Search

Phase change materials (PCMs) have been widely recognized as efficient solutions for thermal management across various industries, including logistics, construction, electronics, and others. Nevertheless, these materials encounter challenges such as leakage, poor thermal conductivity, and supercooling. To address these challenges, a comprehensive examination was conducted on the recent advancements pertaining to silicon‐based materials. These studies include their application as high temperature PCMs, as encapsulation matrices, and their integration as additives to enhance material properties. Aluminum–silicon (Al−Si) alloys offer a viable thermal management solution for high‐temperature applications, such as those found in car batteries. Silicon dioxide (SiO2), silicon carbide (SiC), and silicate‐based minerals have demonstrated the ability to synergistically encapsulate PCMs to prevent leakage, enhance thermal conductivity, and mitigate supercooling. However, the efficacy of these strategies in reducing supercooling varies, and a considerable number of studies have reported an exacerbation. Therefore, appropriate material selection and fine tuning for formulation are necessary. This review critically assesses silicon‐based materials as a component of PCM composite that have been developed over the years. Also, it presents an academic analysis of the selection of silicon‐based materials and the design strategy for PCM composites to optimize PCM formulations according to specific desired properties. [ABSTRACT FROM AUTHOR]

Majority of the modern electronics are made up of Si owing to a confluence of beneficial properties such as Earth-abundance, non-toxicity, light-weightedness, and versatile dopability. Yet, the thermoelectric performance of Si is not widely explored, due to the relatively high thermal conductivity of undoped Si. In this work, we devised a strategy combining light Ge alloying and B doping to simultaneously enhance the electronic properties and drastically reduce the thermal conductivity of Si. The phonon scattering brought about by Ge atoms, and optimal carrier concentration brought about by B dopant optimizes the thermal and electronic properties. Consequently, zT of 0.14 was achieved at 873 K for Si0.97Ge0.01B0.02, corresponding to 230% enhancement compared to pristine Si. The strategy reported in this work can be extended to the design of high thermoelectric performance in other Si-based compounds. [ABSTRACT FROM AUTHOR]

The presence of high crystallographic symmetry and nanoscale defects are favorable for thermoelectrics. With proper electronic structures, a highly symmetric crystal tends to possess multiple carrier channels and promote electrical conductivity without sacrificing Seebeck coefficient. In addition, nanoscale defects can effectively scatter acoustic phonons to suppress thermal conductivity. Here, it is reported that the triple doping of Cu2SnSe3 leads to a high ZT value of 1.6 at 823 K for Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3, and a decent average ZT (ZTave) value of 0.7 is also achieved for Cu1.85Ag0.15(Sn0.93Mg0.06Na0.01)Se3 from 475 to 823 K. This study reveals: 1) Ag doping on Cu sites generates numerous point defects and greatly decreases lattice thermal conductivity. 2) Doping Mg or Ga converts the monoclinic Cu2SnSe3 into a cubic structure. This symmetry enhancing leads to an increase in the effective mass from 0.8 me to 2.6 me (me, free electron mass) and the power factor from 4.3 µW cm−1 K−2 for Cu2SnSe3 to 11.6 µW cm−1 K−2. 3) Na doping creates dense dislocation arrays and nanoprecipitates, which strengthens the phonon scattering. 4) Pair distribution function analysis shows localized symmetry breakdown in the cubic Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3. This work provides a standpoint to design promising thermoelectric materials by synergistically manipulating crystal symmetry and nanoscale defects. [ABSTRACT FROM AUTHOR]

Thermoelectrics enable waste heat recovery, holding promises in relieving energy and environmental crisis. Lillianite materials have been long-term ignored due to low thermoelectric efficiency. Herein we report the discovery of superior thermoelectric performance in Pb7Bi4Se13 based lillianites, with a peak figure of merit, zT of 1.35 at 800 K and a high average zT of 0.92 (450–800 K). A unique quality factor is established to predict and evaluate thermoelectric performances. It considers both band nonparabolicity and band gaps, commonly negligible in conventional quality factors. Such appealing performance is attributed to the convergence of effectively nested conduction bands, providing a high number of valley degeneracy, and a low thermal conductivity, stemming from large lattice anharmonicity, low-frequency localized Einstein modes and the coexistence of high-density moiré fringes and nanoscale defects. This work rekindles the vision that Pb7Bi4Se13 based lillianites are promising candidates for highly efficient thermoelectric energy conversion. Lillianite materials usually have low thermoelectric efficiency due to the inherently inferior electrical properties. Here, the authors evaluate thermoelectric performances in Pb7Bi4Se13 based lillianites enabled by convergence of nested conduction bands. [ABSTRACT FROM AUTHOR]

