Enhanced thermoelectric performance of graphene based nanocomposite coated self-powered wearable e-textiles for energy harvesting from human body heat

Abstract

The demand for highly flexible and self-powered wearable textile devices has increased in recent years. Graphene coated textile-based wearable devices have been used for energy harvesting and storage due to their outstanding mechanical, electrical and electronic properties. However, the use of metal based nanocomposites is limited in textiles, due to their poor bending, fixation, and binding on textiles. We present here reduced graphene oxide (rGO) as an n-type and conductive polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) as a p-type material for a wearable thermoelectric nanogenerator (TEG) using a (pad-dry-cure) technique. We developed a reduced graphene oxide (rGO) coated textile-based wearable TEG for energy harvesting from low-grade human body heat. The conductive polymer (PEDOT:PSS) and (rGO) nanocomposite were coated using a layer by layer approach. The resultant fabric showed higher weight pickup of 60-80%. The developed textile based TEG device showed an enhanced Seebeck coefficient of (25-150 μV K^-1), and a power factor of (2.5-60 μW m^-1 K^-1). The developed TE device showed a higher potential to convert the low-grade body heat into electrical energy, between the human body temperature of (36.5 °C) and an external environment of (20.0 ± 5 °C) with a temperature difference of (2.5-16.5 °C). The wearable textile-based TEG is capable of producing an open circuit output voltage of 12.5-119.5 mV at an ambient fixed temperature of (20 °C). The rGO coated textile fabric also showed reduced electrical sheet resistance by increasing the number of dyeing cycles (10) and increased with the number of (20) washing cycles. The developed reduced graphene oxide (rGO) coated electrodes showed a sheet resistance of 185-45 kΩ and (15 kΩ) for PEDOT:PSS-rGO nanocomposites respectively. Furthermore, the mechanical performance of the as coated textile fabric was enhanced from (20-80 mPa) with increasing number of padding cycles. The thermoelectric performance was significantly improved, without influencing the breath-ability and comfort properties of the resultant fabric. This study presents a promising approach for the fabrication of PEDOT:PSS/rGO nano-hybrids for textile-based wearable thermoelectric generators (TEGs) for energy harvesting from low-grade body heat.

Fig. 1. Fabrication of conductive textiles (a) GO coating on padder machine, fabric GO and rGO coated fabric strips compared to pristine fabric (b) sheet resistance of rGO coated fabric with different cord length (cm) connected with LED light (c) stretching and bending of TE generator connected with 2-probe digital voltmeter for sheet resistance (d) TE nanogenerator attached to human wrist (e) Seebeck measurement setup with controlled thermal gradient (f) output open circuit (mV) obtained from TENG using Keysight digital and analog voltmeter.

Fig. 2. Effect of rGO content percent 2.5, 5.0, 10.0 and 20.0 on weight pickup percentage of textile substrate coated with GO, rGO and PEDOT:PSS-rGO.

Fig. 3. Weight pick up% and particle size distribution of GO, rGO and PEDOT:PSS-rGO nano composite.

Fig. 4. Effect of different weight percent of GO, rGO and PEDOT:PSS-rGO nano composite on water contact angle.

Fig. 5. Effect of different weight percent of GO, rGO and PEDOT:PSS on tensile strength of the coated fabric.

Fig. 6. Effect of different weight percent of GO, rGO and PEDOT:PSS on electrical sheet resistance of as coated fabric.

Fig. 7. Effect of washing cycles on electrical sheet resistance of as coated textile substrate with different weight percent of rGO and PEDOT:PSS-rGO nano composite.

Fig. 8. Effect of temperature gradient on thermoelectric performance of as coated substrate with different weight percent of rGO and PEDOT:PSS nano composite.

Fig. 9. Effect of temperature and different weight percent of rGO on thermoelectric performance power factor of textile substrate.

Fig. 10. Effect of temperature gradient on output electric potential (mV) as coated textile based TE device with different weight percent of rGO and PEDOT:PSS-rGO nano composite.

Fig. 11. Overall thermoelectric TE performance of textile based device, (a) output electric potential (mV) (b) current (mA) (c) voltage vs. current and power density (d) output electric potential and power of TE device with variable TE legs.