Triboelectrification: From the Principle of Polarization to Application in Energy Harvesting

Abstract

Triboelectric nanogenerators (TENGs) have emerged as promising technologies for energy harvesting and sensing due to their high energy conversion efficiency, lightweight and flexible design, and ability to operate without external power sources. They can effectively convert mechanical energy from motion, vibration, and environmental forces into electrical energy, making them suitable for wearable electronics, biomedical applications, and IoT devices. Additionally, TENGs serve as highly sensitive sensors for detecting pressure, motion, and environmental changes. However, challenges remain in their practical implementation, including low and inconsistent power output, charge dissipation, material wear, and environmental sensitivity. Furthermore, scalability and efficient energy storage integration are critical hurdles that need to be addressed. The lack of standardization in triboelectric charge transfer mechanisms also limits optimization efforts. Despite these challenges, advancements in materials science, device engineering, and power management strategies continue to improve TENG performance, paving the way for their widespread adoption in sustainable energy and sensing applications. This project mainly focused on these critical problems, where strategies were developed to reveal the mechanisms of TENG and elaborate a new perspective on dielectric polarization.

Dielectric polarization plays a fundamental role in various physical and industrial processes, influencing triboelectrification, electrostatic induction, and charge accumulation. However, a universal and quantitative method for assessing dielectric polarization has been lacking. In this first work, a dielectric-adjustable nanogenerator (DANG) composed of Ecoflex silicone and lead zirconate titanate (PZT) composite films were introduced to investigate the relationship between dielectric properties, electrical output, and surface charge behavior. Utilizing piezoelectric force microscopy (PFM) and Kelvin probe force microscopy (KPFM), the study confirmed the occurrence of self-polarization and polarization reversal under a DC bias ranging from -12 V to 12 V, demonstrating their role in enhancing surface charge retention and device performance. The results indicated that dielectric polarization accelerates charge accumulation while prolonging charge decay, directly impacting electrical output. Furthermore, the proposed method was extended to other dielectric materials, establishing a universal framework for quantifying dielectric polarization through surface charge dynamics. This research provides a novel approach for evaluating dielectric properties with broad applications in energy harvesting and electrostatic control.

Despite that TENG has great potential in harvesting high-entropy energy (HEE) from irregular and low-frequency mechanical sources such as wind and water flow, their practical application is hindered by low current output and high impedance. In the following work, a high-entropy energy harvester (HEEH) that integrates charge-trapping (CT) and short-circuit (SC) effects to enhance charge accumulation was introduced, which prevented charge dissipation, and increased charge transfer efficiency. The developed rotary-structured device achieves a record-high volumetric power density of 384 W/m³/Hz, with an 8.5-fold increase in power density and a 7-fold reduction in impedance (from 91 MΩ to 13 MΩ) compared to conventional designs. A specialized power management circuit was also developed to efficiently store and convert high-frequency AC signals, demonstrating superior capacitors and lithium battery charging performance. The effectiveness of HEEH was validated in real-world scenarios, successfully harvesting wind and water flow energy to power an electrochemical wastewater treatment system, decomposing the MO imitated wastewater successfully in 16 hours. The findings highlight a cost-effective, scalable, and highly efficient strategy for large-scale energy harvesting, marking a significant step toward the practical deployment of TENG-based energy solutions.

After realizing that the SC effect plays a pivotal role in understanding the fundamental mechanisms of triboelectrification and offers critical insights for optimizing TENGs. In the following work, the developed SC effect was thoroughly investigated separately. The SC effect is a structural innovation that can significantly enhance TENG performance and was achieved by bridging conductive tribo-layers or electrodes during operation, triggering additional charge transfer and leading to an increase in power density and reduced impedance. A 2.7-fold larger SC peak due to the SC effect, where the extent of enhancement varies across different materials. A 20% faster capacitor charging speed can be realized with one SC contact, which can be further enhanced by increasing the number of SC contact. A soft-contact SC module, utilizing carbon fiber, further ensured long-term stability (6 min, 300 rpm) while maintaining high output. This strategy is universally applicable across classical TENG modes (e.g., contact-separation, lateral sliding), demonstrating exceptional compatibility and scalability.

In summary, synergizing polarization-driven design with the novel SC effect was pursued during this project. The results underscore the transformative potential of TENGs in sustainable energy and personalized healthcare, bridging fundamental triboelectric mechanisms to practical, scalable solutions. In particular, this study aims to bring triboelectrification-based devices a step closer to real world application by taking cost, simplicity, reproducibility, durability and output into account.

Date of Award	6 Aug 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	Walid DAOUD (Supervisor)