Waste Thermal Energy Harvesting Research Articles

2D‐Pyroelectric Materials for Waste Thermal Energy Harvesting and Beyond

AbstractPolar 2D materials hold the emerging functionalities such as ferro‐, piezo‐, and pyro‐electric properties. On account of infrared‐active low bandgap and polar nature at reduced dimensionality, they served as an ideal choice of pyroelectric material. It can cover up a diverse range of applications, such as waste thermal energy harvesting, IR imaging, photodetector, temperature sensors, and several catalytic processes due to the abundance of dynamic thermal fluxes. Recently, 2D pyroelectric materials have manifested a substantial role in thermal energy harvesting. Consequently, it is realized that there are plenty of scopes available to diversify its applicability. Thus, the challenges are spotlighted in this perspective to envision the desired 2D pyroelectric materials to achieve the effective thermal energy harvesting, sensing, and catalytic efficacy. Particularly, the emphasis is given to elucidate the role of spontaneous polarization in 2D materials to ascertain the giant pyroelectricity.

Thermoelectric Energy Harvesting from Single-Walled Carbon Nanotube Alkali-Activated Nanocomposites Produced from Industrial Waste Materials.

A waste-originated one-part alkali-activated nanocomposite is introduced herein as a novel thermoelectric material. For this purpose, single-walled carbon nanotubes (SWCNTs) were utilized as nanoinclusions to create an electrically conductive network within the investigated alkali-activated construction material. Thermoelectric and microstructure characteristics of SWCNT-alkali-activated nanocomposites were assessed after 28 days. Nanocomposites with 1.0 wt.% SWCNTs exhibited a multifunctional behavior, a combination of structural load-bearing, electrical conductivity, and thermoelectric response. These nanocomposites (1.0 wt.%) achieved the highest thermoelectric performance in terms of power factor (PF), compared to the lower SWCNTs’ incorporations, namely 0.1 and 0.5 wt.%. The measured electrical conductivity (σ) and Seebeck coefficient (S) were 1660 S·m−1 and 15.8 µV·K−1, respectively, which led to a power factor of 0.414 μW·m−1·K−2. Consequently, they have been utilized as the building block of a thermoelectric generator (TEG) device, which demonstrated a maximum power output (Pout) of 0.695 µW, with a power density (PD) of 372 nW·m−2, upon exposure to a temperature gradient of 60 K. The presented SWCNT-alkali-activated nanocomposites could establish the pathway towards waste thermal energy harvesting and future sustainable civil engineering structures.

Strain-induced electronic, stability and enhancement of thermoelectric performance of 2D Si2C3 monolayer: An emerging material for renewable energy

Strain engineering is a highly efficient technique to improve the electronic, mechanical, and thermoelectric characteristics of two-dimensional materials. Inspired by a recent study on the most stable structures of the silicon-carbon monolayer [Li. P. et al., Nanoscale, 2014, 11685], we have carried out systematic investigations for 2D Si2C3 monolayer (ML) on electronic, dynamical, mechanical, thermal stability and thermoelectric properties by applying the biaxial tensile strain using density functional theory combined with semi-classical Boltzmann transport theory. The calculated results demonstrate that biaxial tensile strain can change the position of the conduction band minimum (CBM) or valence band maximum (VBM), which produce significant effects in the thermometric parameters. The enhanced power factor strongly suggests that biaxial tensile strain is a compelling way to improve the thermoelectric (TE) performance of 2D Si2C3 ML, making it an ideal candidate for thermoelectric applications. Such strain sensitive thermoelectric response in 2D Si2C3 ML couldopen pathways for a wide range of applications in the emerging renewable energy such as thermoelectric power generation and waste thermal energy harvesting.

Study of Fiber-Based Wearable Energy Systems.

