Boosting Thermoelectric Performance via Weakening Carrier-Phonon Coupling in BiCuSeO-Graphene Composites.

BiCuSeO is a promising oxygen-containing thermoelectric material due to its intrinsically low lattice thermal conductivity and excellent service stability. However, the low electrical conductivity limits its thermoelectric performance. Aliovalent element doping can significantly improve their carrier concentration, but it may also impact carrier mobility and thermal transport properties. Considering the influence of graphene on carrier-phonon decoupling, Bi0.88 Pb0.06 Ca0.06 CuSeO (BPCCSO)-graphene composites are designed. For further practical application, a rapid preparation method is employed, taking less than 1 h, which combines self-propagating high-temperature synthesis with spark plasma sintering. The incorporation of graphene simultaneously optimizes the electrical properties and thermal conductivity, yielding a high ratio of weighted mobility to lattice thermal conductivity (144 at 300 K and 95 at 923 K). Ultimately, BPCCSO-graphene composites achieve exceptional thermoelectric performance with a ZT value of 1.6 at 923 K, bringing a ≈40% improvement over BPCCSO without graphene. This work further promotes the practical application of BiCuSeO-based materials and this facile and effective strategy can also be extended to other thermoelectric systems.

Compositing effects for high thermoelectric performance of Cu2Se-based materials.

Thermoelectric materials can realize direct conversion between heat and electricity, showing excellent potential for waste heat recovery. Cu2Se is a typical superionic conductor thermoelectric material having extraordinary ZT values, but its superionic feature causes poor service stability and low mobility. Here, we reported a fast preparation method of self-propagating high-temperature synthesis to realize in situ compositing of BiCuSeO and Cu2Se to optimize the service stability. Additionally, using the interface design by introducing graphene in these composites, the carrier mobility could be obviously enhanced, and the strong phonon scatterings could lead to lower lattice thermal conductivity. Ultimately, the Cu2Se-BiCuSeO-graphene composites presented excellent thermoelectric properties with a ZTmax value of ~2.82 at 1000 K and a ZTave value of ~1.73 from 473 K to 1000 K. This work provides a facile and effective strategy to largely improve the performance of Cu2Se-based thermoelectric materials, which could be further adopted in other thermoelectric systems.

Robust, Flexible Thermoelectric Film for Energy Harvesting by a Simple and Eco-Friendly Method.

As for the self-supporting composite films, it is significant to develop a structural design that allows for excellent flexibility while reducing the negative effect on thermoelectric (TE) properties. Herein, a robust, flexible TE film was fabricated by in situ chemical transformation and vacuum-assisted filtration without any organic solvents involved. The performance of the films was further optimized by adjusting the Ag/Te ratio and post-treatment methods. Owing to the semi-interpenetrating nanonetwork structure formed by AgxTe nanowires and bacterial cellulose, the obtained TE film displayed a high tensile strength of ∼78.4 MPa and a high power factor of 48.9 µW m-1 K-2 at room temperature. A slight electrical conductivity decrement of the TE film in flexible test (∼2% after 1000 bending cycles) indicates an excellent flexibility. Finally, a TE bracelet was assembled to harvest body heat energy, and a steady current of ∼2.7 µA was generated when worn on the wrist indoors. This work provides a reference for the structural design and practical application of flexible TE films.

High Thermoelectric Performance of AgSb1-xPbxSe2 Prepared by Fast Nonequilibrium Synthesis.

AgSbSe2 is a typical member of cubic I-V-VI2 semiconductors, which are known for their extremely low lattice thermal conductivity (κl). However, the low electrical conductivity of AgSbSe2, below ∼10 S cm-1 at room temperature, has hindered its thermoelectric performance. In this work, single-phase AgSbSe2 bulk samples with much higher electrical conductivity were synthesized via self-propagating high-temperature synthesis (SHS) combined with spark plasma sintering (SPS) for the first time. Pb doping through the nonequilibrium process further increases the electrical conductivity to >100 S cm-1. Furthermore, continuously increased effective mass md* can be achieved upon Pb doping because of the multiple degenerate valence bands of AgSbSe2 and the energy-filtering effect induced by in situ-formed nanodots. The simultaneous enhancement of both the electrical conductivity and Seebeck coefficient contributes to an unprecedentedly high average power factor of 6.75 µW cm-1 K-2. Meanwhile, the introduced dense grain boundaries and point defects enhance the phonon scattering and consequently suppress κl, yielding a high ZT value of 1.2 at 723 K in AgSb0.94Pb0.06Se2. This study opens a new avenue for rapid, low-cost, large-scale production of AgSbSe2-based materials and demonstrates that Pb-doped AgSbSe2 prepared via the SHS-SPS method is a promising candidate for thermoelectric applications.

Flexible PANI/SWCNT thermoelectric films with ultrahigh electrical conductivity.

