3D‐Printed Double Piezoelectric NaNbO ₃ @PVDF‐HFP Composite‐Based Waterproof Triboelectric Nanogenerator for Enhanced Energy Harvesting and Intelligent Array‐Type Touchpad Control

ABSTRACT This work reports the fabrication of a 3D‐printed double piezoelectric layer‐supported flexible and waterproof triboelectric nanogenerator (3D‐NPTENG) for enhanced energy harvesting and a self‐powered array‐based HMI application. The device consists of 3D‐printed NaNbO ₃ @PVDF‐HFP double piezoelectric composites with an interspaced electrode as piezoelectric material, an ecoflex layer as tribo‐negative material, and copper electrodes. 3D‐printing method delivers a poling‐free process, offering a scalable and cost‐effective fabrication technique. The interspaced electrode accelerates the generation of the piezoelectric charges, offering 2.82 times higher piezoelectric coefficient (d ₃₃ = 255.4 ± 10 pC/N) compared to the single‐layer configuration. Under the finger tapping (13.2 N), the 3D‐NPTENG generates 228 V output voltage and 1.5 W/m ² power density and also delivers a fast response time(7 ms) with sensitivity of 13.7 ± 3.4 V/kPa in the region from 0.2 to 0.8 kPa pressure. By charging 2.2 and 10 µF capacitors and illuminating 38 LEDs, the device confirms its excellent energy conversion ability. Moreover, it exhibits long‐term durability and water‐resistant properties, maintaining stable performance over 7000 cycles under continuous mechanical force, applied by customized sewing‐machine. Furthermore, the device is utilized to develop an auto‐powered array‐based touchpad capable of controlling multiple functions, demonstrating a new pathway in terrestrial and underwater HMI.