Search

Thermoelectric generators (TEGs) demonstrate great potential for flexible and wearable electronics due to the direct electrical energy harvested from waste heat. Good wearability requires high mech...

Oxygen deficiencies are well recognized to have a detrimental effect on the performance of spinel LiMn2O4-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 LiMn2O4-δ by calcination of oxygen deficiency-free LiMn2O4 at 850 °C for 2 h followed by quenching in air. LiMn2O4-δ primary particles show the octahedral shape, the sizes of about 400 nm, and the larger lattice constant of 8.240 A, in contrast with the irregular shapes, the sizes of about 100 nm, and the lattice constant of 8.231 A. In the non-aqueous system, the performances for LiMn2O4-δ are inferior compared to LiMn2O4, as reported previously. However, both LiMn2O4-δ||polyimide and LiMn2O4||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 H2O decomposition observed at about 1.85 V for LiMn2O4 leads to much poorer performance which is absent for LiMn2O4-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.

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts have been of interest to researchers. Despite remarkable progress in moving TE fibers toward room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, interfacial-engineering-enhanced TE properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi

Achievement of carbon materials with particular structures, dimensions, and sizes derived from metal organic frameworks (MOFs) with particular morphologies is very crucial for purpose-oriented appl...

Commercialized lithium cobalt oxide (LCO) only shows a relatively low capacity of ≈175 mAh g

Low-cost Mn- and Li-rich layered oxides suffer from rapid voltage decay, which can be improved by increasing the nickel content to derive high nickel Li-rich layered oxides (HNLO) but is normally accompanied by reduced capacity and inferior cycling stability. Herein, Na or K ions are successfully doped into the lattice of high nickel Li-rich Li

Discarded polystyrene foams as white wastes, at least two million tons in demand annually in China, are threatening environment and health because of their formidable degradation, which increase in...

Bismuth telluride (Bi2Te3) has attracted much attention in the field of thermoelectrics since it is one kind of commercial room-temperature thermoelectric material. Herein three kinds of Bi2Te3 thermoelectric fibers with internal tensile stress are fabricated utilizing an optical fiber template method. The effects of internal stress on the microstructure and the electrical transportation of Bi2Te3 thermoelectric fibers are investigated. The Bi2Te3 cores in the fibers are highly crystalline and possess a tensile nanosheet structure with preferential orientation as evidenced by X-ray diffraction and Raman studies. Tensile stress can enhance electrical properties of the fibers. And a paper cup generator covered with 20 pieces of optimized fibers provides a μW-level output power. It is inferred that tensile stress tuning can be an effective tool for the material optimization of thermoelectric performance.

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.

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO2, different binary metal oxide-based sensors were developed to achieve superior performance at elevated temperatures instead of RT. Herein, we report on CuO@CuO and Cu3Mo2O9@CuO sensors with CuO and Cu3Mo2O9 micro/nanorods vertically aligned on the CuO layers, which were directly fabricated using a facile, low-cost, and catalyst-free chemical vapor deposition (CVD) technique. Their sensing performance tests revealed that the Cu3Mo2O9@CuO p-p heterojunction sensors exhibited a high response of 160% to 5 ppm NO2, an excellent sensitivity of 50% ppm-1, a low LOD of 2.30 ppb, a short response time of 49 s, and a rapid recovery of 241 s at RT, obviously better than those for CuO@CuO sensors. The superior performance of Cu3Mo2O9@CuO sensors could be attributed to the Schottky heterojunction formed between p-Cu3Mo2O9 micro/nanorods and p-CuO films, the catalytic effect, and the anisotropic nature of Cu3Mo2O9 micro/nanorods. This study not only provides a simple, low-cost, and batchable fabrication method of homo/heterojunction sensors with micro/nanorods vertically aligned on films but also opens an avenue for sensor design by tuning the Schottky barrier height to enhance RT performance.

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.

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO2/graphene hybrid field effect transistor (FET) sensors (TiO2/GFET) with varied hybrid areas are presented. Superior sensing and recovery performances for NH3 are achieved through sensing mode switch via gate biasing. 16.40% response and full recovery for 25 ppm NH3 are achieved for TiO2/GFET sensors with 100% titanium dioxide coverage (D100) at RT (27 °C) with 15-20% humidity upon switching sensing mode from p- to n via gate biasing. Full recovery is attributed to the Coulomb interaction between charged polar donor molecules and positively polarized surface which is enhanced by the switch from p- to n-mode. The humidity can enhance response up to -35.48% for 25 ppm NH3 with full recovery in n-mode for D100. D100 shows superior selectivity towards NH3 against both electron-acceptor NO2 and several other electron-donor analytes. The sensing behaviors for NH3 are well elucidated using energy band diagrams based on the experimental results. This study proposes a novel idea for performance improvement of FET based sensors with p- and n-type hybrid sensing materials through p (n)- to n (p)-mode switch assisted by gate biasing by incorporating suitable electron (hole) rich materials to compensate holes (electrons) in p (n)-type materials for electron donor (acceptor) gas detection.

