Electrospinning Equipment: High-Performance Coupled Nanogenerators from Electrospun Porous PU@PVDF-ZnO Nanofibers

In the era of the Internet of Things, electronic devices are becoming increasingly miniaturized and portable. Traditional energy technologies struggle to meet their energy demands. The micro-nano energy field has emerged. By leveraging cutting-edge micro-nano materials and technologies, micro-nano energy can effectively harvest and store ambient energy, providing continuous, maintenance-free, and self-sustaining power for electronic devices. Among them, coupled nanogenerators, which combine the triboelectric and piezoelectric effects, have significant advantages. However, current methods for enhancing their performance suffer from high costs and complex processes, urgently needing to be addressed.  

Recently, a research team led by Professor Zhou Chen from the College of Mechanical and Power Engineering at Nanjing Tech University published the latest research results titled "High-Performance Coupled Nanogenerators Based on Electrospun Porous PU@PVDF-ZnO Nanofibers with Core–Shell Structure" in the journal Advanced Engineering Materials. The team prepared a high-performance coupled nanogenerator based on porous core-shell structured nanofibers through the electrospinning machine technique. This achievement provides new material design ideas for the field of sustainable energy harvesting and is expected to promote the development of wearable electronic devices.

The team combined materials through the electrospinning device and successfully prepared four different types of nanofibers, including PVDF-ZnO nanofibers, porous PVDF nanofibers, PU@PVDF nanofibers, and porous PU@PVDF-ZnO nanofibers. The preparation process of these fibers involves the preparation of various mixing solutions, magnetic stirring to achieve a homogeneous composite, and electrospinning under a high electric field (see Figure 1 for details).

Figure 1. Preparation of nanofibers and coupled nanogenerator: A) preparation process of PVDF-ZnO, porous PVDF, PU@PVDF, and PU@PVDF/PVP-ZnO nanofibers and B) the coupled nanogenerator structure

Among them, the porous PU@PVDF-ZnO nanofibers are further treated with ultrasonic oscillation in ethanol and deionized water after preparation to remove polyvinylpyrrolidone (PVP), forming a porous structure. This step significantly increases the surface roughness and specific surface area of the fibers (see Figure 2a - e). The research also focused on the impact of different ZnO concentrations on the fiber properties and found that the addition of ZnO promoted the formation of the β-phase in PVDF.

Figure 2. FE-SEM image and diameter distribution histogram of nanofibers: A–E) histogram of diameter distribution of PVDF-ZnO, porous PVDF, PU@PVDF, PU@PVDF/PVP-ZnO, and porous PU@PVDF-ZnO fibers, F) water contact angle of PU@PVDF/PVP-ZnO fiber membrane, and G) water contact angle of porous PU@PVDF-ZnO fiber membrane

The nanogenerator based on porous PU@PVDF-ZnO fibers exhibits excellent electrical properties. Experimental data show that the output voltage of this nanogenerator can reach 129.3 V, the short-circuit current is 0.644 μA, and the output power density is 0.0021 μW/m². These performance indicators indicate significant advantages of the device in energy harvesting and conversion (see Figure 3a, b).

Figure 3. A,B) Output performance of coupled PVDF-ZnO nanogenerator with different ZnO content, C) operating principle of coupled nanogenerator, D) TEM image of PVDF-ZnO, E) TEM image of PU@PVDF, and F) TEM image of porous PU@PVDFZnO

In addition to electrical properties, the nanogenerator also shows excellent mechanical properties. Its tensile strength reaches 8.8 MPa, and the elongation at break is 196.7% (see Figure 4). Moreover, the nanofiber membrane has a water contact angle of 104.75°, indicating good hydrophobicity. In a high-temperature environment of 160 °C, the fiber membrane can still maintain good morphological integrity. In the durability test, after 5000 cycles of contact separation, its electrical output remains stable, demonstrating the reliability of the device during long-term use (see Figure 5i).

Figure 4. Thickness distribution and stress-strain curves of nanofiber membranes: A) PVDF-ZnO, B) porous PVDF, C) PU@PVDF, D) PU@PVDF/PVP-ZnO, E) porous PU@PVDF-ZnO, and F–H) stress–strain curves

In practical application tests, the nanogenerator shows potential in human motion detection and powering small devices. In the experiment, by simulating the clapping action, the device successfully lit five LED bulbs, proving its ability to convert mechanical energy into electrical energy and power devices (see Figure 5k, l, m). In addition, the nanogenerator based on the porous PU@PVDF-ZnO fiber membrane not only has excellent performance but also good flexibility and washability. In the experiment, the fiber membrane was immersed in water and magnetically stirred to simulate the washing process. After 24 hours, the output voltage and current of the dried and reassembled nanogenerator were basically the same as those before washing, remaining at approximately 130 V and 0.6 μA, respectively, indicating its durability and stability in practical applications. This makes the nanogenerator have great application potential in the field of wearable electronic devices (see Figure 5g, h).

Figure 5. A,B) Output performance of coupled nanogenerator at different frequencies, C) output performance of coupled nanogenerator at different contact areas, D,E) output performance of coupled nanogenerator at different separation distances, F) comparison of the performance of coupled nanogenerator and piezoelectric nanogenerator based on porous PU@PVDF-ZnO nanofiber, G,H) performance comparison of nanofiber membrane before and after washing, I) cycling stability of nanogenerator, J) circuit management system, K,L) driving nanogenerator by clapping, and M) lighted LEDs

Article source: https://doi.org/10.1002/adem.202500549