High Temperature Energy Harvesting Research Articles

Flexible stretchable tribo-negative films with exceptional output performance for high-temperature energy harvesting and self-powered sensor

High temperature is a significant cause of failure of electromechanical products, achieving effective collection of triboelectric energy at high-temperatures is a major research emphasis. Improving the electrical outputs from triboelectric nanogenerator (TENG) in extreme environments is crucial for its large-scale application and remains challenging. Further considering the major potential application for TENG is wearable electronics, a series of SEBS/fatty acid (SEBS/FA) skin-like flexible films were fabricated, which exhibit adjustable surface triboelectricity and enhanced triboelectric outputs at high-temperatures. The SEBS/FA based TENGs possess remarkable durability of over 10,000 contact-separation cycles, and exhibit exceptional electrical outputs in the heat. Thereinto, the output efficiency of SEBS-OA (octanoic acid) is up to 302.32 % at 110 °C and still above 100 % at 150 °C. The SEBS/FA based TENGs can efficiently harvest the mechanical energy in high-temperature environments to power commercial capacitors and LEDs. Notably, the SEBS/FA films still show enhanced electrical outputs even under extreme conditions with working ambient temperatures up to 90 °C and significant deformation (λ ≤ 4). The excellent electromechanical performances enable SEBS/FA based TENGs to be served as flexible energy collector and self-powered touch sensor for motion capture. The real-time tactile trajectory can be accurately mapped by a 5 × 5 sensing array. The SEBS/FA films exhibit great potential in energy harvesting and active real-time tactile sensing system in extreme environments.

A large-area bionic skin for high-temperature energy harvesting applications

A large-area bionic skin for high-temperature energy harvesting applications

Augmented thermoelectric performance of LiCaX (X = As, Sb) Half Heusler compounds via carrier concentration optimization

The present study is focussed on the detailed physical insight into the structural, thermal, and dynamical properties of 8-valence electron Half Heusler (HH) compounds LiCaX (X = As, Sb) using Density functional theory. The thermal and dynamic stabilities of the compounds are assessed via ab-initio molecular dynamic simulations and phonon dispersion calculations, respectively. The Tran-Blaha modified Becke Johnson potential is used to accurately predict the band gap of investigated compounds. It is found that they are indirect band gap semiconductors with band gaps of 2.52 eV (LiCaAs) and 2.09 eV (LiCaSb). The transport parameters are obtained for p-type and n-type doping at temperatures ranging from 300 K to 800 K by solving the Boltzmann Transport equation. The deformation potential theory is employed to calculate the temperature dependent relaxation time for both compounds. The results of the various thermoelectric parameters obtained using actual values of time-dependent relaxation time are compared with that calculated under constant relaxation time approximation. The maximum power factor is 10.95 × 1011 (4.99 × 1011) Wm−1K−2s−1 for p-type (n-type) LiCaAs and 12.53 × 1011 (5.30 × 1011) Wm−1K−2s−1 for p-type (n-type) LiCaSb at optimized carrier concentration. The obtained low lattice thermal conductivities for LiCaSb (0.66 Wm−1K−1) and LiCaAs (0.88 Wm−1K−1) are explicated it in terms of different phonon modes. The Figure of Merit at 800 K for p-type (n-type) LiCaAs is as high as 0.90 (0.73) and 0.93 (0.84) for LiCaSb at optimum carrier concentration ∼1020 cm−3 (∼1019 cm−3), which has been experimentally realized in other 8-valence electron Li-based HH compounds. The good thermoelectric performance of p-type LiCaX in comparison to n-type suggests that p-type LiCaX alloys are viable candidates for high temperature energy harvesting applications.

