Although organic and composite thermoelectric (TE) materials have witnessed explosive developments in the past five years, the research of flexible TE devices is rather limited. In particular, their ...assembly strategies and device performance reported in the literature cannot be directly compared, due to a variety of deviances including p‐ and n‐type component materials, shape and dimensions of p‐n flexible films, and applied temperature gradient (ΔT). Here, three types of assembly strategies for flexible TE devices, that is, serial, folding, and stacking, are compared by fixing the corresponding experimental parameters. Furthermore, a convenient and general method to evaluate the flexible device performance (FDP) is put forward, that is, FDP = PmaxmΔTN, where the maximum output power (Pmax) is divided by product mass (m), ΔT, and pair number of p‐n couples (N). The FDPs for the present serial, folding, and stacking devices are 11.13, 8.87, and 0.05 nW g−1 K−1, respectively, confirming that the serial configuration is the best among the three strategies for flexible device fabrication. The preliminary evaluation method proposed herein will pave the way for a design strategy of flexible TE devices and speed up their applications in waste‐heat harvesting, e‐skin, wearable electronics, etc.
Three assembly strategies to fabricate flexible thermoelectric devices, including serial, folding and stacking, are compared. Furthermore, a convenient and general method to evaluate device performance FDP = PmaxmΔTN is proposed. The FDP for serial, folding and stacking devices are 11.13, 8.87 and 0.05 nW g−1 K−1, respectively, confirming that the thermoelectric capability follows the sequence of serial > folding ≫ stacking.
2D hierarchically porous carbon (2D-HPC) nanosheets with unique advantages are highly desired as host materials for lithium sulfur (Li–S) batteries and other energy storage devices. Herein, we ...propose a self-template and organic solvent-free approach to synthesize nanosheets of monoclinic ZIF-8 at room temperature from which 2D-HPC nanosheets (ZIF-8 nanosheets carbon denoted as ZIF-8-NS-C) are derived to be an efficient sulfur immobilizer for Li–S batteries for the first time. The anisotropic nanosheets are believed to relate to the symmetry of the monoclinic structure. The 2D ZIF-8-NS-C nanosheets with embedded hierarchical pores construct an effective conductive network through “plane-to-plane” modes to endow superior electron transfer and fast electrochemical kinetics. Moreover, the nitrogen-rich feature of ZIF-8-NS-C can increase the affinity/interaction of carbon host with lithium polysulfides, favoring the cyclic performance. The sulfur/ZIF-8-NS-C (S/ZIF-8-NS-C) cathode shows a superior rate capability with high capacities of 1226 mA h g–1 at 0.2 C and 785 mA h g–1 at 2 C, and a sustainable cycling stability with a capacity attenuation of 0.12% per cycle at 0.5 C for 300 cycles. The approach proposed here pioneers the controllable design of MOF-based structures to inspire the exploration of more variable MOF-derived porous materials for energy storage applications.
Despite the significant progress in thermoelectric composites in the last five years, examining the existing main body of publications shows the scarcity of composite systems and limited preparation ...strategies. Metal-organic frameworks (MOFs) have been extensively studied and have wide applications, however, MOF-related thermoelectric composites have been seldom reported mainly due to their poor electrical conductivity. In this work, we propose a conceptual strategy, in situ growing reaction and subsequent annealing, to achieve zeolitic imidazolate framework 67/carbon nanotube (ZIF-67@CNT) composites with a unique microstructure of MOFs growing on CNT surfaces. The ZIF-67@CNT composites display outstanding and tunable thermoelectric properties. Annealing plays an important role in the composite morphology, structure and thermoelectric performance. Both the electrical conductivity (825.7 ± 12.0 S cm−1) and the figure of merit (ZT = ∼0.02) at room temperature are the highest in the experimental data reported so far for MOF-related materials, and even comparable to the corresponding theoretical values. The results inspire a new insight into MOF-related thermoelectric composites, which should be considered for future design strategies for novel high-performance thermoelectric composites.