Over the past two years, GeTe has quickly cemented its place as the best performing thermoelectric material at a medium temperature range. The key factors behind the extraordinary performance lie in its favourable electronic and thermal properties, which arise from its unique crystal structure. The slight rhombohedral distortion at temperatures below 700 K results in lower lattice thermal conductivity while maintaining high electronic properties via high level of band‐convergence. In addition, while GeTe has a cubic structure above 700 K, the local atomic disorder persists, which maintains its low thermal conductivity. To date, the understanding of the temperature‐dependent thermoelectric properties of cubic GeTe at room temperature and above is very limited. This is due to the difficulties in stabilizing cubic GeTe at low temperatures. In this work, we leverage on low level of Ti doping to stabilize cubic‐phase GeTe at room temperature and elucidate its temperature‐dependent electronic and thermal properties. Further doping with In, Cu, Sb, and Pb results in zT as high as 2 at 773 K, and high average zT of 1.4 between 300 and 800 K. [ABSTRACT FROM AUTHOR]

We present an effective approach to favorably modify the electronic structure of PbSe using Ag doping coupled with SrSe or BaSe alloying. The Ag 4d states make a contribution to in the top of the heavy hole valence band and raise its energy. The Sr and Ba atoms diminish the contribution of Pb 6s2 states and decrease the energy of the light hole valence band. This electronic structure modification increases the density‐of‐states effective mass, and strongly enhances the thermoelectric performance. Moreover, the Ag‐rich nanoscale precipitates, discordant Ag atoms, and Pb/Sr, Pb/Ba point defects in the PbSe matrix work together to reduce the lattice thermal conductivity, resulting a record high average ZTavg of around 0.86 over 400–923 K. [ABSTRACT FROM AUTHOR]

Transparent and flexible thermoelectrics has been highly sought after for future wearable devices. However, the main stumbling block to prevent its widespread adoption is the lack of p-type transparent thermoelectrics and the stringent criteria of electrical and thermal properties matching appropriately between p-legs and n-legs. This work demonstrates the fabrication of p-type PEDOT:PSS films whose optical properties, electrical conductivity, thermal conductivity, and Seebeck coefficient were engineered to perfectly match the n-type indium tin oxide (ITO) counterparts. The dense p-type PEDOT:PSS and n-type ITO thin films show a thermoelectric figure of merit of zT = 0.30 and 0.29 at 450 K, and a thermal conductivity of 0.22 and 0.32 W m−1 K−1, respectively. A flexible thermoelectric generator (TEG) module with a high transmittance of >81% in the visible wavelength range of 400–800 nm is fabricated using 10 pairs of p-type PEDOT:PSS and n-type ITO thin film legs. An ultra-high power density of 22.2 W m−2 at a temperature gradient of 80 K was observed, which is the highest power density reported for organic/hybrid-based flexible TEGs so far. Our transparent flexible thin-film p–n junction thermoelectric module with exceptionally high power generation may take a tremendous step forward towards multi-functional wearable devices. [ABSTRACT FROM AUTHOR]

