Enhanced performance of an expanded polytetrafluoroethylene-based triboelectric nanogenerator for energy harvesting

Triboelectric nanogenerators (TENGs) are a well-known energy supply technology. Their output performance is highly important given their intended use in real-world applications. Expanded polytetrafluoroethylene (ePTFE) membranes, which are lightweight, fibrillated, microporous membranes formed by the expansion and stretching of PTFE, possess excellent flexibility and elasticity, unlike the traditional PTFE films that they are made from. Therefore, ePTFE membranes have tremendous potential to be a triboelectric material for energy harvesting. As the most important parameter in ePTFE processing, the uniaxial expansion ratio determines the final morphology of the ePTFE and, thus, the output performance of TENGs. Hence, it requires systematic study. Here, folded-paper TENGs consisting of ePTFE membranes with different expansion ratios and nylon fabrics as two paired tribolayers (i.e., ePTFE/Nylon-TENGs) were fabricated. A systematic study concerning the effect of the expansion ratio on the output performance of the ePTFE/Nylon-TENGs was carried out. The output performance of the ePTFE/Nylon TENGs with expansion ratios ranging from 0 to 400% were measured and compared. The results showed that the output electrical signals of the ePTFE/Nylon-TENGs first increased with the expansion ratio and then decreased steadily, with an optimum performance at an expansion ratio of 100%. In addition, the output performance of the TENGs with solid PTFE was approximately the same as that of the ePTFE/Nylon-TENGs with an expansion ratio of 300%. The ePTFE/Nylon-TENGs had excellent and stable performances and yielded a maximum power density of 1.01 mW/cm², with an effective area of 1 cm² and a load resistance of 1 MΩ. This work suggests that ePTFE is an effective material for improving the output performance of ePTFE-based TENGs.