Materials Beyond Conventional Triboelectric Series for Fabrication and Applications of Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) were first developed in 2012, and have become the desirable choice as energy harvesters in the research community worldwide. The popularity of TENGs is attributed to their low weight, low cost, high output, wide range of materials and device designs. TENGs have been explored for many applications including sensing, implantable power sources, healthcare, and biomedical applications. The performance of TENGs depends largely on the material since charge density (σ) is a material property. Moreover, 2D materials have been investigated as an alternative to the conventional metal electrodes. The dominance of polymers and metals in the traditional triboelectric series has lead researchers to explore novel materials to extend the applications and improve TENG output. This review article summarizes the progress in the development of frictional layers and electrode materials for TENGs. The mechanism for the output enhancement and device applications are discussed in detail. Finally, a perspective on the future and relevant challenges in material development for TENGs are discussed. The development of materials for active triboelectric layers, electrodes, and their applications are systematically reviewed. The review focusses on the materials beyond the conventional triboelectric series, dominated by the polymers and a few metals. This review also outlines the challenges and future perspectives on the development of materials for triboelectric nanogenerators (TENG).