Optimisation of Triboelectric Nanogenerator performance in vertical contact-separation mode

Triboelectric nanogenerator (TENG) is one of the most promising energy harvesters – a technology that uses repeated or reciprocating contact of suitably chosen materials to generate charge via the triboelectric effect (TE) and utilizes this as usable voltage and current. TENGs are attractive as they can continuously generate charge over a wide range of operating conditions and have several valuable advantages such as light weight, simple structure, low cost and high efficiency. Therefore, TENGs have been explored in a wide range of applications, including self-powered wearable electronics, powering electronics and even for harvesting ocean wave/wind energy. One of the major limitations of TENGs is their low power output (usually <500 W/m2). This thesis focuses of a few specific approaches to optimising TENG output performance. This thesis begins by presenting a solution to this challenge by optimizing a low permittivity substrate beneath the tribo-contact layer. The open circuit voltage is found to increase by a factor of 1.3 in moving from PET to the lower permittivity PTFE. TENG performance is also believed to depend on contact force, but the origin of the dependence had not previously been explored. Herein, we show that this behaviour results from a contact force dependent real contact area Ar as governed by surface roughness. The open circuit voltage Voc, short circuit current Isc and Ar for a TENG were found to increase with contact force/pressure. Critically, Voc and Isc saturate at the same contact pressure as Ar suggesting that electrical output follows the same evolution as Ar. Assuming that tribo charges can only transfer across the interface at areas of real contact, it follows that an increasing Ar with contact pressure should produce a corresponding increase in the electrical output. These results underline the importance of accounting for real contact area in TENG design, as well as the distinction between real and nominal contact area in tribo-charge density definition. High-performance ferroelectricassisted TENGs (Fe-TENGs) are developed using electrospun fibrous surfaces based on P(VDFTrFE) with dispersed BaTiO3 (BTO) nanofillers in either cubic (CBTO) or tetragonal (TBTO) form in this thesis. TENGs with three types of tribo-negative surface were investigated and output increased progressively. Critically, P(VDF-TrFE)/TBTO produced higher output than P(VDFTrFE)/ CBTO even though permittivity is nearly identical. Thus, it is shown that BTO fillers boost output, not just by increasing permittivity, but also by enhancing the crystallinity and amount of the β-phase (as TBTO produced a more crystalline β-phase present in greater amounts)

Enhanced Triboelectric Nanogenerator Performance via an Optimised Low Permittivity, Low Thickness Substrate

With electrical power generated from mechanical contact, the triboelectric nanogenerators (TEN Gs) have attracted attention recently as a promising route to realising self-powered sensors (e.g. tactile sensors, biomedical sensors etc.). Due to their limited power range (0.1-100 mW/cm 2 ), it is important to optimise the output performance of TENGs. Among the factors that confer higher performance are materials with a strong triboelectric effect and materials with low permittivity. It can be difficult to realize these two benefits in a single contact material. This paper presents a solution to this challenge by optimising a low permittivity substrate beneath the tribo-contact layer. Results are simulated over a range of both substrate permittivity and thickness. The open circuit voltage is found to increase by a factor of 1.8 in moving from PVDF to the lower permittivity PTFE and by a further factor of 37.2 when the substrate thickness is reduced from 200 to \pmb1 μm. For PTFE with \pmb1 μm thickness, this amounts to 12.2 kV, as against 327V known from simulations up to now. These results clearly indicate that optimized low permittivity, low thickness substrates represent a potential route to self-powered sensors

A unified contact force-dependent model for triboelectric nanogenerators accounting for surface roughness

