Flexible, water-proof, wire-type supercapacitors integrated with wire-type UV/NO2 sensors on textiles

Abstract Wire-type devices that can be integrated onto fabrics are being actively studied to meet the demands for various wearable systems. In this study, we report the fabrication of wire-type supercapacitors (WSCs) integrated with wire-type UV/NO2 sensors on textiles. The WSC consists of braided carbon fiber electrodes coated with multi-walled carbon nanotubes (MWNT)/V2O5 nanowires(NWs), a cellulose-based separator, and an ionic-liquid-based electrolyte of [EMIM][TFSI]/LiCl/Al2O3 nanoparticles. This fabricated WSC exhibited good performance with an extended potential window of 1.5 V and areal capacitance of 10.6 mF/cm2 at 0.5 mA/cm2. Very stable electrochemical performance of the WSC was also observed under mechanical deformations of bending, knotting, and folding. In addition, stable WSC performance in water was demonstrated by encapsulation with a thermally-shrinkable tube. Furthermore, μ-light-emitting diodes and wire-type NO2 gas and UV sensors were operated by the integrated multiple WSCs on a textile: The MWNT-coated wool wire detected NO2 gas reproducibly by increase of the current. Using spiropyran and ZnO NWs, changes in both color and photo-current were detected upon UV irradiation. This work demonstrates the great potential of our WSC for use in wearable textile sensor systems as an efficient energy storage device.