated GaAs samples to be higher than in original-based samples.