Effective detection of NO2 and NH3 gases at room temperature (RT) is critical for environmental monitoring and protection. Here, graphene-based gas sensors (Cu/Gr device) of single layer graphene decorated by 6, 8 and 10 nm thick Cu layers with graphene instead of conventional metal as interdigital electrodes are designed and fabricated. The RT performance for both NO2 and NH3 detection can be greatly enhanced by UV light illumination which is closely related to the thickness of Cu layers in which the device with 8 nm thickness (8 nm Cu/Gr device) exhibits the best performances. Analysis of XPS reveals that Cu is partly oxidized to Cu+ and Cu2+ for 6 nm with extra Cuδ+ (1 < δ < 2) for 8 and 10 nm. The contents and distributions of copper oxides and copper in Cu layers influence the catalytic effects and the heterojunction barrier and thus the performances. The RT responses of −30.9% and −8.1% for 5 and 0.3 ppm NO2, and of +29.1% and +5.9% for 105 and 10 ppm NH3 are achieved for the 8 nm Cu/Gr device, respectively. The limits of detection (LODs) for NO2 and NH3 are 12 ppb and 17 ppb, respectively. The sensing mechanisms are discussed in terms of density functional theory (DFT) calculations and energy band diagrams. The study demonstrates an effective solution of improving the device performance by modifying the device configuration and incorporating combined oxides naturally oxidized, which provides the novel design alternatives for high performance sensors.

High-performance thermoelectric (TE) materials with great flexibility and stability are urgently needed to efficiently convert heat energy into electrical power. Recently, intrinsically crystalline, mechanically stable, and flexible inorganic TE fibers that show TE properties comparable to their bulk counterparts are of interest to researchers. Despite remarkable progress moving TE fibers towards room-temperature TE conversion, the figure-of-merit value (ZT) and bending stability still need enhancement. Herein, we report interfacial engineering enhanced thermoelectric properties of micro-nano polycrystalline TE fibers fabricated by thermally drawing Bi2Te3-based bulks in a glass-fiber template. The interfacial engineering effect comes from generating stress-induced oriented nanocrystals to increase electrical conductivity and producing strain-distorted interfaces to decrease thermal conductivity. The resulting fibers achieve a 40% higher ZT (~1.4 at 300 K) than their bulk counterparts and show a reversible bending radius of 50 µm, approaching the theoretical elastic limit. This fabrication strategy works for a wide range of inorganic TE materials and benefits the development of fiber-based micro-TE devices.

Li- and Mn-rich layered oxides can deliver high reversible capacity but suffer from severe voltage decay, which seriously impedes their commercial applications. However, high-nickel Li-rich layered oxides could normally present stable discharge voltage but tend to deliver low reversible capacity. In this work, high-nickel Li-rich layered oxides are doped by Mo via a facile sol-gel route to realize both high reversible capacity and minor voltage decay simultaneously. The superior performance could be ascribed to the reduced size of primary particles, the enhanced stability of lattice oxygen and more Mn4+/3+ redox couples effectively activated during the electrochemical reactions which are realized via Mo doping. The present study offers a new strategy to achieve high-performance high-nickel Li-rich layered oxides with both the stable discharge potential and high reversible capacity by modifying their morphologies, structures and chemistries via the introduction of proper alien elements which are believed to be the potential cathode candidates for next generation lithium-ion batteries.

It has been well recognized that Li2CO3 is inevitably formed at the surface of nickel rich layered compounds (NRLC) upon storage in air which is usually considered to be detrimental to the performance. Actually, its formation may have been triggered during synthesis of NRLC. However, little is known of its formation during synthesis of NRLC in air and its interaction behaviors with electrolyte during electrochemical process. Herein, we successfully tailor Li2CO3 surface phase simply by controlling calcination time during synthesis of structurally well ordered LiNi0.9Mn0.1O2 particles with great similarity in structure, morphology, size and crystallinity in air using a facile sol-gel method. The thickness of Li2CO3 layer is for the first time observed to decrease with increased calcination time, accompanied by the reduced Ni2+ at surface. More oxygen vacancies caused by more Ni2+ owing to the difficulty of oxidizing Ni2+ to Ni3+ at the surface are proposed here to be responsible for the formation of more Li2CO3 for shorter calcination times. Li2CO3 surface phase is evidenced to favor not only suppressing the H2/H3 phase transition but alleviating the interaction of LiNi0.9Mn0.1O2 with electrolyte because of the coating effect, which therefore improves the cycling stability of LiNi0.9Mn0.1O2 at low rates. Therefore, this study not only provides a new insight into the surface changes of LiNi0.9Mn0.1O2 with calcination time at high temperature during synthesis in air, but opens up a new avenue to tailoring Li2CO3 surface phase as desired by controlling the oxidization extent of Ni2+ to Ni3+ to modulate oxygen vacancies at surface through employing different oxidizing atmospheres or calcination times for performance improvement or exploration of novel preparation approaches of high performance NRLC.

