Compositionally Graded Organic–Inorganic Nanocomposites for Enhanced Thermoelectric Performance

AbstractThermoelectric generators (TEGs) operate in the presence of a temperature gradient, where the constituent thermoelectric (TE) material converts heat into electricity via the Seebeck effect. However, TE materials are characterized by a thermoelectric figure of merit (ZT) and/or power factor (PF), which often has a strong dependence on temperature. Thus, a single TE material spanning a given temperature range is unlikely to have an optimal ZT or PF across the entire range, leading to inefficient TEG performance. Compositionally graded organic–inorganic nanocomposites are demonstrated, where the composition of the TE nanocomposite can be systematically tuned along the length of the TEG, in order to optimize the PF along the applied temperature gradient. The nanocomposite composition is dynamically tuned by an aerosol‐jet printing method with controlled in situ mixing capability, thus enabling the realization of such compositionally graded thermoelectric composites (CG‐TECs). It is shown how CG‐TECs can be realized by varying the loading weight percentage of Bi2Te3 nanoparticles or Sb2Te3 nanoflakes within an organic conducting matrix using bespoke solution‐processable inks. The enhanced energy harvesting capability of these CG‐TECs from low‐grade waste heat (&lt;100 °C) is demonstrated, highlighting the improvement in output power over single‐component TEGs.</jats:p

Piezoelectric Semiconducting Nanowires

© 2018 Elsevier Inc. Piezoelectric semiconducting nanowires have generated much interest due to the interplay of their mechanical, electrical, and optical properties, which paves the way for potential applications in mechanical energy harvesting as well as sensing. The nature of piezoelectricity in these nanowires is governed by the crystalline phases present, which in turn can be controlled during the nanowire growth process. This chapter provides insight into the manifestation of piezoelectricity in semiconducting nanowires, the effect of growth on their piezoelectric properties, and importantly, how piezoelectricity is characterized at the nanoscale in these materials. Energy-related applications of semiconducting piezoelectric nanowires are described in detail, including their incorporation into nanogenerators for energy harvesting, as well as in piezotronic and photo-piezotronics devices based on the electromechanical and opto-electromechanical interactions taking place in piezoelectric semiconductor-nanowire junction-based devices. Advances in nanofabrication, nanoscale characterization, and device engineering, coupled with a greater understanding and control of piezoelectricity in semiconducting nanowires, will ultimately help unlock the full potential of these fascinating nanomaterials.European Research Council (Grant no. ERC–2014–STG–639526, NANOGEN

Enhanced thermoelectric properties of flexible aerosol-jet printed carbon nanotube-based nanocomposites

Aerosol-jet printing allows functional materials to be printed from inks with a wide range of viscosities and constituent particle sizes onto various substrates, including the printing of organic thermoelectric materials on flexible substrates for low-grade thermal energy harvesting. However, these materials typically suffer from relatively poor thermoelectric performance, compared to traditional inorganic counterparts, due to their low Seebeck coefficient, S, and electrical conductivity, σ. Here, we demonstrate a modified aerosol-jet printing technique that can simultaneously incorporate well dispersed high S Sb2Te3 nanoflakes, and high-σ multi-walled carbon nanotubes (MWCNTs) providing good inter-particle connectivity, to significantly enhance the thermoelectric performance of poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) structures on flexible polyimide substrates. A nominal loading fraction of 85 wt.% yielded a power factor of ~41 µW/mK2, which is among the highest for printed organic-based structures. Rigorous flexing and fatigue tests were performed to confirm the robustness and stability of these aerosol-jet printed MWCNT-based thermoelectric nanocomposites

Observation of Confinement-Induced Self-Poling Effects in Ferroelectric Polymer Nanowires Grown by Template Wetting