Synchronously enhanced thermoelectric and mechanical properties of Ti doped NbFeSb based half-heusler alloys by carrier regulation and phonon engineering

NbFeSb based half-heusler thermoelectric materials have great potential in high-temperature energy harvesting. However, their conversion efficiency is limited by the low figure of merit zT, which is attributed to poor electronic performance and high thermal conductivity. Here, it is demonstrated that enhanced power factor of 46 μW cm−1 K−2 and zT value of 0.9 at 973 K is achieved in spark plasma sintered Nb0.8Ti0.2FeSb. It is depicted that a tremendous increase in the hole concentration owing to Ti substitution, results in a significant promotion of electrical performances. In addition, numerous phonon scattering centers, such as point-defects, nano precipitates as well as electro-acoustic coupling, collectively suppress the lattice thermal conductivity from 7.4 W m−1 K−1 to 3.3 W m−1 K−1 at 973 K. Furthermore, NbFeSb based alloys exhibit excellent mechanical property and the Vickers hardness reaches 10.8 GPa, which would be beneficial for TE devices fabrication.

Large piezoelectricity in BiScO3-PbTiO3 based perovskite ceramics for high-temperature energy harvesting

Advanced high-temperature piezoceramic energy harvesters (HT-PEHs) highly rely on perovskite ceramics with large high-temperature piezoelectricity. However, it remains a great challenge to achieve high piezoelectric coefficient (d33) at elevated temperatures, which severely limits the development of piezoelectric materials in cutting-edge energy harvesting applications. Here, yBiScO3-xPbTiO3-0.05Pb(Zn1/3Nb2/3)O3 (yBS-xPT-PZN) ternary perovskite piezoceramics are prepared, in which the morphotropic phase boundary (MPB) composition (x/y = 0.60/0.35) exhibits a large d33 of 655 pC/N at 300 °C, outperforming many reported other perovskite piezoceramics. The excellent high-temperature piezoelectricity should benefit from the lattice softening effect and the stable ferroelectric domain state associated with the high tetragonal phase content. In addition, the HT-PEH assembled from the MPB sample exhibits good power generation performance (e.g., a giant power density of 418 μW/cm3) at 300 °C, and can charge a 10 μF commercial capacitor to 7 V within 40 s. Such a large piezoelectric coefficient and power density of yBS-xPT-PZN system at a high temperature of 300 °C is a promising candidate for fabricating high-performance HT-PEHs to meet the urgent requirements of advanced high-temperature energy harvesting applications.

Broadband Metamaterial Solar Absorbers Based on the Earth First-rate Temperature-Insensitivity Metals for High Temperature Energy Harvesting

Artificially engineered solar absorbers, known as metamaterial solar absorbers (MSA), are yielding new opportunities for designing new photons management systems. Furthermore, the noble metals are indispensable in creating MSA owing to their plasmonic resonance in a desired spectral region. Nevertheless, in high temperature applications, the noble metals suffer from low melting points that make their uses largely impractical. In this work, the solution of using four of the Earth first-rate temperature-insensitivity metals in a proposed MSA is investigated. The proposed MSA structure is composed of high melting point metals (HMPM), deposited on a magnesium fluoride (MgF\(_2\)) dielectric spacer and a tungsten continuous plate. Meanwhile, owing to the dependence of MSA properties on structural parameters rather than band structure or chemistry, a geometrical optimization of the proposed absorbers is reported. Furthermore, the proposed MSA performance is investigated by computing the absorption spectrums. Results show relatively long bandwidths in the visible and near-infrared regimes. Besides, an underlying mechanism of the absorption enhancement with the corresponding electromagnetic field distributions is elucidated in detail. The calculated results indicate that the proposed MSA present wide bandwidths owing to the excitation of resonance modes of surface plasmons, dipolar interactions and cavity modes. Equally important, absorption measurements under wide polarization angles show polarization-insensitive high absorption at higher wavelengths, which is among the most important factors for an ideal solar absorber. The conclusion of this investigation is undoubtedly important, specifically that the proposed HMPM-based MSA would be the best choice for energy harvesting in high temperature applications.

