Significant triboelectric enhancement using interfacial piezoelectric ZnO nanosheet layer

TLDR: In this article, a triboelectric nanogenerators (TENG) based on phase inversion membranes of polyvinylidene fluoride (PVDF) and polyamide-6 (PA6) were used to achieve a significant enhancement in the power density.

About: This article is published in Nano Energy.The article was published on 2017-10-01 and is currently open access. It has received 36 citations till now. The article focuses on the topics: Nanogenerator & Piezoelectric coefficient.

Figures

Fig. 6. (a) The stability test of TENG sample S4 carried out for 9000 cycles at a force of 30 N at a driving frequency of 5 Hz, (b) lighting a group of 35 red LED’s with as fabricated TENG device by charging a 1 たF capacitor.

Fig. 8: (a) PFM amplitude image and (b) PFM phase for S1, (c) and (d) for S2, (e) and (f) for S4 devices, respectively. White dot highlighted areas in (f) show preferential growth of polarisation.

Table 1: Summary of sturtcutres of the fabricated TENG devices.

Fig. 2. SEM top view image (a) and cross-sectional view image (b) for the pristine ZnO nanosheets n Al substrate, (c) and (d) for PVDF membrane on ZnO/Al, (e) and (f) for ZnSnO3/PVDF membrane on ZnO/Al device, respectively. The insets in (a), (c) and (e) are the EDS measurement results for the corresponding samples.

Fig. 4. (a) Open circuit voltage (Voc) and (b) short circuit current densities (JSC) of sample S1, corresponding Voc and Jsc values (c) and (d) for sample S2, while (e) and (f) show the Voc and Jsc values for sample S4. The effect of an interfacial ZnO nanosheet layer is best illustrated in the variation of (g) Voc and (h) Jsc values for samples S3 and S4. All measurements were carried out at a constant force of 50 N and spacer distance of 8 mm.

Frequently asked questions

Q1. What are the contributions in "Significant triboelectric enhancement using interfacial piezoelectric zno nanosheet layer" ?

Utilising an interfacial piezoelectric ZnO nanosheet layer, a significant enhancement in the power density is reported for the triboelectric nanogenerators ( TENG ) based on phase inversion membranes of polyvinylidene fluoride ( PVDF ) and polyamide-6 ( PA6 ). The enhancement in the surface charge density provided by the interfacial piezoelectric ZnO layer is also reflected in the high piezoelectric coefficient d33 ( -74 pmV ) as compared to the pristine fluoropolymer membranes ( -50 pmV ). Under compressive stress, the piezoelectric potential thus produced in the ZnO nanosheets provides charge injection on to the surface of ZnSnO3-PVDF membrane, improving the charge density, which in-turn significantly enhances the power density from 0. 11 to ~1. 8 W/m. For tribo-negative membranes incorporating the interfacial ZnO layer, piezoelectric force microscopy measurements further show enhanced domain size which can be attributed to the interfacial dipole-dipole interaction with the ferroelectric polarization of PVDF, which promotes the alignment with the polar axis of ZnO. 

Q2. What happens when the structure is released?

When the applied force is released, the structure starts to bounce back, leading to the movement/flow of charges through the external circuit. 

Q3. What is the effect of the electric field on the -crystals?

As water is a dipolar molecule, the electric field acts on the initial surface, inducing aligned く-crystals, which in turn causes the alignment of the く-phase crystals in the sequential crystallisation. 

Q4. What is the effect of the thermal field gradient on the ZnO nanosheet?

When the spin coated PVDF, ZnSnO3-PVDF dope solution deposited on the ZnO nanosheet layer undergoes fast quenching at low temperature, a strong thermal field gradient is induced, which can also cause the crystals to align along the thermal field direction [22]. 

Q5. Why are the ZnO nanosheets more stable under the large external loads?

due to morphologically inter-connected structure, as compared to the ZnO nanorods, the two-dimensional (2D) ZnO nanosheet structures are mechanically more stable under the large external mechanical loads [31]. 

Q6. What is the effect of the contact force on the output of TENGs?

For the pristine PVDF/ZnO/Al system, the contact force still has a significant effect on the output performance of TENGs which is believed to arise from the elastic nature of the contacting materials, with a larger contact force substantially modifying the effective contact/charging area [21, 27, 28]. 

Q7. What is the effect of the piezoelectric ZnO nanosheets on the output?

On their own, the ZnO/Al system is only able to provide a small voltage and current output of ~20 V and ~1 mA/m2, respectively; however, working synergistically with the ZnSnO3-PVDF composite film, the huge increase in output performance for S4 is considered to be caused mainly by the polarisation induced charges by the piezoelectric ZnO nanosheets. 

Q8. What is the way to measure the piezoelectric response of ZnO nanosheet?

When an Al substrate is used, ZnO nanosheets are typically observed, which are particularly useful for the application in TENGs as the structure provides large surface areas for charge generation. 

Q9. What is the effect of the interfacial ZnO nanosheet on the output voltage?

In the triboelectric configuration i.e. with a spacer, the high-density ZnO nanosheet structure should ideally provide substantially large effective contact area due to the nanostructures. 

Q10. How much does the output voltage and current density increase for the PA6/PVDF T?

The output voltage and current density typically increase by 2.5 times for the PA6/(ZnSnO3PVDF) TENG as compared to PA6/PVDF without ZnSnO3 nanomaterial [16]. 

Q11. What is the effect of phase inversion on the ZnO nanosheets?

It is evident from the SEM images that the respective dope solutions penetrate deep into the ZnO nanosheet architecture, and upon crystallisation during phase inversion process fill up the gaps in the structure to form uniform membranes. 

Q12. What is the effect of ZnO nanosheets on the electrical output of the TENG?

When the applied force is raised further, the introduction of stress onto the ZnSnO3 nanocubes and indeed the ZnO nanosheets leads to the creation of a strong and cumulative piezoelectric potential. 

Q13. What was the spacing between the top and bottom of the TENG?

Two arc-shaped polyimide sheets were used to maintain the desired spacing between the top and bottom parts of the TENG, as shown in Fig. 

Q14. What is the underlying mechanism of the observed increase in the crystallinity and phase content?

The observed increase in the crystallinity and the くphase content upon the addition of ZnSnO3 is consistent with their previous work and arises due to the interfacial interactions between PVDF and ZnSnO3 nanomaterial [16]. 

Q15. What is the effect of interfacial ZnO nanosheets on the output performance?

In fact, all the electrical characterisation data indicates that the incorporation of interfacial ZnO nanosheet layer has a more profound effect on the output performance of the TENGs, possibly through polarisation induced charges [10, 32, 33].