The switch in the sensing mode for better identification of donor/acceptor gases with simultaneous enhancement of the sensing performance at a fixed working temperature particularly room temperature (RT) is quite challenging for gas sensors. Herein, TiO

High sensitivity, low limit of detection (LOD), and short response and recovery times at room temperature (RT) are critical for gas sensors. For NO

A numerical modeling study based on 3D finite element method (FEM) simulation and 1D analytical solutions has been carried out to evaluate the capabilities of two ac methods for measuring in-plane thermal conductivity of thin film deposited on the back of a suspended SiNx membrane setup. Two parallel metal strips are present on the top of the dielectric membrane. One strip (S1) serves as both heater and thermometer, while another one (S2) acts as thermometer only. For a modified phase shift (MPS) method, it is crucial to extract the in-plane thermal diffusivity from the phase shift of the temperature oscillation on S2. It was found that the frequency window for carrying out the data fitting became narrower as the in-plane thermal diffusivity of the composite membrane (${\alpha_{\parallel ,C}}$) increased, primarily due to the failure of the semi-infinite width assumption in the low frequency region. To ensure the validity of the method, the upper limit of ${\alpha_{\parallel ,C}}$ should not exceed ~1.8$ \times $10-5 m2 s-1 for the specific membrane dimension under consideration (1$\times $1 mm2). On the other hand, inspired by a modified Angstrom method proposed by Zhu recently, we suggest a new data reduction methodology which takes advantage of the phase shift on both S1 and S2 as well as the amplitude on S1. Based on the simulation results, it is expected that the non-ideality associated with the three observables may be at least partially cancelled out.Therefore, the frequency window selection for carrying out the data fitting is not sensitive to the magnitude of ${\alpha_{\parallel ,C}}$. For typical specimen films whose in-plane thermal conductivity ranges from 0.84 W m-1 K-1 to 50 W m-1 K-1, the method proposed here yields a theoretical measurement uncertainty of less than 5%., Comment: 34 pages, 9 figures

The silane coupling agent 3-aminopropyltriethoxysilane (KH-550) was used to modify the surface of two kinds of high-performance polyimide (PI) fibres (i.e., PI-1 and PI-2). The surface chem...

Very recently, amino-substituted perylene diimides (PDINE) and naphthalene diimides (NDINE) have been reported as good n-type thermoelectric (TE) materials; rational design of their derivatives is strongly desired to further enhance their TE performance. In this study, based on the molecular structure of PDINE and NDINE, a series of acridones with different terminal tertiary amine groups (ADTA) at the C2 and/or C7 positions of the acridone ring was designed and synthesised as potential n-type TE materials. Then, single-walled carbon nanotubes (SWCNTs) were combined with the acridones to form flexible SWCNT/ADTA composite films. The composites exhibited excellent n-type TE performance. Furthermore, the terminal tertiary amine and the number of side chains greatly affected the TE properties of the composites. The composite containing an acridone with two terminal diethyl amine groups displayed the highest power factor of 289.4 ± 2.8 μW m−1 K−2 at 430 K, which is perhaps one of the highest values reported to date for a composite containing n-type small organic molecules and SWCNTs. In addition, the composite with a functionalised piperidine acridone displayed p-type TE behaviour with a high power factor of 211.6 ± 9.9 μW m−1 K−2 at room temperature. Our results demonstrate that SWCNT/acridone composites with appropriate substituents show promise as TE materials, which opens a new avenue for TE material design.

Exploiting the thermal insulation properties of glass fiber and excellent conductivity of conducting polymer, a novel one-dimensional (1D) composite thermoelectric material, based on poly(3,4-ethylenedioxythiophene): p-toluenesulfonic acid (PEDOT: p-TSA)/glass fiber, is prepared by coating the PEDOT: p-TSA on the surface of glass fiber with in situ polymerization method. We hope the materials can bring out the performance of the “electron conductor, photon glass”. During the polymerization process, the effects of oxidant concentration and dopant mass fraction on thermoelectric properties of the materials are investigated. The group type of the polymer chain and the morphology of the samples were characterized by Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM), respectively. The maximal Seebeck coefficient (S) and electric conductivity (σ) of the pristine sample are 32 μVK-1 and 169 Sm-1, respectively. After further post-processing with methanol, the thermoelectric properties of materials were improved, and the maximum value of S and σ increased greatly to 48.5 μVK-1 and 3184 Sm-1, respectively. The maximal power factor (PF) of materials also increased from 0.12 μWm-1 K-2 to 6.74 μWm-1 K-2. Moreover, we have proposed a preliminary explanation on the carrier transport mechanism.

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.

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 = P max m Δ T N , where the maximum output power (P max) 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.