Recent advances on porous materials and structures for high-performance triboelectric nanogenerators

Since the introduction of triboelectric nanogenerators (TENGs), a variety of dielectric and electrode materials have been developed to improve the TENGs output performance. However, due to their inherent shortcomings, including mechanical deficiencies, insufficient contact area, and limited breathability, the development of TENGs with diverse features and multi functionalities has been limited. To address these challenges, various porous materials and structural designs have been explored in the last decade for development of dielectrics and electrodes. Porous materials include hydrogels, aerogels, foams, and fibrous media, which due to their unique interconnected porous network, high surface area, and tunable pore size distribution, have been shown to be effective in improving the performance and versatility of TENGs. Alternatively, structural designs have also been introduced in the form of textiles and yarns to further expand the functionalities of TENGs. Compared to the first approach, such designs provide larger pores, which can be implemented as air gap in TENG designs. Therefore, these can provide the opportunity for the fabrication of all-in-one TENGs. Given the importance of the above strategies in improving the performance of TENGs and expanding their functionalities, this work aims to summarize, categorize, and highlight the recent advancements in the field of porous materials and structural designs. Representative applications of porous TENGs, including human-machine interfaces, smart wearables, and self-powered sensors with respect to the pore size, are reviewed. The current challenges and future perspectives for integrating porous materials and structures into TENGs are also discussed.