Soft-contact cylindrical triboelectric-electromagnetic hybrid nanogenerator based on swing structure for ultra-low frequency water wave energy harvesting

Ocean waves are promising green sources for energy exploitation, but harvesting such energy is quite challenging due to the apparent drawbacks of ultra-low vibration frequency and low efficiency. Here, a hybrid nanogenerator containing soft-contact cylindrical triboelectric nanogenerator and electromagnetic generator with swing structure was designed for ultra-low frequency wave energy converting. Brushes made of flexible rabbit hairs were introduced to separate stator-rotor pairs, with the function of charge pumping onto dielectric surface, which can reduce the operation resistance and improve the device durability. Based on the swing motion of rotor, over 60 current pulses can be generated within 15 s from either module by one external triggering, implying the output frequency multiplication and operation time extension. The optimized hybrid nanogenerator exhibits the best output response at 0.1 Hz of water wave agitation, delivering a peak power density of 10.16 W·m−3 and an average power density of 0.23 W·m−3. Furthermore, self-powered temperature mapping and wireless transmitting were successfully realized by a hybrid nanogenerator array to demonstrate its capability in collecting ultra-low frequency water wave energy. The distinctive structure and operation mechanism prompt the proposed hybrid nanogenerator to be a good candidate for large-scale blue energy harvesting.