Lead titanate nanowires/polyamide-imide piezoelectric nanocomposites for high-temperature energy harvesting

With an increasing demand for self-powered microelectronics to be used in scientific tasks and exploration missions in extreme environments, the implementation of piezoelectric energy harvesting at high temperature is an important research focus for renewable energy sources. Piezoelectric composites made from piezoelectric ceramic fillers and polymer matrices combine high electromechanical coupling with flexibility, resulting in a versatile candidate for energy harvesting. In this research, a nanocomposite formed by lead titanate nanowires (PbTiO3 NWs) and a polyamide-imide (PAI) matrix is developed and shown to have an excellent piezoelectric response at high temperatures. By in situ measurements of the piezoelectric g31 and d31 coefficients of the nanocomposite films with different PbTiO3 NW weight fractions in the temperature range 25–250 °C, the dependence of temperature and filler concentration on the piezoelectric properties are fully characterized. In addition, the effect of NW alignment on piezoelectric properties through direct ink writing is also studied. Finally, a bending-mode energy harvester made from this nanocomposite is demonstrated to generate a maximum power density of 33 μW·m−2 at resonance and a power density of 20 μW·m−2 under low-frequency random excitation at 200 °C, while keeping a long operating life of at least 100 h. In conclusion, this work provides a new solution for high-temperature energy harvesting from low-frequency random vibrations using PbTiO3/PAI nanocomposites.

Enhanced transduction coefficient and thermal stability of 0.75BiFeO3-0.25BaTiO3 ceramics for high temperature piezoelectric energy harvesters applications

Owing to the coexistence of high depolarization temperature of 500 °C and good piezoelectric properties, 0.75BiFeO3-0.25BaTiO3-0.5mol%MnO2 (BFBTMn) ceramics show potential energy harvesting applications at elevated temperature. Chemical modifications are usually difficult to improve transduction coefficient (d33×g33) due to the opposite directions of d33 and g33. Herein, the BFBTMn ceramic powders with different average grain sizes of 500 (S1), 700 (S2) and 800 (S3) nm were mixed together for ceramics preparation. This method promotes the grain size, relative density and rhombohedral phase volume fraction of BFBTMn ceramics, leading to the much improved piezoelectric transduction coefficient and its thermal stability. The transduction coefficient of ceramics with optimized weight ratio (1S1:2S2:1S3) reaches up to 4644 × 10−15 m2/N, about 51% higher than those without mixed powder and at least 60% higher than those reported in the literatures, while its degradation from room temperature to 500 °C is about 15%, much smaller than that (30%) of ceramics without mixed powders. These investigations pave a new way to tailor the transduction coefficient and its thermal stability of BF-BT piezoelectric ceramics for high temperature energy harvesting devices.

Excellent high-temperature piezoelectric energy harvesting properties in flexible polyimide/3D PbTiO3 flower composites

Piezoelectric nanogenerators (PENGs) have been paid great attention in powering electronics via harvesting mechanical energy. Presently, increasing lights are shed onto flexible PENGs capable of working at harsh temperatures. In this research, we report a synthesis of 3D hierarchical PbTiO3 flower-like structure (PTFs) and polyimide (PI)/PTFs composites from which PENGs with excellent high-temperature energy harvesting performances are fabricated. PTFs exhibit a pure phase and a 3D architecture obtained by the hydrothermal method. The PI/PTFs composite PENGs exhibit good electricity-generation performances of Voc ~ 140 V, Isc ~ 103 μA and P ~ 2128 μW. Moreover, high degree of electric power can be continuously generated by the PENG at a wide range of temperature from room-temperature to 300 °C. Excellent durability up to 5000 cycles can be also obtained for the PENG within the temperature range. It has been demonstrated that a PENG in this study lights fifty light-emitting diodes and the resulting electricity is successfully stored in a capacitor. In addition, a real-time high-temperature application is presented where harvesting electricity via the vibration energy of the running automobile engine occurs. The outstanding piezoelectric performance of PENG in this study is attributed to the thermal stability of PI and PT materials, and unique 3D architectures of PTFs in the composites. This work reveals a PI/PTFs composite based PENG exhibiting excellent energy harvesting properties at high-temperatures and the potential applications as microenergy harvesters.

