High-Performance Dual-Mode Triboelectric Nanogenerator Based on Fe3O4/PDMS Composite and LIG Electrodes for Wave Energy Harvesting

Abstract Harvesting marine wave energy using triboelectric nanogenerators (TENGs) offers a promising route toward sustainable blue energy, yet most existing designs suffer from limited output under low-frequency and random wave excitation. Unlike previous dual-mode TENGs based on separately assembled units or external switching, this work integrates contact-separation (CS) and freestanding-layer (FL) modes in a single swing lever, both using the same Fe3O4/PDMS composite tribo-layer and LIG electrodes, with the Fe3O4 content (0–8%) tuned to optimize each mode independently. Optimal concentrations are 6% for the CS-TENG and 4% for the FL-TENG, balancing dielectric enhancement against agglomeration-induced charge leakage. Under identical swing excitation, the dual-mode TENG (DM-TENG) delivers an open-circuit voltage of 82 V, a short-circuit current of 37.9 μA, and a transferred charge of 51.7 nC, achieving a peak power of 640 μW at 10 MΩ and a power density of 266.7 mW/m2. Compared to the CS-TENG and FL-TENG operating independently, the dual-mode configuration improves voltage by factors of approximately 2 and 14, current by 1.26 and 18, and charge by 1.75 and 6.6, respectively. The short-circuit current increases continuously with excitation frequency from 0.2 to 2 Hz, covering the typical frequency range of ocean waves. The DM-TENG successfully charges various capacitors within 100 s and powers a commercial hygrometer/thermometer in a water tank with a sealed acrylic box, confirming its ability to harvest wave energy and store it in capacitors for driving low-power electronic devices.