Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors

This reprint is a collection of the Special Issue "Advance in Energy Harvesters/Nanogenerators and Self-Powered Sensors" published in Nanomaterials, which includes one editorial, six novel research articles and four review articles, showcasing the very recent advances in energy-harvesting and self-powered sensing technologies. With its broad coverage of innovations in transducing/sensing mechanisms, material and structural designs, system integration and applications, as well as the timely reviews of the progress in energy harvesting and self-powered sensing technologies, this reprint could give readers an excellent overview of the challenges, opportunities, advancements and development trends of this rapidly evolving field

Study of systems powered by triboelectric generators for bioengineering applications

Treballs Finals de Grau d'Enginyeria Biomèdica. Facultat de Medicina i Ciències de la Salut. Universitat de Barcelona. Curs: 2020-2021. Director: Pere Lluís Miribel Català. Co-director: Manel Puig i Vida

Nanogenerators in Korea

Fossil fuels leaded the 21st century industrial revolution but caused some critical problems such as exhaustion of resources and global warming. Also, current power plants require too much high cost and long time for establishment and facilities to provide electricity. Thus, developing new power production systems with environmental friendliness and low-cost is critical global needs. There are some emerging energy harvesting technologies such as thermoelectric, piezoelectric, and triboelectric nanogenerators, which have great advantages on eco-friendly low-cost materials, simple fabrication, and various operating sources. Since the introduction of various energy harvesting technologies, many novel designs and applications as power suppliers and physical sensors in the world have been demonstrated based on their unique advantages. In this Special Issue, we would like to address and share basic approaches, new designs, and industrial applications related to thermoelectric, piezoelectric, and triboelectric devices which are on-going in Korea. With this Special Issue, we aim to promote fundamental understanding and to find novel ways to achieve industrial product manufacturing for energy harvesters

Roadmap on energy harvesting materials

Ambient energy harvesting has great potential to contribute to sustainable development and address growing environmental challenges. Converting waste energy from energy-intensive processes and systems (e.g. combustion engines and furnaces) is crucial to reducing their environmental impact and achieving net-zero emissions. Compact energy harvesters will also be key to powering the exponentially growing smart devices ecosystem that is part of the Internet of Things, thus enabling futuristic applications that can improve our quality of life (e.g. smart homes, smart cities, smart manufacturing, and smart healthcare). To achieve these goals, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. By bringing together the perspectives of experts in various types of energy harvesting materials, this Roadmap provides extensive insights into recent advances and present challenges in the field. Additionally, the Roadmap analyses the key performance metrics of these technologies in relation to their ultimate energy conversion limits. Building on these insights, the Roadmap outlines promising directions for future research to fully harness the potential of energy harvesting materials for green energy anytime, anywhere

Energy harvesting based on triboelectric nanogenerators (TENGs) and applications

The rapid development of technologies and great progress of society has placed serious demands on the supply of fossil fuels and ensued consequential environmental pollution. Harvesting ambient energy from the environment is regarded as an effective way to deal with this energy crisis. Recently, triboelectric nanogenerators (TENG) based on contact electrification and electrostatic induction have been demonstrated to be a novel and efficient technique for efficiently harvesting ambient mechanical energy. TENGs have the advantages of simple structure, low cost and easy fabrication, high energy conversion efficiency at low frequencies (1-10 Hz), and are suitable for applications of wearable and implantable electronics. The key to the development of TENG is the high-performance output based on small size and application as a self-powered sensor, which can be used to monitor environmental changes such as temperature and humidity. This doctoral research aims to explore new strategies to enhance the output of TENGs and to develop TENG based self-powered sensors. The research work carried out and the results obtained are summarized as follows. Firstly, although significant work has been carried out to develop materials with high surface charge density for high-performance TENG, little attention has been paid to the roles of electrode materials that are responsible for charge collection. This work reports on a facile synthesis of laser-induced graphene (LIG) as high-efficiency electrodes for TENGs. Tribo-negative polyimide (PI) and tribo-positive cellulosic paper were converted into PI-LIG and paper-LIG, respectively, by a direct photothermal process using a conventional CO2 laser. The LIG-based TENGs showed higher electrical output characteristics with a peak-to-peak voltage of up to ~625 Vp-p, a current density of ~20 mA.m-2 and a transferred charge density of ~138 μC.m-2 with a maximum power output of ~2.25 W.m-2 , respectively, while the corresponding values for the conventional Al-tape electrode-based paper-PI TENGs were 400 Vp-p, ~10 mA.m-2 , ~85 μC.m-2 and 0.9 W.m-2 , respectively. The mechanically robust LIG electrodes show excellent stability with less than 5.0% variation in output over 12,000 contact cycles. Kelvin probe force microscopy (KPFM) measurements confirmed that the average surface potentials of the LIG triboelectric surfaces are smaller than those of the pristine ones, indicating the role of initial surface chemistry in the formation of LIGs and the performance of TENG. The performance enhancement for LIG-based TENGs is ascribed to the lowering of the charge transfer barrier energy which results in a higher surface charge of the dielectric layer, and the significantly (~ 6 orders) lower contact impedance of LIG electrodes. Thus, via the removal of the additional interface between the triboelectric surface and electrode, high-performance metal-free TENGs with excellent prospects for enabling energy harvesting applications can be realised. Secondly, a TENG based on the polarization effect of piezoelectric nanomaterials working together with the piezoelectric and triboelectric effects was proposed as a new strategy. The polarization effect of piezoelectric material can provide a higher surface charge to the friction layer. For this, a variety of ZnO materials with different nanostructures were prepared and applied to TENGs to compare the effect of the effective contact area on the output performance of TENGs. Compared with the pristine PDMS-based TENG, the outputs of the five ZnO-PDMS TENG with different nanostructures have been significantly improved. The TENG with disk-like nanostructure ZnO-PDMS shows the highest peak output of ~780Vp-p, which is 136% higher than the pristine PDMS-based TENG (~330Vp-p). Correspondingly, the short-circuit current density and charge density has been increased by 205% and 114%, respectively. The nanoflowers nanostructure showed the lowest peak output of ~470Vp-p, which was 42% higher than the pristine PDMS TENG. Correspondingly, the short-circuit current density and charge density rose by 62% and 28%, from 52 mA.m-2 to 84 mA.m-2 , and from ~80 μC.m-2 to ~102 μC.m-2 , respectively. The enhancement produced by the disk-like ZnO nanostructures arose from the increase in the surface contact area in the vertical direction to the greatest extent. Furthermore, the surface charge enhancement and distribution of ZnO with different nanostructures were demonstrated by the piezoelectric microscopy (PFM). Finally, utilizing wide absorption characteristics of a narrow bandgap (~1.8 eV) semiconductor, we report on Bismuth Oxyiodide (BiOI) based photo-enhanced TENG. The tribo-positive BiOI film deposited electrochemically on transparent Fluorine doped Indium Tin Oxide (FTO) substrate provided a way to exploit concurrently the photo-enhanced charge generation and triboelectric effects. When utilized against tribo-negative PDMS films, under illumination, the BiOI/PDMS TENGs’ outputs were significantly enhanced, wherein an increase of 21% in peak to peak output voltage (from 59Vp-p to 73Vp-p, 38% in charge density (from 40µC.m-2 to 55µC.m-2 ), and 74% in overall power density (from 0.25 W.m-2 (in dark) and 0.44 W.m-2 (under illumination)), respectively, were observed. Correspondingly, a dramatic enhancement (from ~25 mV to ~300 mV) in the average surface potential, termed as surface photovoltage (SPV), for the illuminated BiOI was observed by KPFM. For an isolated, grounded BiOI/FTO electrode, this SPV increase is slow-decaying (~3.5 h) and is attributed to the high dielectric constant, presence of deep-traps within BiOI, and slow charge-exchange with the ambient environment. The work thus not only provides an approach for the enhancement of mechanical-to-electrical efficiency of TENGs by light absorption, but also can be utilized for self-powered detection of electromagnetic radiation and photodetectors. All the high-performance TENGs produced have the potential to be used in the realisation of self-powered systems and can be of great significance as a new alternative energy harvesting source

