Charge-trapping-blocking Layer For Enhanced Triboelectric Nanogenerators And Mechanism Studies

In 21st century,the demand for portable and renewable power sources is continuously increasing with the tremendous increase in deployment of wearable electronics.Since 2012,triboelectric nanogenerators(TENG)that are based on the coupling effects of triboelectrification and electrostatic induction have rapidly developed.With many advantages of simple fabrication process,abundant choice of materials,low-cost,light-weight,flexibility,the TENG is considered a promising power choice for wearable electronics in the future.However,the output performance of TENG should be significantly improved as a practical power source.The paramount parameters to determine the electrical output of TENG are the surface triboelectric charges and the electrostatic induced transferred charges between triboelectric layer and electrode.However,on the one hand,the triboelectric charges could decay on the surface of tribo-material,and on the other hand,the diffusion of surface charge into the triboelectric layer and then transferring to the interface between the tribo-layer and electrode could weaken the electrostatic induction effect.Therefore,a multifunctional layered TENG that can reduce the surface charge dissipation and transfer is fabricated,which is the first study focus of this thesis.Clarifying the mechanism of enhancement in output power of the TENG above is the second research focus of this paper.To more efficiently and directly improve the output power of the device by employing charge-blocking layer and conversely validate the mechanism above is the third research focus of this thesis.Based on the above research focuses,this thesis reports the fabrication of wearable TENG to meet the requirement of high output performance by materials synthesis and structural design,and the mechanism of the enhanced effect has also been investigated and elaborated.The main research results are as follows:(1)We present a multifunctional layered TENG(ML-TENG)with an addition of reduced graphene oxide and Ag nanoparticles hybrid layer between a PVDF membrane triboelectric layer and bottom Al electrode to trap and block the interfacial charges,in which the PVDF membrane as the tribo-layer is prepared by the electrospinning process.Subsequently,rGO-AgNPs hybrid layer as the charge-trapping-blocking layer was adhered onto the PVDF membrane closely by the suction filtration process.Furthermore,the rGO solution filtrated at the volume of 10 ml，the concentration of 1.5 mg/ml with AgNPs weight fraction of 70%and the electrospun PVDF solution at the volume of 3 ml were also optimized to yield the best output performance.With the contact area of 22×π cm2,the short-circuit current(Isc),open-circuit voltage(Voc)and transferred charge(Qsc)of ML-TENG can reach 48 μA,335 V and 126 nC,respectively,at 2 Hz.The ML-TENG significantly yielded 100 μC·m-2 in charge density at the optimal condition,which is improved by 8 times compared with that of a pristine TENG with 12 μC·m-2 in charge density.(2)The mechanism of output improvement was investigated.We further clarified the role of rGO-AgNPs hybrid layer as the charge-trapping-blocking-layer by calculating relevant permittivity of tribo-materials,studying the surface potential of tribo-materials and theoretically analyzing electronic energy level.As the results,the surface potentials of the pure PVDF membrane,with the insertion of a rGO film and the modification of AgNPs onto the rGO sheets before the triboelectrification contact are-3.964,-4.611 and-4.807 V,respectively.Correspondingly,the PVDF membrane with a rGO-AgNPs hybrid layer exhibits the largest triboelectric potential difference.Furthermore,the intrinsic structure of rGO and the improved relative permittivity of the tribo-material after the modification of AgNPs on to the rGO sheets proved that the trapping effect of rGO caused by sp2-hybrid structured carbon-atom coupled with the enhanced polarization effect by AgNPs could prevent interfacial charges from diffusing into the air and drifting to the electrode to cancel out the induced positive charges,providing efficient enhancements in TENG output.(3)Furthermore,based on this mechanism,we divided the interlayer into several parts including the charge-trapping layer,charge-blocking layer and charge-transporting layer.More suitable materials were investigated to synthesize the charge-blocking layer to enhance output power.The Qsc of TENG with BaTiO3 doped silicon rubber as charge-blocking layer was 25 nC and further lifted to 41 nC after the TENG was polarized by the polarization instrument,which is improved by 800%compared to that of TENG without charge-blocking layer(5 nC).The mechanism that enhanced polarization of materials can improve the output performance of TENG was further verified.