Giant high-temperature piezoelectricity in perovskite oxides for vibration energy harvesting

Based on the lattice distortion modulation strategy, a record-high in situ quasi-static d33 at 400 °C is achieved in a 0.355BiScO3-0.635PbTiO3-0.01Bi(Zn0.5Hf0.5)O3 perovskite ceramic used in high-temperature energy harvesting.

Thermoelectric Properties of Iron Disilicide and Manganese Silicide: Synthesis and Characterization

Among the thermoelectric materials, silicides are the group of thermoelectric materials which are eco-friendly (Han et al. in Aust Inst Innov Mater (Chin Sci Bull) 59: 2073, 2014) and can be considered as the promising high-temperature energy harvesting materials. The exclusivity about the synthesis route used is that it is economical, scalable and less time-consuming (20-h synthesis period), and minimum metallic content in the synthesized samples and same milling setup was used to synthesize two different high-temperature silicides, that is, iron disilicide and manganese silicide. The Seebeck coefficient was found to increase gradually with the increase in temperature and was found to be more for MnSi1.73 (156 μV/K at 1150 K) than β-FeSi2 (135 μV/K in the temperature range of about 1000–1050 K). The MnSi1.73 (0.37) was found to have higher ZT value than β-FeSi2 (0.23).

A wide temperature insensitive piezoceramics for high‐temperature energy harvesting

AbstractOne of the key challenges in the development of high‐temperature energy harvesting (HTEH) technology is to clarify the relationship between temperature‐dependent material parameters and device power generation capabilities. However, at present, the research on temperature stability of piezoceramics mainly relies on thermal annealing technology, which cannot follow the actual temperature dependence of the piezoelectricity, and it is even more difficult to predict the temperature stability of HTEH. To shed light on this field, here, (1−x)BiScO3–xPbTiO3 system was chosen for building HTEH material, and the temperature‐dependent electrical parameters, such as d33, εr, and g33, have been measured by multiple in situ techniques. It was found that the synergistic effect of d33 and εr with temperature helps to obtain a stable g33 value in a wide temperature range. Moreover, in the mode of the cantilever‐type energy harvester, a stable output voltage was obtained at x = 0.64 harvester with <20% change over a broad temperature range of 100‐250°C, and it was verified that the temperature stability of g33 is crucial to the operation stability of HTEH devices.

Refractory Brewster metasurfaces control the frequency and angular spectrum of light absorption

Ways to achieve highly efficient electromagnetic absorption over a broad bandwidth and broad angular spectrum have been discussed extensively in the past decades for various applications, such as low reflection devices and energy harvesting. To satisfy the efficiency requirements, metamaterial approaches have been explored in recent years. In this context, most studies have suggested the use of frequency selective surfaces or arrays of plasmonic resonators, which limit bandwidth and angular spectrum of performance. Here, we explore the application of refractory Brewster metasurfaces for photovoltaic applications. By matching the surface impedance of metasurfaces and free space at the Brewster angle, we show that metasurfaces can lead to efficient light absorption, and their response can be controlled accurately both in the angular and in the frequency spectrum to match the requirements of energy harvesting systems and facilitate large efficiency, high-temperature energy harvesting.

Feasibility study of thermal energy harvesting using lead free pyroelectrics

Energy harvesting has significant potential for applications in energizing wireless sensors and charging energy storage devices. To date, one of the most widely investigated materials for mechanical and thermal energy harvesting is lead zirconate titanate (PZT). However, lead has detrimental effects on the environment and on health. Hence, alternative materials are required for this purpose. In this paper, a lead free material, lithium niobate (LNB) is investigated as a potential material for pyroelectric energy harvesting. Although its theoretical pyroelectric properties are lower compared to PZT, it has better properties than other lead free alternatives such as ZnO. In addition, LNB has a high Curie temperature of about 1142 °C, which makes it applicable for high temperature energy harvesting, where other pyroelectric ceramics are not suitable. Herein, an energy harvesting and storage system composed of a single crystal LNB and a porous carbon-based super-capacitor was investigated. It is found that with controlled heating and cooling, a single wafer of LNB (75 mm diameter and 0.5 mm thickness) could generate 437.72 nW cm–3 of power and it could be used to charge a super-capacitor with a charging rate of 2.63 mV (h cm3)–1.