This paper reports a range of effective sequential chemical processes to enhance the thermoelectric performance of conducting poly(3,4‐ethylenedioxythiophene) films doped with poly(styrene sulfonate) anions (PEDOT:PSS). The electrical conductivity of the PEDOT:PSS films was significantly increased from 0.33 to 3748 S cm−1 after a series of sequential treatments with trifluoroacetic acid (TFA) while the Seebeck coefficient and thermal conductivity were slightly reduced from 17.5 ± 1.2 to 16.0 ± 1.1 μV K−1 and 0.537 to 0.415 W m–1 K−1 for the pristine film and treated film, respectively, leading to a significant improvement in power factor up to 97.1 ± 5.4 μW m–1 K−2. More importantly, around 80% of the electrical conductivity and Seebeck coefficient was retained after 20 days for these TFA‐treated PEDOT:PSS films, revealing the potential for real thermoelectric applications. © 2019 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: Sb‐doped and GeTe‐alloyed n‐type thermoelectric materials that show an excellent figure of merit ZT in the intermediate temperature range (400–800 K) are reported. The synergistic effect of favorable changes to the band structure resulting in high Seebeck coefficient and enhanced phonon scattering by point defects and nanoscale precipitates resulting in reduction of thermal conductivity are demonstrated. The samples can be tuned as single‐phase solid solution (SS) or two‐phase system with nanoscale precipitates (Nano) based on the annealing processes. The GeTe alloying results in band structure modification by widening the bandgap and increasing the density‐of‐states effective mass of PbTe, resulting in significantly enhanced Seebeck coefficients. The nanoscale precipitates can improve the power factor in the low temperature range and further reduce the lattice thermal conductivity (κlat). Specifically, the Seebeck coefficient of Pb0.988Sb0.012Te–13%GeTe–Nano approaches −280 µV K−1 at 673 K with a low κlat of 0.56 W m−1 K−1 at 573 K. Consequently, a peak ZT value of 1.38 is achieved at 623 K. Moreover, a high average ZTavg value of ≈1.04 is obtained in the temperature range from 300 to 773 K for n‐type Pb0.988Sb0.012Te–13%GeTe–Nano. [ABSTRACT FROM AUTHOR]

0D transition metal phosphides (TMPs) nanocrystals (NCs)-2D ultrathin black phosphorus (BP) heterostructure (Ni2P@BP) have been synthesized via a facile sonication-assisted exfoliation followed by a solvothermal process. Compared with the bare BP, the specially designed Ni2P@BP architecture can enhance the electrical conductivity (from 2.12 × 102 to 6.25 × 104 S m-1), tune the charge carrier concentration (from 1.25 × 1017 to 1.37 × 1020 cm-3), and reduce the thermal conductivity (from 44.5 to 7.69 W m-1 K-1) at 300 K, which can be considered for multiple applications. As a result, the Ni2P@BP exhibits excellent Li storage properties and high hydrogen evolution reaction electrocatalytic activities. The Ni2P@BP shows improved Li diffusion kinetics (e.g., the Li ions diffusion coefficient increases from 1.14 × 10-14 cm2 s-1 for pure BP nanosheets to 8.02 × 10-13 cm2 s-1 for Ni2P@BP). In addition, the Ni2P@BP electrode sustains hydrogen production with almost unchanged activity over 3000 cycles, which indicates its good chemical stability when operating under strong reducing environment. [ABSTRACT FROM AUTHOR]

The presence of high crystallographic symmetry and nanoscale defects are favorable for thermoelectrics. With proper electronic structures, a highly symmetric crystal tends to possess multiple carrier channels and promote electrical conductivity without sacrificing Seebeck coefficient. In addition, nanoscale defects can effectively scatter acoustic phonons to suppress thermal conductivity. Here, it is reported that the triple doping of Cu2SnSe3 leads to a high ZT value of 1.6 at 823 K for Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3, and a decent average ZT (ZTave) value of 0.7 is also achieved for Cu1.85Ag0.15(Sn0.93Mg0.06Na0.01)Se3 from 475 to 823 K. This study reveals: 1) Ag doping on Cu sites generates numerous point defects and greatly decreases lattice thermal conductivity. 2) Doping Mg or Ga converts the monoclinic Cu2SnSe3 into a cubic structure. This symmetry enhancing leads to an increase in the effective mass from 0.8 me to 2.6 me (me, free electron mass) and the power factor from 4.3 µW cm−1 K−2 for Cu2SnSe3 to 11.6 µW cm−1 K−2. 3) Na doping creates dense dislocation arrays and nanoprecipitates, which strengthens the phonon scattering. 4) Pair distribution function analysis shows localized symmetry breakdown in the cubic Cu1.85Ag0.15(Sn0.88Ga0.1Na0.02)Se3. This work provides a standpoint to design promising thermoelectric materials by synergistically manipulating crystal symmetry and nanoscale defects. [ABSTRACT FROM AUTHOR]