Ferroelectric polymer nanowires grown using a template-wetting method are shown to achieve an orientated 'self-poled' structure resulting from the confined growth process. Self-poling is highly desirable as it negates the need for high electric fields, mechanical stretching and/or high temperatures typically associated with poling treatments in ferroelectric polymers, as required for piezoelectric and/or pyroelectric applications. Here, we present differential scanning calorimetry, infrared spectroscopy and dielectric permittivity measurements on as-fabricated template-grown polyvinylidene fluoride-trifluoroethylene (P(VDF-TrFE)) nanowires, and quantitatively compare the results with spin-cast films of the same composition that have been electrically poled, both before and after subsequent de-poling temperature treatment. The measurements reveal remarkably similar trends between the physical properties of the as-grown nanowires and the electrically poled film samples, providing insight into the material structure of the 'self-poled' nanowires. In addition, piezo-response force microscopy (PFM) data is presented that allow s for unambiguous identification of self-poling in ferroelectric polymer nanostructures, and indicates the suitability of the template-wetting approach in fabricating nanowires that can be used directly for piezoelectric/pyroelectric applications, without the need for post-deposition poling/processing.The authors are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant no. ERC-2014-STG-639526, NANOGEN). R.A.W. thanks the EPSRC Cambridge NanoDTC, EP/G037221/1, for studentship funding.This is the author accepted manuscript. It is currently under an indefinite embargo pending publication by Wiley

Designing of Next Generation Motor Drive Control for Electric Vehicle Application

In order to achieve a mission of zero emission, as most automotive industries around the world are pledging to, the research and production of efficient and eco-friendly electrified vehicles (EVs) is a necessary goal to pursue. They are of high interest to governments and research facilities across the world as they have higher efficiency levels and are more environmentally friendly than current gasoline vehicles. At the core of electric vehicle application, electric motor drives act an important role to direct the motor to convert electrical energy into mechanical energy and provide electrical control of the processes. Therefore, it is required for researchers to make the motor drive more energy-efficient and have bi-directional power flow capability to ensure the improvement of motor performance and be flexible regarding controllability. The goal of the author is to investigate the development of a better motor-drive to achieve a control that provides a superior control of the traction motor. This requires improving the existing flux weakening motor control that is used for traction application. The improved control is programmed and hard coded into a Digital signal processor which is embedded in the control drive board. In a conventional inverter, this drive unit controls the gate drivers which in turn controls the IGBTs, there by enabling variation in operating performance of the motor. Currently, there is a lack of unified program that can operate any kind of traction motor like permanent magnet synchronous motors (PMSM) or induction motors(IM). This is leading automotive industries to invest a lot of resources in research and development in this field of work so that the future vehicles can be swapped with any motor as per requirement. The authors are currently working on developing this motor control and also reducing the complexity of the code and real-time operation on the microcontroller. This will be implemented in future on existing and new-generation inverters to test the control on various motor and inverter setups

Freestanding Functional Structures by Aerosol-Jet Printing for Stretchable Electronics and Sensing Applications

The requirements for modern electronic devices, particularly those intended for wearable or human health monitoring applications, have rapidly evolved to being both flexible and stretchable. Hence devices, as well as interconnects, need to be capable of retaining functionality even when being mechanically deformed. Most approaches towards achieving this rely on printing or transferring structures onto elastomeric substrates that can withstand stretching. However, the processing involved can often be cumbersome, and the structures themselves tend to suffer from poor fatigue and/or are limited by the mechanical properties of the underlying substrate. Here, we introduce an aerosol-jet printing technique by which fully freestanding functional structures can be built up layer by layer, which are stable and robust upon repeated stretching. The process involves printing a combination of layers of different materials with the desired functionality, onto a substrate coated with a sacrifical film that is subsequently dissolved to release the printed structure. Using this method, we demonstrate freestanding conductive wires can be used as stretchable interconnects/electrodes, and that also function as strain-sensors. We also show that a freestanding capacitive structure functions as a robust, stretchable humidity sensor, paving the way for the development of other multi-layer, multifunctional stretchable devices and sensors

Aerosol-Jet Printed Fine-Featured Triboelectric Sensors for Motion Sensing

Triboelectric motion sensors, based on the generation of a voltage across two dissimilar materials sliding across each other as a result of the triboelectric effect, have generated interest due to the relative simplicity of the typical grated device structures and materials required. However, these sensors are often limited by poor spatial and/or temporal resolution of motion due to limitations in achieving the required device feature sizes through conventional lithography or printing techniques. Furthermore, the reliance on metallic components that are relatively straightforward to pattern into fine features limits the possibility to develop transparent sensors. Polymers would allow for transparent devices, but these materials are significantly more difficult to pattern into fine features when compared to metals. Here, we use an aerosol-jet printing (AJP) technique to develop triboelectric sensors using a wide variety of materials, including polymers, which can be directly printed into finely featured grated structures for enhanced sensitivity to displacement and speed of motion. We present a detailed investigation highlighting the role of material selection and feature size in determining the overall resolution of the resulting motion sensor. A 3-channel rotary sensor is also presented, demonstrating the versatility of the AJP technique in developing more complex triboelectric motion sensors.European Research Council (ERC-2014-STG-639526, NANOGEN) Marie Sklodowska Curie Fellowship (H2020-MSCA-IF-2015-702868

