Abstract
Electrospinning is a simple, versatile technique for fabricating fibrous nanomaterials with the desirable features of extremely high porosities and large surface areas. Using emulsion electrospinning, polytetrafluoroethylene/polyethene oxide (PTFE/PEO) membranes were fabricated followed by a sintering process to obtain pure PTFE fibrous membranes, which were further utilised against a polyamide 6 (PA6) membrane for vertical contact-mode triboelectric nanogenerators (TENGs). Electrostatic force microscopy (EFM) measurements of the sintered electrospun PTFE membranes revealed the presence of both positive and negative surface charges owing to the transfer of positive charge from PEO which further corroborated by FTIR measurements. To enhance the ensuing triboelectric surface charge, a facile negative charge-injection process was carried out onto the electrospun (ES) PTFE subsequently. The fabricated TENG gave a stabilised peak-to-peak open-circuit-voltage (Voc) of up to ~900 V, a short-circuit current density (Jsc) of ~20 mAm-2 and a corresponding charge density of ~149 μCm-2, which are ~12, 14 and 11 times higher than the corresponding values prior to the ion-injection treatment. This increase in surface charge density is caused by the inversion of positive surface charges with the simultaneous increase in the negative surface charge on the PTFE surface, which was confirmed by using EFM measurements. The negative charge injection led to an enhanced power output density of ~9 Wm-2 with high stability as confirmed from the continuous operation of the ion-injected PTFE/PA6 TENG for 30,000 operation cycles, without any visible reduction in the output. The work thus introduces a relatively simple, cost-effective and environmentally friendly technique for fabricating fibrous fluoropolymer polymer membranes with high thermal/chemical resistance in TENG field and an ion-injection method which is able to dramatically improve the surface charge density of the PTFE fibrous membranes.