Triboelectric nanogenerators (TENGs) allow generation of electricity based on charge transfer during repeated contact of suitably chosen surfaces. Recently, rapid advances have been made in boosting their performance, but advancement in fundamental understanding has progressed more slowly. Currently, the most popular TENG models assume idealized flat surfaces that guarantee complete contact and a contact force (or load)-independent response. However, all real surfaces possess some level of surface roughness which is known to produce a load-dependent contact area. We develop a new unified model (for dielectric-to-dielectric TENGs) which adds consideration of surface roughness to the established distance-dependent electric field model. We account for surface roughness by applying Persson's contact theory to determine the load-dependent contact area. The model is applicable from first touch to nearly complete contact provided deformation remains elastic. Compared to load-independent approaches, the presented model is a better predictor of TENG performance. It captures the load-dependent nature of TENG performance apparent in recent tests. It predicts that the electrical output can be expected to be tiny at low contact loads, but should converge to an upper-bound at higher loads as the contact area approaches complete contact. Comparison with test results reveal substantially better prediction of open circuit voltage compared to load-independent models which tend to overestimate considerably. By assisting the designers with better predictions of TENG output, the developed unified theory has huge potential for advancing the use of TENGs in applications such as wearables (i.e. low loads) to tidal or wave energy (i.e. large loads)

Kirigami and mogul-patterned ultra-stretchable high-performance ZnO nanowires-based photodetector

Wearable UV photodetectors (PDs) have attracted interest recently for detection of excess exposure of the skin to the UV radiation. Despite numerous advances made in this direction, many challenges remain, particularly in terms of device reliability under extreme mechanical deformations simultaneously and self-powering, etc. Herein, a self-powered stretchable PD developed with kirigami-inspired honeycomb-patterned zinc oxide (ZnO) nanowires (NWs) and coupled with a triboelectric nanogenerator (TENG) is presented. After studying in detail the influence of ZnO NWs dispersion medium and metal-ZnO NWs contacts, a novel fabrication approach employing the structural engineering on NWs-elastomer composite is used to achieve high stretchability. The fabricated ZnO NWs-based UV PDs, embedded inside kirigami-inspired honeycomb-patterned elastomeric substrate, exhibit unprecedented stretchability (up to 125%) and high-performance with photo/dark current ratio of ≈5 × 105, responsivity of ≈54 A W−1, and a fast recovery time of 100 ms. Further, the stretchable PD is coupled with flexible TENGs to demonstrate a self-powered system for potential application in real-time UV radiation monitoring using advanced wearable healthcare technology

Aligned PLLA electrospun fibers based biodegradable triboelectric nanogenerator

Transient triboelectric nanogenerators (TENGs) fabricated with degradable materials is an emerging area which can tackle the global issue of electronic waste. Here, we report a fully biodegradable TENG comprising of aligned PLLA (aPLLA) fibres and chitosan as the active layers. The aPLLA and random PLLA (rPLLA) fibers are compared for the performance and the aPLLA fibre based TENG (aPL-TENG) is found to exhibit superior performance (output voltage and current of 45 V and 9 μA, respectively) due to better 103 helix chain conformation. The performance of aPLLA fibres was also analysed with different interface combinations. The aPL-TENG showed excellent mechanical stability for 24000 cycles and produced an output power density of 6.5 mW m−2. The soil burial test confirms the degradation of the materials used in the device fabrication. Finally, as a proof-of-concept, the output of aPL-TENG was fed to a capacitor to demonstrate it capability to continuously power the commercial wrist and stop watch. Considering the facile fabrication and easily available sustainable materials used for the aPL-TENG, the presented approach can provide attractive green energy harvesting machine to power portable devices at a large scale – without having to worry about the end-of-life electronic waste management

A Wide Range Self-Powered Flexible Pressure Sensor Based on Triboelectric Nanogenerator

This work presents a triboelectric nanogenerators (TENG) based wide-range, self-powered flexible pressure sensor. The fabricated TENG can detect wide range of applied pressure from 3.2 to 1176 kPa. By analyzing the open-circuit voltage versus pressure curve, the sensitivity in three pressure regimes, namely low (1-10 kPa), medium-high (10-500 kPa) and ultra-high (&gt;500 kPa) is extracted. The obtained sensitivities for these three pressure regimes are 3.16, 0.023 and 0.031 V•kPa -1 , respectively. The origin of such a stable response of TENG at all of 3 pressure regimes lies in the use of real contact area of the interface pair. To the best of our knowledge, this is the first time a TENG as self-powered pressure sensor has been characterized over such a wide pressure range covering both low and super high pressures. These results show the potential of TENGs for a wide range of applications such as detecting the pressure in wearables, self-powered e-Skin for sole of humanoid robot to help them walk and stand, and the impact of wave energy

