Electron trapping & blocking effect enabled by MXene/TiO₂ intermediate layer for charge regulation of triboelectric nanogenerators

As the existence of interfacial electric field, the surface charges of triboelectric nanogenerators (TENGs) would diffuse into air or tribo-material interior, resulting in the charge decay. Therefore, charge regulation from charge storage is crucial in addition to charge generation. In this work, a MXene/TiO₂ hybrid film has been prepared through partial oxidation of MXene in a contact-separate mode TENG (MT-TENG) as an intermediate layer between negative tribo-material and bottom electrode. It demonstrates the electric outputs of 128 μC/m² in charge density, 73.78 μW/cm³ and 63.78 μW/g in average power density with an energy conversion efficiency of 34.81%. The surface terminals in MXene nanosheets and the oxygen vacancies in TiO₂ nanoparticles provide abundant electron trap sites. Moreover, the energy band bending resulting from the polarization effect of the hybrid film could further hinder the free electrons' drift to the bottom electrode, and consequently prevent the charge recombination. With the synergetic effect of electron storage and polarization, the MT-TENG with an intermediate layer rapidly reaches a charge dynamic equilibrium with a charge density of 80 μC/m². It is expected to provide new insights for material science and structure design from the perspective of charge regulation to improve the output performance of TENGs.