All-solid-state flexible supercapacitor based on nanotube-reinforced polypyrrole hollowed structures.

Supercapacitors are strong future candidates for energy storage devices owing to their high power density, fast charge-discharge rate, and long cycle stability. Here, a flexible supercapacitor with a large specific capacitance of 443 F g-1 at a scan rate of 2 mV s-1 is demonstrated using nanotube-reinforced polypyrrole nanowires with hollowed cavities grown vertically on a nanotube/graphene based film. Using these electrodes, we obtain improved capacitance, rate capability, and cycle stability for over 3000 cycles. The assembled all-solid-state supercapacitor exhibits excellent mechanical flexibility, with the capacity to endure a 180° bending angle along with a maximum specific and volumetric energy density of 7 W h kg-1 (8.2 mW h cm-3) at a power density of 75 W kg-1 (0.087 W cm-3), and it showed an energy density of 4.13 W h kg-1 (4.82 mW h cm-3) even at a high power density of 3.8 kW kg-1 (4.4 W cm-3). Also, it demonstrates a high cycling stability of 94.3% after 10 000 charge/discharge cycles at a current density of 10 A g-1. Finally, a foldable all-solid-state supercapacitor is demonstrated, which confirms the applicability of the reported supercapacitor for use in energy storage devices for future portable, foldable, or wearable electronics.

Highly flexible and transparent dielectric elastomer actuators using silver nanowire and carbon nanotube hybrid electrodes.

We demonstrate a dielectric elastomer actuator (DEA) with a high areal strain value of 146% using hybrid electrodes of silver nanowires (AgNWs) and single-walled carbon nanotubes (SWCNTs). The addition of a very small amount of SWCNTs (∼35 ng mm-2) to a highly resistive AgNW network resulted in a remarkable reduction of the electrode sheet resistance by three orders, increasing the breakdown field by 183% and maximum strain, while maintaining the reduction of optical transmittance within 11%. The DEA based on our transparent and stretchable hybrid electrodes can be easily fabricated by a simple vacuum filtration and transfer process of the electrode film on a pre-strained dielectric elastomer membrane. We expect that our approach will be useful in the future for fabricating stretchable and transparent electrodes in various soft electronic devices.