Abstract
Energy autonomy is critical for wearable and portable systems and to this end storage devices with high‐energy density are needed. This work presents high‐energy density flexible supercapacitors (SCs), showing three times the energy density than similar type of SCs reported in the literature. The graphene–graphite polyurethane (GPU) composite based SCs have maximum energy and power densities of 10.22 µWh cm−2 and 11.15 mW cm−2, respectively, at a current density of 10 mA cm−2 and operating voltage of 2.25 V (considering the IR drop). The significant gain in the performance of SCs is due to excellent electroactive surface per unit area (surface roughness 97.6 nm) of GPU composite and high electrical conductivity (0.318 S cm−1). The fabricated SCs show stable response for more than 15 000 charging/discharging cycles at current densities of 10 mA cm−2 and operating voltage of 2.5 V (without considering the IR drop). The developed SCs are tested as energy storage devices for wide applications, namely: a) solar‐powered energy‐packs to operate 84 light‐emitting diodes (LEDs) for more than a minute and to drive the actuators of a prosthetic limb; b) powering high‐torque motors; and c) wristband for wearable sensors.
Highlights
Energy autonomy is critical for wearable and portable systems and to this based energy storage technologies have been explored meet the demand in end storage devices with high-energy density are needed
Surface morphology of GS (Figure 2a,b) and graphite polyurethane (GPU) (Figure 2c,d) films have been characterized by scanning electron microscopy (SEM)
SEM results reveal that the morphology of GPU composite is rough, exhibiting a layered structure consisting of graphite microflakes (Figure 2c,d)
Summary
Surface morphology of GS (Figure 2a,b) and GPU (Figure 2c,d) films have been characterized by scanning electron microscopy (SEM). GPU Raman spectrum (Figure 3b) exhibits a small D peak centered around 1345 cm−1, arising from the existence of structural defects.[39] The ratio between D and G peak intensities (ID/IG) resulted in 0.16, confirming the formation of the small graphitic domains in the structure.[39] Comparing 2D bands of GPU and GS films (Figure 3b), an energy shift from 2716 cm−1 (GS) to 2708 cm−1 (GPU), i.e., around 8 cm−1, is observed The origin of this shift is caused by the influence of the PU resin in the heterostructure composites.[39]. The peaks at 1121 and 1069 cm−1 correspond to the polyester’s C O group.[39,40] The presence of amine and hydroxyl group shows that more ions can be attached into the lattice of the graphite-PU matrix,[40] which further enhance the performance of the SC, as it will be demonstrated later
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