Triboelectric nanogenerators: theoretical calculations, materials, and applications in net-zero emissions

Triboelectric nanogenerators (TENGs) have shown great potential in converting discrete mechanical energy in the environment into electricity without producing any greenhouse gases in the process, and they have been regarded as one of the most powerful methods to achieve zero carbon emissions. It has been confirmed that the output performance is the main factor limiting the real-world applications of the TENGs. Establishing universal standards for quantity analysis TENGs' outputs and seeking advanced dielectric materials to improve the charge density are the two priorities for boosting TENG outputs. Here, the working mechanisms of TENG and the quantitative analysis of TENG output performance are introduced to reveal the relationships of Q-V-I-x (charge-voltage-current-displacement) and the energy conversion efficiencies. Selecting suitable triboelectric materials is the key to enhancing the performance of TENG. Materials used as advanced friction or dielectric layers are elaborated, including metals, inorganic non-metallic materials, polymers, and composites. Moreover, the influences of performance improvement methods, such as ionization injection, intermediate layer, surface modification, and charge-excitation strategy, are discussed accordingly. Finally, applications to achieving the goal of net zero and future challenges of TENGs are presented. This review provides strategies for guiding the further development of TENGs toward higher performances and promoting the commercialization of TENG net-zero systems.