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Flexible thin films of poly(nickel‐ethylenetetrathiolate) prepared by an electrochemical method display promising n‐type thermoelectric properties with the highest ZT value up to 0.3 at room ...temperature. Coexistence of high electrical conductivity and high Seebeck coefficient in this coordination polymer is attributed to its degenerate narrow‐bandgap semiconductor behavior.
Organic and composite thermoelectric (TE) materials have witnessed explosive developments in recent years. Design strategy of their flexible devices is vital to achieve high performance and suit ...various application environments. Here, we propose a design strategy of annular flexible TE devices with integrated-module architecture, where the independent modules made up of alternatively connected p-n couples are connected in series, and then rounded head-to-tail into annular configuration. The achieved devices can not only save plenty of space owing to their highly integrated structure design, but also be directly mounted on cylindrical objects (like pipes) to suit versatile applications. More importantly, the annular TE devices display excellent performances, superior to most previous work and the traditional serial single-layer film structure. For example, the annular device with eight modules consisting of three p-n couples reveals an output power of 12.37 μW at a temperature gradient of 18 K, much higher than that of the corresponding single-layer film structure (1.74 μW). The integration process is simple and easy to scale up. This architecture design strategy will greatly speed up the TE applications and benefit the research of organic and composite TE materials.
Solution processability and flexibility still remain major challenges for many thermoelectric (TE) materials, including bismuth telluride (Bi2Te3), a typical and commercially available TE material. ...Here, we report a new solution‐processed method to prepare a flexible film of a Bi2Te3/single‐walled carbon nanotube (SWCNT) hybrid, where the dissolved Bi2Te3 ion precursors are mixed with dispersed SWCNTs in solution and recrystallized on the SWCNT surfaces to form a “cement–rebar”‐like architecture. The hybrid film shows an n‐type characteristic, with a stable Seebeck coefficient of −100.00 ± 1.69 μV K−1 in air. Furthermore, an extremely low in‐plane thermal conductivity of ∼0.33 W m−1 K−1 is achieved at 300 K, and the figure of merit (ZT) reaches 0.47 ± 0.02. In addition, the TE performance is independent of mechanical bending. The unique “cement–rebar”‐like architecture is believed to be responsible for the excellent TE performances and the high flexibility. The results provide a new avenue for the fabrication of solution‐processable and flexible TE hybrid films and will speed up the applications of flexible electronics and energy conversion.
A solution‐processed Bi2Te3/SWCNT (2 wt%) hybrid film shows a high figure of merit (ZT) of ∼0.47 with an extremely low thermal conductivity of ∼0.33 W m−1 K−1 at 300 K and the hybrid film shows excellent flexibility and high stability, showing promising potential for versatile applications, especially flexible and wearable electronics.
LiFexMn2-xO4 (x=0.0, 0.1 and 0.2) with superior rate and cycling performance is synthesized using a sol – gel method by combining citric acid and glucose as the chelating agent. For the first time Fe ...is found to basically occupy the 16d site. Fe doping decreases the occupancies of Mn at the 8a site considerably, and reduces the variations of the lattice volume before and after charge significantly, and suppresses the formation of the lower valence manganese surface phases. The structure - related factors other than the conventional morphology and size lead to the drastically enhanced performance of the Fe - doped samples. The combination of the decreased occupancies of Mn on the 8a site, and the only occupation of Fe on the 16d site, and the suppression of the surface phases of manganese ions with the lower valences and the alleviation of the Jahn - Teller effect due to the partial replacement of Mn3+ by Fe3+ result in both the improved electronic and ionic conductivities, and thus the drastically enhanced performance. The capacity of 66 mAh g−1 for x = 0.2 is delivered for 300C discharge with 1C charge. The capacity retentions after 1500 cycles for 100C discharge and 10C charge at room temperature (RT) and 60°C are 90% and 83%, respectively. The present study opens a feasible way to obtain the high performance manganese spinel cathode by controlling the lattice site occupation of an alien element and manganese and the formation of low valence manganese surface phases.
