High energy density, robust and economical supercapacitor with poly(3,4-ethylenedioxythiophene)-CO2 activated rice husk derived carbon hybrid electrodes

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High energy density but not at the expense of power density, large areal and gravimetric capacitances, durability, lightweight, ease of fabrication, low self-discharge rates, low cost, eco-friendly, non-hazardous components to enable scale-up and safe disposal are the desirable pre-requisites that supercapacitors are expected to satisfy so that they can bridge the gap between batteries and sole carbon based supercapacitors. These requirements are met in a hybrid based on poly(3,4-ethylenedioxythiophene) (PEDOT) fibers, a robust, inexpensive, easily processable conducting polymer, with an another remarkably cheap, CO2 activated carbon (CO2@C) derived from rice husk, a waste by-product of rice manufacturing, which is abundantly available (for two-thirds of the world's population consumes rice). The PEDOT-CO2@C hybrid based symmetric flexible supercapacitor delivers gravimetric and areal capacitances of 458 F g−1 (at 1 A g−1) and 850 mF cm−2 over a wide voltage window of 2.1 V, an equilibrated low leakage current of 0.14 μA, an exceptionally high energy density of 280 Wh kg−1 at a power density of ∼1 kW kg−1, a low diffusion resistance of 3 Ω and a capacitance retention of ∼98% over 5000 cycles. These performance metrics are significantly superior to that exhibited by symmetric cells of sole CO2@C or PEDOT electrodes. This study shows that the PEDOT-CO2@C hybrid overcomes the major limitations that a majority of the lab-level supercapacitors suffer from: low energy density and a processing methodology that is cost effective and scalable simultaneously.Three charged PEDOT-CO2@C hybrid based symmetric supercapacitors are connected in series. Using this assembly, red and yellow LEDs are illuminated, and a commercial glucometer is powered by replacing the 3 V battery with the hybrid supercapacitors. The latter demonstration opens up an exciting possibility of powering a range of micro-diagnostic devices with this easy to use, handle and dispose hybrid supercapacitors instead of toxic, difficult to dispose- batteries.