High quality thin films of thermoelectric misfit cobalt oxides prepared by a chemical solution method.

Misfit cobaltates ([Bi/Ba/Sr/Ca/CoO]nRS[CoO2]q) constitute the most promising family of thermoelectric oxides for high temperature energy harvesting. However, their complex structure and chemical composition makes extremely challenging their deposition by high-vacuum physical techniques. Therefore, many of them have not been prepared as thin films until now. Here we report the synthesis of high-quality epitaxial thin films of the most representative members of this family of compounds by a water-based chemical solution deposition method. The films show an exceptional crystalline quality, with an electrical conductivity and thermopower comparable to single crystals. These properties are linked to the epitaxial matching of the rock-salt layers of the structure to the substrate, producing clean interfaces free of amorphous phases. This is an important step forward for the integration of these materials with complementary n-type thermoelectric oxides in multilayer nanostructures.

(Invited) Computation-Driven Materials Search for Thermoelectric Applications

Solid-state thermoelectric (TE) devices have the ability to directly convert heat into electricity for power generation. Despite its many energy-harvesting applications, the potential impact of TE technology is largely hindered by the relatively low performance of commercial materials. In physics, the effectiveness of TE materials is evaluated by their TE figure of merit (ZT), defined as ZT = S 2 σT/k, where S, σ, k, and T represent Seebeck coefficient, electrical conductivity, thermal conductivity, and absolute temperature, respectively. Here k can be further split into the lattice contribution kL and electronic contribution kE . Within the same material, challenge exists in obtaining a low k but a high power factor S 2 σ. As the result, ZTs of commercial materials are still around unity after decades of research though ZT>2 is preferred for TE to compete with other technologies. Along this line, nanostructured bulk materials, which are synthesized by hot pressing nanopowder into a bulk material, have been widely studied as an effective approach to improve ZTs of existing or novel materials [1]. By introducing nanostructured interfaces within a bulk material, the interdependent electron and phonon transport can be decoupled to dramatically reduce kL but still maintain S 2 σ, resulting in enhanced ZT. Unrestricted to conventional materials, this approach may also lead to high ZTs in unconventional TE materialswith both a high S 2 σ and a high kL , such as bulk Si [2,3]. This will reach beyond conventional materials that heavily depend on toxic, rare, and expensive elements, e.g. Te. Based on the nanostructuring approach, broad material search is in urgent need for novel TE materials using nontoxic, cheap, and abundant elements. For computation-driven TE material search, challenge generally exists in accurately predicting the energy-dependent electron and phonon mean free paths (MFPs) for TE property predictions. For phonon transport, there exist first-principles-based studies for standard materials such as Si and Ge. However, such calculations are intrinsically very time-consuming and are limited to relatively simple material structures. On the other hand, first-principles electrical property predictions are also restricted to well-studied materials and are thus unsuitable for high-throughput material search, in which thousands of complicated materials will be screened based on the computed ZTs. As the result, highthroughput TE material search is mostly based on S 2 σ/τ or ZTs further estimated with guessed kL /τ values [4-6], in which τ is the averaged relaxation time of all charge carriers. For materials screening, experimental inputs of σ and kL are often required and the guidance from computations becomes very limited. For nanograined bulk materials synthesized by hot press, however, the need of computing electron and phonon MFPs can be eliminated when these MFPs are largely restricted by the grain size. In such materials, the optimum grain size should be larger than electron MFPs but shorter than phonon MFPs to reduce kL without deteriorating σ. The maximum ZT is anticipated when the grain size is reduced to the majority electron MFPs, called the small-grain-size (SGS) limit for nanograined bulk materials [7]. This simple treatment has been used to compare the power factor of new TE materials [8] but no ZTs are computed without phonon calculations. In this work, we propose a ZT formulation of general materials under the SGS limit, which is solely based on phonon dispersions and electronic band structures predicted by first-principles calculations. The materials search is demonstrated with representative oxides that can be potentially used for high-temperature energy harvesting.

