Ferromagnetic nanoparticle-embedded hybrid nanogenerator for harvesting omnidirectional vibration energy

A new form of generator known as the triboelectric nanogenerator (TENG) has recently been suggested as a simple and low-cost solution to scavenge ambient mechanical energy. Although there have been substantial advances in TENGs over the past few years, the power efficiency of TENGs must be enhanced further before they can be practically applied. In the present study, we report a ferromagnetic nanoparticle-embedded hybrid nanogenerator (FHNG) which operates based on both triboelectricity and electromagnetic induction. A TENG and an electromagnetic generator (EMG) efficiently cooperate to generate electrical energy from the same motion, i.e., the vibration of a synthesized nanoparticle. A surface-functionalized ferric oxide nanoparticle, which has strong ferromagnetism and high triboelectricity, was produced by a simple surface-coating process. The measured electrical characteristics revealed that the output voltage of both the TENG and the EMG components increased by approximately 50 times and by twofold, respectively, after the surface functionalization step. Moreover, when constant vibration of 3 Hz is applied to the fabricated FHNG, the TENG and EMG components correspondingly generated output power of 133.2 μW at a load resistance of 100 MΩ and 6.5 μW at a load resistance of 200 Ω. The output power per unit mass from the FHNG is greater than that according to the arithmetic sum of the individual TENG and EMG components, demonstrating synergy between the two components. Furthermore, the device can generate stable output under various vibration directions, amplitudes, and frequencies due to the fluid-like characteristics of the powder. The packaged structure also securely protects the device from external humidity and dust. Connected to a rationally designed power management circuit, a digital clock was turned on solely by the fabricated FHNG.