Linear anhysteretic direct magnetoelectric effect in Ni0.5Zn0.5Fe2O4/poly(vinylidene fluoride-trifluoroethylene) 0-3 nanocomposites

Free-standing flexible magnetoelectric 0-3 composite films, comprising Ni0.5Zn0.5Fe2O4 (NZFO) ferrite nanoparticles in a poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] copolymer matrix, have been prepared at low temperatures by solvent casting and melt crystallization. Ferroelectric, piezoelectric, magnetic and direct magnetoelectric properties of the nanocomposites depend strongly on ferrite concentration. Magnetoelectric voltage coefficients increase linearly with applied dc magnetic-bias fields up to 5 kOe and show no hysteresis. At this field, a maximum magnetoelectric voltage coefficient of 1.35 mV cm 1 Oe 1 was obtained for samples with 15 wt. % ferrite using a 40 kHz resonant signal.FEDER “Programa Operacional Factores de Competitividade – COMPETE” (NANO/NMed-SD/0156/2007)Fundação para a Ciência e a Tecnologia (FCT) - (PTDC/CTM/69316/2006), (SFRH/BD/45265/2008)Engineering and Physical Sciences Research Council (EPSRC

Controlling and assessing the quality of aerosol jet printed features for large area and flexible electronics

Aerosol jet printing (AJP) is a versatile technique suitable for large-area, fine-feature patterning of both rigid and flexible substrates with a variety of functional inks. In particular, AJP can tolerate ink viscosities between 1 and 1000 cP, with printing resolution of the order of 10 μm, thus making it attractive for flexible and printed electronics. This work investigates in detail significant aspects of ink-substrate combination and substrate temperature that are highly relevant to AJP. In order to do this, thin conducting silver lines are printed using AJP on both rigid (glass and silicon) as well as flexible (polyimide) substrates. The correlation between the various deposition parameters and the 'quality' of the printed lines are evaluated, through measurements of electrical conductivity under different experimental conditions. Based on our findings, a framework is proposed through which the morphology of AJP lines can be controlled and assessed for applications in large area and flexible electronic devices.SK-N, MS and YSC are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant No. ERC-2014-STG-639526, NANOGEN). MS and YSC acknowledge studentship funding from the Cambridge Commonwealth, European & International Trust. CB thanks the EPSRC Cambridge NanoDTC, EP/G037221/1, for studentship funding

Template-Assisted Hydrothermal Growth of Aligned Zinc Oxide Nanowires for Piezoelectric Energy Harvesting Applications.

A flexible and robust piezoelectric nanogenerator (NG) based on a polymer-ceramic nanocomposite structure has been successfully fabricated via a cost-effective and scalable template-assisted hydrothermal synthesis method. Vertically aligned arrays of dense and uniform zinc oxide (ZnO) nanowires (NWs) with high aspect ratio (diameter ∼250 nm, length ∼12 μm) were grown within nanoporous polycarbonate (PC) templates. The energy conversion efficiency was found to be ∼4.2%, which is comparable to previously reported values for ZnO NWs. The resulting NG is found to have excellent fatigue performance, being relatively immune to detrimental environmental factors and mechanical failure, as the constituent ZnO NWs remain embedded and protected inside the polymer matrix.The authors thank Yeonsik Choi for discussions and experimental support. S.K.-N., C.O., and A.D. are grateful for financial support from the European Research Council through an ERC Starting Grant (Grant no. ERC-2014-STG-639526, NANOGEN). F.L.B. and R.A.W. thank the EPSRC Cambridge NanoDTC, EP/G037221/1, for studentship funding. P.S.J. acknowledges the support of TEP-1900 and Talentia Postdoc Program, cofunded by the European Union’s Seventh Framework Program, Marie Skłodowska-Curie actions (COFUND Grant Agreement 267226) and the Ministry of Economy, Innovation, Science and Employment of the Junta de Andalucía. S-L.S acknowledges support through the EPSRC grant EP/M010589/1This is the final version of the article. It first appeared from American Chemical Society via http://dx.doi.org/10.1021/acsami.6b04041