Fiber-based electronic and photonic devices have the most desired human-friendly features, such as being soft, ubiquitous, flexible, stretchable, light, and permeable, and thus are ideal to be employed as the interface platform between humans, the environment, and machines. Today, these smart wearable devices are normally powered by rechargeable batteries. It is extremely desirable to have an undisrupted power supply for us to go anywhere at any time. Harvesting energy from the ambient environment or our body can potentially fulfill such a goal. Explorations of high performance, flexible functional materials and energy conversion devices have led many exiting discoveries. In order to realize their applications, equally important are fundamental studies of the physical phenomena and mechanisms that will provide scientific guidance for the direction of exploration and development of devices and systems. Hence, this Account provides a brief review of our recent progress in this topic area. Based upon materials science, mechanics and device physics, we have succeeded in establishment of several new theoretical models for fiber-based piezoelectric, triboelectric, and hybrid generators. These models have been verified experimentally. Excellent results were obtained for fiber-based triboelectric generators without any adjustable parameters. Reasonable agreement was demonstrated for the piezoelectric generators because of some uncertainty in the material properties and deformation modes. From both simulated and experimental results, we did not detect any synergic effect in the hybrid generator consisting of cascaded piezoelectric and triboelectric units. The verified models can be used to predict the output voltage, current, and power of the devices in terms of material properties, parameters of device structure, harvesting circuits, and operating conditions. Furthermore, by considering the electric breakdown due to field-induced-emission and gas-ionization, we have identified the theoretical upper limits of charge density and output power from contact-mode fiber-based triboelectric nanogenerators. The analysis sheds new light on the scope and focus for further exploration and provides guidance on engineering design of such devices. In addition, we have setup an experimental platform for reliable triboelectric charge measurement of highly deformable and porous materials like fabrics. An extended triboelectric series has been reported by us including 21 types of commercial and new fibers. Based upon the findings, we have made significant improvements of the performance of these energy harvesting devices. Finally, we have explored a class of new flexible thermoelectric materials exhibiting high performance for fiber-based thermoelectric generators, which can be fabricated by low-temperature and cost-effective processes, such as in situ reduction coating and three-dimensional printing. The resultant large-area, flexible, and wearable fiber-base thermoelectric generators are key devices for great potential applications such as powering wearable microelectronic systems, active microclimate regulating systems, and waste thermal energy harvesting.

Compressive strain induced enhancement in thermoelectric-power-factor in monolayer MoS2 nanosheet

Strain and temperature induced tunability in the thermoelectric properties in monolayer MoS2 (ML-MoS2) has been demonstrated using density functional theory coupled to semi-classical Boltzmann transport theory. Compressive strain, in general and uniaxial compressive strain (along the zig-zag direction), in particular, is found to be most effective in enhancing the thermoelectric power factor, owing to the higher electronic mobility and its sensitivity to lattice compression along this direction. Variation in the Seebeck coefficient and electronic band gap with strain is found to follow the Goldsmid–Sharp relation. n-type doping is found to raise the relaxation time-scaled thermoelectric power factor higher than p-type doping and this divide widens with increasing temperature. The relaxation time-scaled thermoelectric power factor in optimally n-doped ML-MoS2 is found to undergo maximal enhancement under the application of 3% uniaxial compressive strain along the zig-zag direction, when both the (direct) electronic band gap and the Seebeck coefficient reach their maximum, while the electron mobility drops down drastically from 73.08 to 44.15 cm2 V−1 s−1. Such strain sensitive thermoelectric responses in ML-MoS2 could open doorways for a variety of applications in emerging areas in 2D-thermoelectrics, such as on-chip thermoelectric power generation and waste thermal energy harvesting.

Harvesting thermal energy (via radiation) using pyroelectric materials (PZT-5H): An experimental study

ABSTRACTThe field of waste thermal energy harvesting has experienced significant growth over the past few years. This paper presents an experimental study on thermal radiation to electrical energy conversion using pyroelectric material (PbZrxTi1-xO3 (PZT-5H)). Pyroelectric material was exposed to UV lamp with a constant frequency of 0.5 Hz and another surface of sample was continuously cooled via natural air fan (for generation continuous temporal gradient in material). Maximum value of stored energy was 1.75 µJ across 100 µF without load resistance. Maximum power output was found to be 0.76 µW across load resistance of 3 MΩ and 10 µF.

Pyroelectric Energy Harvesting Using (Ba0.85Ca0.15) (Zr0.1Ti0.89Fe0.01)O3 Ceramics

There has been a significant increase in the research on waste thermal energy harvesting in recent years. This paper describes harvesting thermal energy using (Ba0.85Ca0.15) (Zr0.1Ti0.89Fe0.01)O3 (BCZTO-Fe) pyroelectric ceramics. The poled sample was placed in front of hot and cold blowers alternatively in order to have continuous electric signal. A simple electrical circuit consists of full wave rectifier with different value of capacitor and load resistance was connected to the pyroelectric material. Maximum value of stored energy was 3.9μJ at 47μF without load resistance. Maximum power output was found to be 106nW across load resistance of 5MΩ and 10 μF.

