Graphene–Graphite Polyurethane Composite Based High‐Energy Density Flexible Supercapacitors

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. A graphene–graphite polyurethane resin composite based flexible supercapacitor shows excellent electrochemical and supercapacitive performance. The graphite‐polyurethane composite offers increased electroactive surface per unit area, less hydrophobicity, and excellent surface charge distribution. The supercapacitor, with excellent capacitance (15 mF cm–2), operating voltage (≈2.25 V), and high energy and power densities (10.22 μW h cm–2 and 11.15 mW cm–2 respectively), is shown to have applications in wearable systems, robotics, and prosthetics.