Textile Triboelectric Nanogenerators as Self Powered Wearable Temperature Sensors

Efficient harvesting of ubiquitous ambient mechanical energy such as body movements, vibrations etc. using nanogenerators (NGs) have attracted considerable interest for the development of energy autonomous electronics. Herein, we present a high-performance textile triboelectric nanogenerators (T-TENGs) in fiber form factor using a Polytetrafluoroethylene (PTFE) film in contact with a Nylon based counter-surface in either nanofiber mat or fabric form (both fixed to conductive fabric electrodes). T-TENG performance is enhanced by performing Argon plasma treatment on the PTFE film. The plasma treated devices show increase in output voltage by a factor of 7.6, while short circuit current increased by a factor of 11.6 (compared to pristine non-plasma treated devices). We also show that the fabricated T-TENG can be used as a self-powered temperature sensor within the 25-90°C range. TENG voltage decreased linearly with increasing temperature exhibiting a sensitivity of -0.85/°C. To the best of our knowledge, this is the first demonstration of a T-TENG based self-powered temperature sensor. These results show the potential of T-TENGs for several applications such as detecting temperature in the human body and in self-powered e-Skin for the gloves of humanoid robots etc

Integrated piezo-triboelectric nanogenerators based self-powered flexible temperature and pressure sensor

No abstract available

Origin of the contact force-dependent response of triboelectric nanogenerators

Triboelectric nanogenerators (TENGs) have attracted significant interest as the alternative source of renewable energy. Their performance is believed to depend on the contact force, but its origin is yet to be established. Herein, we show that the origin lies in the real contact area Ar, probed with novel experiments specifically designed for this purpose. The open circuit voltage Voc, short circuit current I8c and Ar for a TENG, having two nominally flat tribo-contact surfaces, were found to increase with contact force/pressure. The Ar is notably small at low pressures (0.25% at 16 kPa) that are typically experienced in wearable applications. However, it increases 328 fold to as much as 82% when it saturates beyond about 1.12 MPa pressure - achievable for impact with ocean waves. Critically, Voc and I8c saturate at the same contact pressure as Ar suggesting that electrical output follows the evolution of the Ar. Assuming that tribo-charges can only transfer across the interface at areas of real contact, it follows that an increasing Ar with contact pressure should produce a corresponding increase in the electrical output. These results underline the importance of accounting for real contact area in TENG design to boost their performance, the distinction between real and nominal contact area in tribo-charge density definition, and the possibility of using TENGs as a self-powered pressure/load sensors. Crucially, the results indicate that the large contact pressures, readily available in applications such as road-tyre contact and wave energy, alone could be enough to boost the performance, thus avoiding the need for costly surface engineering to increase Ar

Identification of DNA methylation prognostic signature of acute myelocytic leukemia.

BACKGROUND:The aim of this study is to find the potential survival related DNA methylation signature capable of predicting survival time for acute myelocytic leukemia (AML) patients. METHODS:DNA methylation data were downloaded. DNA methylation signature was identified in the training group, and subsequently validated in an independent validation group. The overall survival of DNA methylation signature was performed. Functional analysis was used to explore the function of corresponding genes of DNA methylation signature. Differentially methylated sites and CpG islands were also identified in poor-risk group. RESULTS:A DNA methylation signature involving 8 DNA methylation sites and 6 genes were identified. Functional analysis showed that protein binding and cytoplasm were the only two enriched Gene Ontology terms. A total of 70 differentially methylated sites and 6 differentially methylated CpG islands were identified in poor-risk group. CONCLUSIONS:The identified survival related DNA methylation signature adds to the prognostic value of AML