Stretchable polyurethane composite foam triboelectric nanogenerator with tunable microwave absorption properties at elevated temperature

Highlights: • A high-performance composite foam-based triboelectric nanogenerator with microwave absorbing capability is presented. • Tadpole-like CNTs@Fe₃O₄ nanoparticles are successfully synthesized as microwave absorbing units and conductive fillers. • The CNTs@Fe₃O₄/PU CF-TENG could generate a maximum output power of 147.9 μW and easily illuminate 35 commercial LEDs. • An outstanding MA performance with an RL_m value of −68.5 dB and an ultrabroad EAB of 4.37 GHz at a thickness of 2.55 mm. • The CF-TENG can be repeatedly folded, compressed, stretched and possessed thermally tunable ability of MA capacity. Nowadays, the integration of multiple functions such as harvesting clean energy and electromagnetic protection into single material has attracted great interest. Herein, a stretchable composite foam-based triboelectric nanogenerator (CF-TENG) with tunable microwave absorption (MA) capacity was developed by assembling self-foaming polyurethane (PU), tadpole-like CNTs@Fe₃O₄ nanoparticles (NPs) and conductive wires. The CF-TENG with a volume of ∅120 mm × 3 mm can generate a maximum output power of 147.9 μW, corresponding to a power density of 1.3 µW/cm² and easily illuminate 35 commercial light-emitting diodes (LEDs) under periodically vertical contact and separation mode, which exhibits high efficiency in energy-harvesting. Besides, the excellent MA properties and relevant mechanisms at elevated temperatures from 253 K to 333 K were investigated in detail. With an ultralow filler loading of 15 wt%, the minimum reflection loss (RL_m) value at 253 K could reach −68.5 dB at 10.97 GHz and effective absorption bandwidth (EAB) below −10 dB achieved 4.37 GHz at a thickness of 2.55 mm. Temperature rise would be conducive to broadening the EAB and shifting the matching frequency towards a higher frequency band. Such a remarkable MA performance originated mainly from the dielectric-magnetic dual loss, well-matched impedance, and multiple reflections. To this end, this CF-TENG with electromagnetic protection property combining the ability to scavenge mechanical energy from ambient vibrations opens a new set of prospective applications in wearable electronics and the next-generation energy systems under invisible harsh environments.