Functionalized Cu-Doped ZnO/PVDF Composite: An Excellent Energy Storage Material for Wearable Devices

Human health and well-being are major focuses of current research worldwide. Self-powered smart wearable technology holds great promise for enhancing human life. However, developing materials with a high energy storage capacity for powering sensors, wearables, and portable electronics remains challenging. Here, we report on the design of a composite material, PVDF/f-Zn_1–xCu_xO (x = 0, 0.01, 0.02, 0.03), with high energy storage and energy- harvesting capacity. The material was synthesized via a hydrothermal process, in which copper (Cu) was doped into zinc oxide (ZnO) and then amine-functionalized with 3-aminopropyl triethoxysilane (APTES). Interestingly, the 2 wt % Cu-doped ZnO transformed from a nanoflake to a uniaxial nanorod morphology during synthesis, a key factor for high-energy storage properties. The modification of APTES facilitated the dispersion of uniaxial fillers within the polymer matrix. Adding f-Zn_0.98Cu_0.02O to polyvinylidene fluoride (PVDF) resulted in a 154% increase in tensile strength and a 56% increase in Young’s modulus compared with neat PVDF. Moreover, the PVDF/f-Zn_0.98Cu_0.02O nanocomposite exhibited excellent energy storage density (9 J/cm³) and efficiency (81%). Additionally, it demonstrated an impressive piezoresponse, with an output voltage of ∼12 V and a power density of approximately 21.17 μW/cm², significantly higher than those of neat PVDF and other contemporary composites. The efficiency of the composite for wearable devices was tested through various biomechanical pressure applications such as finger tapping, hand stomping, and finger bending, and it showed outstanding responses.