Wearable ionogel fiber-based ionic thermoelectric device for low-grade human body heat harvesting

Wearable fiber-based thermoelectric generators (TEGs) with high thermoelectric (TE) performance, mechanical property and wearing comfort are urgently needed for low-grade human body heat harvesting. To get a high thermovoltage, a wearable ionogel fiber-based ionic thermoelectric device is designed and prepared in this study. To synergistically enhance the ionic conductivity and ionic Seebeck coefficient, ethanol and sodium bis(trifluoromethylsulfonyl)imide (NaTFSI) are added into the poly (vinylidene fluoride-co-hexafluoropropylene)/1-ethyl-3-methylimidazolium dicyanamide (PVDF-HFP/EMIM:DCA, PH/ED) ionogel to improve the ionic mobility and enhance the diffusion difference between cations and anions. The morphology, structure, transmittance, crystallization, rheological property, mechanical and thermoelectric performances are analyzed, and then a mechanism for the performance enhancement is proposed. After the modification, high ionic conductivity, ionic Seebeck coefficient and ionic power factor of 17.5 mS/cm, 22.9 mV/K, 870.26 µW/mK2 are obtained for the PH/ED-ethanol-NaTFSI (PH/ED-E-NaTFSI) ionogel at RH 70 %, much higher than those of the pristine PH/ED ionogel. Meanwhile, the tensile stress of the ionogel fiber is significantly enhanced to 18.15 MPa from 0.19 MPa of PH/ED-E-NaTFSI ionogel film. Then, a wearable ionogel fiber-based wristband with synergistically improved TE performance, mechanical property and wearing comfort is prepared by a weaving process. When wearing the i-TE wristband (5-legs) at room temperature (ΔT = 2.7 K), an obviously high thermovoltage of 119.133 mV is generated, indicating its great potential as wearable energy supply devices.