Two-Dimensional Nanomaterials and Nanocomposites for Sensing, Separation, and Energy Applications

Two-dimension (2D) nanomaterials have gained popularity for the last few decades due to their excellent mechanical, electrical and thermal properties. These unique properties of 2D nanomaterials can be exploited in various applications specially in sensor, energy, and separation devices. In this study, the sensing and energy generation performance of PVDF/PAni fiber mat systems made by the forcespinning method with and without graphene coating. The graphene-coated nanocomposites show an average output voltage of 75 mV (peak-to-peak) which is 300% higher compared to bare fiber mats and an output current of 24 mA (peak-to-peak) by gentle finger pressing. Moreover, the graphene-coated PVDF/PAni was investigated as a promising system for temperature (5 times better sensitivity), vibration (2 times better voltage generation), and airflow sensing. The graphene-coated composite has been further investigated as a water tide energy harvesting piezoelectric nanogenerator, the system generates ~ 40 mV for a synthetic ocean wave with a flow rate of 30 mL/min. Additionally, fabricated a low-cost, single-step, sophisticated graphene-enhanced elastomeric nanocomposite sensor for multifunctional usage by using a batch mixer. This nanocomposite ink was then fabricated into flexible keypad & forecepad and separation devices. Furthermore, the study also showed the enhanced battery performance of chemical vapor deposited pyrolytic carbon coatings on nanoparticles and nanofibers

Optimisation-driven design of sliding mode triboelectric energy harvesters

With the increasing demand of emerging technologies for autonomous sensing, the modelling and optimisation of complete energy harvesting systems are essential to achieve efficient power output. To date, most of the optimisation efforts in enhancing the performance of triboelectric energy harvesters have been focused on the improvement of material properties and on the establishment of figures of merit to assist in the definition of parameters. However, these efforts do not consider the complex relationship between the device structure and power output, physical constraints in place, and varying excitation conditions. This paper fills that gap for the first time by applying an optimisation algorithm to establish mechanisms for optimisation-driven design of sliding-mode triboelectric energy harvesters. A global optimisation methodology is developed to improve its performance, having experimentally validated the numerical model adopted. This work highlights the need for a more robust design framework for applications of triboelectric energy harvesting and proposes a hybrid approach combining the finite element method with analytical models to consider different energy harvesting parameters including the degradation of the charge transfer efficiency due to the edge effect. A novel high-power output sliding-mode triboelectric energy harvesting concept is proposed and its performance is optimised, using the proposed methodology

Vibration Energy Harvesting for Wireless Sensors

Kinetic energy harvesters are a viable means of supplying low-power autonomous electronic systems for the remote sensing of operations. In this Special Issue, through twelve diverse contributions, some of the contemporary challenges, solutions and insights around the outlined issues are captured describing a variety of energy harvesting sources, as well as the need to create numerical and experimental evidence based around them. The breadth and interdisciplinarity of the sector are clearly observed, providing the basis for the development of new sensors, methods of measurement, and importantly, for their potential applications in a wide range of technical sectors