Complementary Electromagnetic–Triboelectric Hybrid Generator for Low-Frequency Energy Harvesting

Ocean waves are abundant but low-frequency (0.1–1 Hz) and irregular; electromagnetic generators (EMGs) deliver high current yet weaken at low velocity, whereas triboelectric nanogenerators (TENGs) sustain high voltage at microampere-level current through megohm-level internal impedance. A sea-state-adaptive hybrid harvester in a compact 3D-printed decagon buoy is proposed, where calm-sea rocking drives a freestanding sliding-mode TENG of polytetrafluoroethylene (PTFE) plates over aluminum electrodes, and rough-sea heave drives the EMG's magnetically levitated NdFeB magnet assembly through copper coils. At 0.5 Hz and ±45°, a single TENG layer with two PTFE plates sliding in the same direction produced a screen-measured ≈15.36 V peak-to-peak open-circuit voltage and 1.25 μW peak power at an optimum load of approximately 5 MΩ. The EMG delivered approximately 1.488 mW under horizontal rocking at a 10 Ω optimum load, near its 16 Ω coil resistance, and charged a 1000 μF capacitor to 2.693 V (≈3.6261 mJ) within 120 s of heave. A preliminary hybrid test, applying both motions simultaneously and combining the separately rectified outputs at the same capacitor, raised stored energy to 5.278 mJ, about 45.56% more than the EMG alone stored, confirming the rectify-then-combine synergy. These complementary electrical and sea-state characteristics support future self-powered marine monitoring buoys.