The effects of polyaniline (PANI) with different polymerization times on the film-forming and thermoelectric properties as well as on the performance of SWCNTs/PANI composites were systematically investigated in this study. It was found that the film-forming and flexibility of PANI films improved with the increase in polymerization time. We showed that a super high conductivity of ∼4000 S cm-1 can be achieved for the SWCNTs/PANI composite film, which is the highest value for the SWCNTs/PANI system at present. Both the electrical conductivity and power factor increase by an order of magnitude than that of pure PANI films and far exceed the theoretical value of the mixture model. These results suggest that the sufficiently continuous and ordered regions on the interlayer between the filler and matrix are key to improve the electrical conductivity of composites. Finally, the maximum PF reaches 100 µW m-1 K-2 at 410 K for the 0.6CNT/PANI5h. Furthermore, it is found that the composite films have excellent environmental and structural stability. Our results can deepen the understanding of organic-inorganic thermoelectric composite systems and facilitate the practical application of flexible and wearable thermoelectric materials.

Bio-inspired spider-web-like membranes with a hierarchical structure for high performance lithium/sodium ion battery electrodes: the case of 3D freestanding and binder-free bismuth/CNF anodes.

High gravimetric energy density and volumetric energy density energy storage devices are highly desirable due to the rapid development of electric vehicles, and portable and wearable electronic equipment. Electrospinning is a promising technology for preparing freestanding electrodes with high gravimetric and volumetric energy density. However, the energy density of the traditional electrospun electrodes is restricted by the low mass loading of active materials (e.g. 20%-30 wt%). Herein, a biomimetic strategy inspired by the phenomenon of the sticky spider web is demonstrated as a high performance anode, which simultaneously improves the gravimetric and volumetric energy density. Freestanding carbon nanofiber (CNF) membranes containing over 50 wt% of bismuth were prepared by electrospinning and subsequent thermal treatment. Membranes consisting of CNF network structures bonded tightly with active Bi cluster materials, resulting in excellent mechanical protection and a fast charge transport path, which are difficult to achieve simultaneously. The composite membrane delivers high reversible capacity (483 mA h g-1 at 100 mA g-1 after 200 cycles) and high rate performance (242 mA h g-1 at 1 A g-1) as a lithium-ion battery anode. For use as a sodium ion battery, the composite membrane also shows a high reversible specific capacity of 346 mA h g-1 and outstanding cycling performance (186 mA h g-1 at 50 mA g-1 after 100 cycles). This work offers a simple, low cost and eco-friendly method for fabricating free-standing and binder-free composite electrodes with high loading used in LIBs and SIBs.

High-Performance Li-Ion Capacitor Based on an Activated Carbon Cathode and Well-Dispersed Ultrafine TiO2 Nanoparticles Embedded in Mesoporous Carbon Nanofibers Anode.

A novel Li-ion capacitor based on an activated carbon cathode and a well-dispersed ultrafine TiO2 nanoparticles embedded in mesoporous carbon nanofibers (TiO2@PCNFs) anode was reported. A series of TiO2@PCNFs anode materials were prepared via a scalable electrospinning method followed by carbonization and a postetching method. The size of TiO2 nanoparticles and the mesoporous structure of the TiO2@PCNFs were tuned by varying amounts of tetraethyl orthosilicate (TEOS) to increase the energy density and power density of the LIC significantly. Such a subtle designed LIC displayed a high energy density of 67.4 Wh kg-1 at a power density of 75 W kg-1. Meanwhile, even when the power density was increased to 5 kW kg-1, the energy density can still maintain 27.5 Wh kg-1. Moreover, the LIC displayed a high capacitance retention of 80.5% after 10000 cycles at 10 A g-1. The outstanding electrochemical performance can be contributed to the synergistic effect of the well-dispersed ultrafine TiO2 nanoparticles, the abundant mesoporous structure, and the conductive carbon networks.

Enhanced thermoelectric performance of In2O3-based ceramics via Nanostructuring and Point Defect Engineering.

The issue of how to improve the thermoelectric figure of merit (ZT) in oxide semiconductors has been challenging for more than 20 years. In this work, we report an effective path to substantial reduction in thermal conductivity and increment in carrier concentration, and thus a remarkable enhancement in the ZT value is achieved. The ZT value of In2O3 system was enhanced 4-fold by nanostructuing (nano-grains and nano-inclusions) and point defect engineering. The introduction of point defects in In2O3 results in a glass-like thermal conductivity. The lattice thermal conductivity could be reduced by 60%, and extraordinary low lattice thermal conductivity (1.2 W m(-1) K(-1) @ 973 K) below the amorphous limit was achieved. Our work paves a path for enhancing the ZT in oxides by both the nanosturcturing and the point defect engineering for better phonon-glasses and electron-crystal (PGEC) materials.

Enhanced thermoelectric properties of Pb-doped BiCuSeO ceramics.

A high-performance thermoelectric oxyselenide BiCuSeO ceramic with ZT > 1.1 at 823 K and higher average ZT value (ZTave ≈0.8) is obtained. The heavy doping element and nanostructures can effectively tune its electronic structure, hole concentration, and thermal conductivity, resulting in substantially enhanced mobility, power factor, and thus ZT value. This work provides a path to high-performance thermoelectric ceramics.