No abstract

flexible and stretchable energy-storage batteries and supercapacitors suitable for wearable electronics are at the forefront of the emerging field of intelligent textiles. In this context, the work here presented reports on the development of a symmetrical wire-based supercapacitor able to use the wearer's sweat as the electrolyte. the inner and outer electrodes consists of a carbon-based thread functionalized with a conductive polymer (polypyrrole) which improves the electrochemical performances of the supercapacitor. The inner electrode is coated with electrospun cellulose acetate fibres, as the separator, and the outer electrode is twisted around it. the electrochemical performances of carbon-based supercapacitors were analyzed using a simulated sweat solution and displayed a specific capacitance of 2.3 F.g −1 , an energy of 386.5 mWh.kg −1 and a power density of 46.4 kW.kg −1. Moreover, cycle stability and bendability studies were performed. Such energy conversion device has exhibited a stable electrochemical performance under mechanical deformation, over than 1000 cycles, which make it attractive for wearable electronics. finally, four devices were tested by combining two supercapacitors in series with two in parallel demonstrating the ability to power a LeD. Wearable electronic devices have emerged in the last decade due to a remarkable interest in intelligent textiles or electronic skin applications. Transistors, memory devices, organic light emitting diodes, triboelectric and energy storages devices have been produced in flexible substrates enabling conformity to curved surfaces 1. Among the storage devices proposed, the fibre device is the most attractive as it can be incorporated directly on textiles or other wearable applications 2. Therefore, numerous works have focused on the development of fibre-based capacitors and supercapacitors 3-6. These devices can be produced in sheets and rolled out to have a fibre geometry. Kim and co-workers 7 have tested a carbon fibre paper as electrode reaching a specific capacitance of 140 F.g −1 and 90% of capacitance retention after 5000 cycles using 0.5 M H 2 SO 4 as electrolyte and Ag/AgCl as the reference electrode. They have further improved these performances with decorated Polypyrrole-NiCo 2 O 4 carbon paper 8 reporting specific capacitance of 900 F.g −1 (at 1A), and 88% of capacity retention (5 A.g −1) after 10,000 cycles. Silver nanodendritic cellulose acetate electrodes were tested by Kesavan Devarayan 9 in the form of flexible sheets showing specific capacitance in the range of 125 F.g −1 after 1000 cycles and a capacitance retention around 20%. Single-walled carbon nanotube/polyaniline (SWCNT/PANI) nanoribbon paper with volumetric capacitance (40.5 F.cm −3) and mechanical compliance toward bending and folding, maintaining electrochemical stability up to 1000 cycles has been reported by Dengteng Ge 10. The fabrication of a yarn of carbon nanotubes filaments with 23 µm diameter for electrodes of supercapacitors has been reported by F. Liu 11 and co-workers. ...

Developments in thermoelectric (TE) transparent p-type materials are scarce and do not follow the trend of the corresponding n-type materials – a limitation of the current transparent thermoelectric devices. P-type thermoelectric thin films of CuI have been developed by three different methods in order to maximise optical transparency (>70% in the visible range), electrical (σ = 1.1 × 104 Sm−1) and thermoelectric properties (ZT = 0.22 at 300 K). These have been applied in the first planar fully transparent p-n type TE modules where gallium-doped zinc oxide (GZO) thin films were used as the n-type element and indium thin oxide (ITO) thin films as electrodes. A thorough study of power output in single elements and p-n modules electrically connected in series and thermally connected in parallel is inclosed. This configuration allows for a whole range of highly transparent thermoelectric applications.

Simultaneously transparent and flexible conductive materials are in demand to follow the current trend in flexible technology. A highly transparent and flexible thermoelectric generator of 17 p–n modules was constructed based on copper iodide thin films.