Electrospinning Device for Nanofibers| Confined orientation PVDF/MXene nanofibers forwearable piezoelectric nanogenerators*

The pursuit of high-performance wearable piezoelectric nanogenerators (PENGs) has intensified attention on polyvinylidene fluoride (PVDF). Traditionally, the uneven distribution of the piezoelectrically active β-phase has caused variable material properties and inconsistent device performance, hindering the optimization of piezoelectric responses in nanofibers. 

In response, Professor Weiqing Yang and colleagues at Southwest Jiaotong University proposed a novel confined orientation structure of PVDF/MXene nanofibers, significantly enhancing electromechanical performance without sacrificing flexibility. By incorporating MXene into the PVDF matrix, the formation of the β-phase was successfully induced, achieving a piezoelectric coefficient of 61.7 pC/N. This integration promotes synergistic enhancement of materials and structure, leading to highly oriented and confined MXene nanosheets within the fibers, thereby optimizing force transfer and energy harvesting capabilities. As a result, the nanofiber-based PENG exhibits an excellent response time of 14 ms and a pressure sensitivity as high as 19.29 mV/kPa. The relevant research was published in the journal Journal of Materials Chemistry A under the title "Confined Orientation PVDF/MXene Nanofibers for Wearable Piezoelectric Nanogenerators."

Figure 1. Concept and design of PENGs for martial arts motion monitoring. (a) Schematic of monitoring compression and bending motion signals via PENGs. (b) Digital image and schematic of a wearable PENG array at a joint. (c) Schematic of piezoelectric nanofiber design and structural design. (d) Schematic of oriented and spatially confined structures for enhancing composite piezoelectricity.

• Multifunctionality: Capable of harvesting mechanical energy (e.g., from martial arts movements) and distinguishing different motion types through signal variations.

• Wearable Adaptability: With a breathability rate of 1700 g·m⁻²·d⁻¹, a thickness of only 139 μm, and balanced flexibility and mechanical strength (tensile strength 38.27 MPa), it is suitable for long-term wear.

• Array Scalability: PENG arrays enable visualizing pressure distribution, applicable to scenarios requiring multi-dimensional sensing (e.g., sports biomechanics analysis).

Figure 2. Structural design characterization. (a) SEM images of nanofibers prepared at different rotation speeds. (b) FT images of nanofibers prepared at different rotation speeds derived from (a). (c) Relative angle distribution functions of nanofibers prepared at different rotation speeds derived from (a). (d) Proportion of effectively oriented fibers. (e) 2D-SAXS patterns of nanofibers prepared at different rotation speeds. (f) HD-TEM image of MXene/PVDF nanofibers.

Figure 3. Characterization of MXene/PVDF nanofiber membranes. (a) Digital image showing membrane mechanical compliance. (b) XRD patterns of membranes prepared at different rotation speeds. (c) FTIR spectra of membranes prepared at different rotation speeds. (d) Schematic illustrating the mechanism of membrane anisotropic mechanical properties. (e) Stress-strain curves of membranes prepared at different rotation speeds. (f) Comparison of mechanical properties of membranes prepared at different rotation speeds. (g) Moisture permeability measurements of membranes prepared at different rotation speeds. (h) Piezoelectric coefficients of membranes prepared at different rotation speeds. (i) Comprehensive comparison of membranes prepared at different rotation speeds.

Figure 4. Electrical properties of the PENG based on nanofiber membranes. (a) Exploded view of the fabricated PENG. (b) Digital image of the PENG. (c) Response and recovery times of the PENG. (d-e) Voltage and current outputs of PENGs made from the membrane. (f) Measured outputs of forward and reverse connections for the S-2000 sample. (g) Sensitivity of the PENG. (h) Durability test of the PENG.

Figure 5. Applications in energy harvesting and signal monitoring of various combat movements. (a-c) Schematic diagrams, digital images, and corresponding signals of horizontal kicks, downward kicks, and upward kicks. (d) Schematic of PENG array detecting a box. (e) Voltage signals from the detection box. (f) Current responses of each unit in the PENG array. (g) Schematic and digital image of PENG array detecting forearm blocking an upward kick. (h) Schematic of two piezoelectric response modes in (g). (i) Voltage output in (g).