Nanoscale flexoelectric energy harvesting

One of the most tantalizing applications of piezoelectricity is to harvest energy from ambient mechanical vibrations for powering micro and nano devices. However, piezoelectricity is restricted only to certain materials and is severely compromised at high temperatures. In this article, we examine in detail, the possibility of using the phenomenon of flexoelectricity for energy harvesting. The flexoelectric effect is universally present in all dielectrics and exhibits a strong scaling with size. Using a simple beam-based paradigmatical design, we theoretically and computationally examine flexoelectric energy harvesting under harmonic mechanical excitation. We find that the output power density and conversion efficiency increase significantly when the beam thickness reduces from micro to nanoscale and flexoelectricity-based energy harvesting can be a viable alternative to piezoelectrics. Specifically, the conversion efficiency in flexoelectric transduction at sub-micron thickness levels is observed to increase by two orders of magnitude as the thickness is reduced by an order of magnitude. The flexoelectric energy harvester works even for a single layer beam with a symmetric cross section which is not possible in piezoelectric energy harvesting. Our results also pave the way for exploration of high temperature energy harvesting since unlike piezoelectricity, flexoelectricity persists well beyond the Curie temperatures of the high electromechanical coupling ferroelectrics that are often used.

Temperature dependence of flexoelectricity in BaTiO3 and SrTiO3 perovskite nanostructures

Abstract Piezoelectricity is a property of non-centrosymmetric crystals. In most typically used ferroelectrics, this property is lost as the temperature is increased beyond the Curie point thus strongly reducing the availability of efficient materials that can be used for high temperature energy harvesting. Flexoelectricity, as can be shown from simple symmetry arguments, is a universal and linear electromechanical coupling that dictates the development of polarization upon application of inhomogeneous strains. The implications of this phenomenon become amplified at the nanoscale. In this communication, we develop a molecular dynamics approach predicated on a specially tailored interatomic force-field to extract the temperature dependence of flexoelectricity. Surprisingly, we find that it, at least for Barium Titanate and Strontium Titanate nano structures, increases with temperature. Apart from cataloging this interesting observation for the future use in high temperature energy harvesting, we also examine the physical mechanisms that lead to the observed temperature dependence.

Thermoelectric Energy Conversion and Ceramic Thermoelectrics

Oxide thermoelectrics are relatively new materials that are workable at temperatures in the range of 400K≤T≤1200K. There are several types of thermoelectric oxide, namely, cobalt oxides (p-type semi-conductors), manganese oxides (n-type) and zinc oxides (n-type semi-conductors) for high temperature energy harvesting. The Seebeck coefficient of 3d metal oxide thermoelectrics is relatively high due to either high density of states at Fermi surfaces or spin entropy flow associated with the carrier flow. The spin entropy part dominates the Seebeck coefficient of 3d-metal oxides at temperatures above 300K. Introduction of impurity particles or quantum-well structures to enhance thermionic emission and energy filtering effects for the oxide semiconductors may lead to a significant improvement of thermoelectric performance.

Silicon Carbide Based Energy Harvesting Module for Hostile Environments

This paper demonstrates the rst high temperature silicon carbide based energy harvesting module suitable for use in hostile environments. The system comprises a of SiC pin photovoltaic cell, HfO2 based capacitive storage bank and Schottky blocking diode. The system demonstrates the ability to harvest energy from a UV rich environment and store this energy on a HfO2 metal - insulator - metal (MIM) capacitor bank. The system unies work thathas focussed on developing high temperature energy harvesting technologies, a key technology in facilitating the deployment of resilient wireless sensor nodes into hostile environments. The system demonstrates the capability to store an initial voltage of 2.3V decaying to 0.5V in 300ms with a Schottky based system. Replacing the Schottky diode with a switched system, a much lower decay rate to 1.5V in over 8s was observed. This shows that an effective harvester could be made with a switched power controller.