The investigation of energy harvesting from electrospun fibres

Abstract

Wearable technology is a growing and evolving market. Advanced materials that harvest energy can reduce the need for constant device recharging. In this respect, piezoelectric polymers have great potential for use in wearable technology devices and have many advantages compared to traditional ceramic piezoelectric materials. However, the energy harvesting performance of piezoelectric polymers is not as proficient as that of ceramic piezoelectric polymers. Triboelectric and ferroelectret energy harvesters are optional for polymer-based energy harvesting devices with higher efficiency compared to piezoelectric energy harvesters. Triboelectric nanogenerators (TENGs) require materials with a high surface area to improve their efficiency in converting mechanical energy into electrical energy. The increased surface area promotes a greater contact area between the materials, which is essential for maximising charge transfer during the triboelectric effect. This improvement in charge transfer is directly related to the power production and efficiency of the TENGs.

Electrospinning is widely recognised as a highly efficient method for fabricating polymer structures with nanofibrous morphology. This leads to a significant surface area for the confined charge in the electret polymer, which is advantageous for energy harvesting applications. Polyvinylidene Fluoride (PVDF) electrospun fibre is recognised as an excellent performance piezoelectric and triboelectric polymer. The thermal stability of polytetrafluoroethylene (PTFE) ranks among the highest in the negative triboelectric materials series. Polystyrene (PS) increases charge storage in the electret material and exhibits positive surface potential when using the electrospinning technique.

This thesis investigates the development of advanced electrospun fibre structures for energy harvesting applications, focusing on wearable and flexible technology. Energy harvesting devices have gained significant attention as alternatives to conventional batteries, enabling sustainable and lightweight solutions for wearable electronics. The research explores the fabrication and performance evaluation of composite, hollow, and coaxial electrospun fibres, with an emphasis on their triboelectric and ferroelectret properties.

Composite electrospun fibres of PTFE/PVDF were fabricated using a one-step electrospinning technique. The optimised composition demonstrated a substantial enhancement in triboelectric energy harvesting performance, achieving a power density of 348.5 mW/m². Practical applications, such as shoe insoles and book-shaped energy harvesters, showcased the material's potential in wearable technology.

Hollow structure PVDF fibres were produced using a novel one-step coaxial electrospinning method. This design significantly improved piezoelectric properties, achieving a maximum3 power density of 2.18 mW/m² compared to the solid structure of electrospun PVDF. However, the experimental results might be insufficient to indicate the working principle of ferroelectretbased energy harvesters. Coaxial fibres with PS as the core and PVDF as the shell were developed using a single-nozzle technique. This structure exhibited remarkable triboelectric performance, achieving a power density of 6.27 W/m². Practical demonstrations included efficient capacitor charging and the illumination of LEDs, underscoring the feasibility of this approach for scalable energy harvesting systems.

The research contributes to the growing field of energy harvesting by introducing innovative materials and structures, enhancing power densities, and expanding the applicability of electrospun fibres. These findings lay the groundwork for further advancements in sustainable, high-performance energy harvesting technologies for wearable devices.

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Identifiers

ORCID for Pattarinee White: orcid.org/0000-0001-6341-6378

ORCID for Stephen Beeby: orcid.org/0000-0002-0800-1759

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