Large and Tunable Photothermoelectric Effect in Single-Layer MoS2

We study the photoresponse of single-layer MoS(2) field-effect transistors by scanning photocurrent microscopy. We find that, unlike in many other semiconductors, the photocurrent generation in single-layer MoS(2) is dominated by the photothermoelectric effect and not by the separation of photoexcited electron-hole pairs across the Schottky barriers at the MoS(2)/electrode interfaces. We observe a large value for the Seebeck coefficient for single-layer MoS(2) that by an external electric field can be tuned between -4 × 10(2) and -1 × 10(5) μV K(-1). This large and tunable Seebeck coefficient of the single-layer MoS(2) paves the way to new applications of this material such as on-chip thermopower generation and waste thermal energy harvesting.

Investigation of a MEMS-based capillary heat exchanger for thermal harvesting

This article describes theoretical and experimental studies of MEMS-based capillary heat exchangers, designed for use as the heat sink in a waste thermal energy harvesting system currently under development. Specific goals include the understanding of the impact of thermal conductivity and capillary dimensions. Experimental studies were done using silicon and SU-8 based heat exchangers each with rectangular capillaries having width of 100μm. The depth of silicon capillaries was maintained at either 64 or 100μm while that of SU-8 capillaries was varied from 48 to 134μm to 160 to 375μm. The overall footprint of each microdevice was 38mm by 13mm. The fluid used was 3M™ HFE 7200. Heat exchanger performance was characterized based on operating temperature, mass transfer rate, heat flux, and thermal resistance. Studies were done for two different operating temperatures, one below the boiling point and another at the boiling point of the working fluid. These two operating temperatures were referred to in this article as low-temperature and high-temperature operation mode. Based on the experimental study the fluid was found to wet both silicon and SU-8 with contact angle measured to be 6°. From the experimental studies conducted it was found that the pumping effect of the capillaries increased with increasing wall height. Based on the thermal tests it was observed that the highest mass transfer rate and heat flux under the low-temperature and high-temperature operation mode were obtained for an SU-8 heat exchanger with capillary height of 134μm and silicon heat exchanger with capillary height of 100μm, respectively. Based on this study it was found that under low-temperature operation mode the capillary dimension was more influential than thermal conductivity; however, under high-temperature operation mode the opposite was proved to be the case. The thermal resistances were found to vary from 0.011 to 0.09m2CW and from 0.0073 to 0.0096m2CW for low-temperature and high-temperature operation mode respectively. Also it was found based on comparison that the conceptualized MEMS-based capillary heat exchanger was found to have lower thermal resistance than existing heat sinks. Using the experimentally validated theoretical model developed in this work it was found that the performance of the MEMS-based capillary heat exchangers improved with increasing thermal conductivity of the substrate as well as the capillary dimensions. The model has helped conclude that developing SU-8 capillaries on aluminum or copper substrates would optimize the influence of thermal conductivity and capillary dimensions on the performance of the MEMS-based heat exchanger.

Waste thermal energy harvesting from a convection-driven Rijke–Zhao thermo-acoustic-piezo system

In this work, a convection-driven Rijke–Zhao thermo-acoustic-piezo system is designed and experimentally tested to demonstrate its potential for harvesting thermal energy. For this, a nonlinear theoretical model is developed to simulate the energy conversion process, i.e. heat-to-sound-to-electricity in the present system. Unlike the conventional conduction-driven thermoacoustic converters, our present system involves no heat exchangers and stacks. As a heat source is placed in a Rijke–Zhao tube with two bifurcating daughter branches, self-sustained thermoacoustic oscillations are generated. The resulting acoustic fields in the bifurcating branches are dramatically different. One branch is associated with ‘hot’ oscillations. However the other is with ‘cold’ oscillations at ambient temperature, which enable a piezoelectric generator being implemented to the end of the branch. In order to measure the acoustic fields in the bifurcating branches, two arrays of thermocouples and microphones are used. The maximum sound pressure level is around 139dB. The output electric power and acoustical energy conversion efficiency are measured and compared with that from a similar but a conduction-driven thermo-acoustic-piezo system. It is found that 60% more power is generated. And the energy conversion efficiency is increased by 105%. These experimental results confirm that the developed Rijke–Zhao thermo-acoustic-piezo system is an invaluable tool in designing a simple, low-cost, energy-efficient thermoacoustic system.