Oxygen deficiencies are well recognized to have a detrimental effect on the performance of spinel LiMn
2
O
4-δ
as the cathode for non-aqueous systems, whereas the influences have not been explored ...for aqueous systems yet. Here, we successfully introduce oxygen deficiencies into LiMn
2
O
4-δ
by calcination of oxygen deficiency-free LiMn
2
O
4
at 850 °C for 2 h followed by quenching in air. LiMn
2
O
4-δ
primary particles show the octahedral shape, the sizes of about 400 nm, and the larger lattice constant of 8.240 Å, in contrast with the irregular shapes, the sizes of about 100 nm, and the lattice constant of 8.231 Å. In the non-aqueous system, the performances for LiMn
2
O
4-δ
are inferior compared to LiMn
2
O
4,
as reported previously. However, both LiMn
2
O
4-δ
||polyimide and LiMn
2
O
4
||polyimide aqueous full cells exhibit the discharge capacity of about 105 mAh g
−1
at 100 mA g
−1
and the capacity retentions of 87% and 60% after 100 cycles. The plateau of H
2
O decomposition observed at about 1.85 V for LiMn
2
O
4
leads to much poorer performance which is absent for LiMn
2
O
4-δ
. This study demonstrates different requirements by the cathodes in the non-aqueous and aqueous systems and offers a new idea for improving the performance and stability of the electrodes for aqueous cells.
Accurate design of high‐performance 3D surface‐enhanced Raman scattering (SERS) probes is the desired target, which is possibly implemented with a prerequisite of quantifying formidable multiple ...coupling effects involved. Herein, by combining theory and experiments on 3D periodic Au/SiO2 nanogrid models, a generalized methodology of accurately designing high performance 3D SERS probes is developed. Structural symmetry, dimensions, Au roughness, and polarization are successfully correlated quantitatively to intrinsic localized electromagnetic field (EMF) enhancements by calculating surface plasmon polariton (SPP), localized surface plasmon resonance (LSPR), optical standing wave effects, and their couplings theoretically, which is experimentally verified. The hexagonal SERS probes optimized by this methodology realize over two orders of magnitudes (405 times) improvement of detection limit for Rhodamine 6G model molecules (2.17 × 10−11 m) compared to the unoptimized probes with the same number density of hot spots, an enhancement factor of 3.4 × 108, a uniformity of 5.52%, and are successfully applied to the detection of 5 × 10−11 m Hg ions in water. This unambiguously results from the Au roughness‐independent extra 144% contribution of LSPR effects excited by SPP interference waves as secondary sources, which is very unusual to be beyond the conventional recognition.
A generalized methodology of designing 3D surface‐enhanced Raman scattering (SERS) probes with superior detection limit and uniformity is developed by maximizing intrinsic electromagnetic field enhancements from multiple coupling effects of localized surface plasmon resonance, surface plasmon polariton, and optical standing wave. The designed 3D periodic Au/SiO2 SERS probes experimentally realize over 102 improvement of detection limit with superior uniformity.
► The thermoelectric (TE) properties of the doped Mg2Si were theoretically studied. ► The electronic transport properties were calculated with the BoltzTraP code. ► The lattice thermal conductivity ...was estimated with an empirical model. ► The calculated TE properties agree qualitatively with the experiments.
Mg2Si has been regarded as a potential candidate for thermoelectric applications in middle-temperature range (500–900K). In order to better understand the temperature, doping level and composition dependent thermoelectric properties, we performed simulations that are based on the semi-classical electronic transport theory and the empirical lattice thermal conductivity model. The temperature and doping level dependence of the calculated Seebeck coefficients and electrical conductivity agree qualitatively with the previous experiments. By considering the influence of the chemical composition on the lattice thermal conductivity, we further estimated the thermoelectric figure-of-merit (ZT) for the Sb-doped Mg2Si samples. The results reproduced the temperature variation trends of the ZT values in the literature. The current work represents an attempt to combine the first-principles tools and the empirical models to evaluate the TE properties of the Mg2Si materials. It may shed some light on developing Mg2Si-based thermoelectric devices in the future.
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