Coupling of Piezoelectric and Triboelectric Effects: from Theoretical Analysis to Experimental Verification

Abstract

process is still unclear and even controversial, [8][9][10] nanogenerators can be made utilizing this effect in conjunction with electrostatic induction. After the fi rst triboelectric nanogenerator (TENG) proposed in 2012, [ 11 ] the peak power density of this kind of nanogenerator increases exponentially from 3.67 mW m −2 to 313 W m −2 within 12 months [ 12 ] thanks to the material selection, [ 13 ] morphology optimization, [ 14 ] structure design, [ 15 ] surface modifi cation, [ 16 ] theoretical guidance, [17][18][19] etc. Besides, TENGs cannot only be used as a power source for driving electronic devices, [ 20 ] promoting electrochemical processes, [ 21 ] solving environmental issues, [ 22 ] but also as a self-powered sensor to detect the change of angle, humidity, ion concentration, etc. [23][24][25] Since both the PENG and TENG have the capability to convert mechanical movement into electricity, the combination of both effects is promising in improving the output performance of nanogenerators. To realize the piezoelectric-triboelectric hybrid nanogenerator (PE-TENG), fl exible piezoelectric materials (e.g., ZnO, PVDF) were usually utilized to form the PENG. Then, a vertical contact-separation mode TENG can be introduced to work together with the PENG thus converting mechanical energy into electricity using both piezoelectric and triboelectric effects. [26][27][28][29][30][31][32][33][34][35] Generally, there are three different structures for the PE-TENG: two-terminal structure in which the piezoelectric material also works as one friction material, [26][27][28] three-terminal structure in which one electrode is shared by the PENG and TENG, [29][30][31][32] and four-terminal structure in which the PENG and TENG works independently. [33][34][35] For each structure, the output performance of the hybrid nanogenerator can be modulated (enhanced or reduced) according to the polarity of the piezoelectric material.However, previous investigation of the PE-TENGs mainly focuses on the output improvement, [ 26 ] bandwidth adjustment, [ 33 ] and sensor applications.[ 34 ] The theoretical comparison of piezoelectric and triboelectric effects, the coupling of these two effects at different electrode connections, and the infl uence of electrical parameters, which all have great impact on the output of PE-TENG, have not been discussed before. Therefore, in this work, we fi rst established the theoretical models for the specifi c PENG and TENG with similar structure. On this basis, numerical analysis of PE-TENGs at three different structures and two different operation modes was performed. Further, we investigated the infl uence of piezoelectric polarization Both the piezoelectric and triboelectric effects can be utilized to design and realize high-performance nanogenerators. In addition, the structures of longitudinal piezoelectric nanogenerator (PENG) and single-electrode triboelectric nanogenerator (TENG) show great similarity, which may bring possible combinations of these two types of nanogenerators. Here, the fi rst ...

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