High performance aqueous asymmetric supercapacitor based on iron oxide anode and cobalt oxide cathode
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We develop an asymmetric aqueous supercapacitor using iron oxide anode and cobalt oxide cathode. The anode was fabricated using electrospinning of carbon precursor/iron oxide precursor blend followed by pyrolysis and in situ electrochemical conversion (to oxide) to form the binderfree and freestanding composite anode which delivered a capacitance of 460 F/g at 1 A/g and retained 82% capacitance after 5000 cycles. The superior performance is attributed to easy electrolyte accessibility as well as the porous fibrous carbon morphology, facilitating volume expansion of iron oxide. The cobalt oxide cathode was prepared using a simple chemical synthesis technique. The electrodes were chosen based on high over potential to water splitting reactions in 6 M KOH electrolyte resulting in a potential window of 1.6 V. The asymmetric device operated in 1.6 V achieved a capacitance of 94.5 F/g at 0.5 A/g while retaining 75% of its capacitance after 12,000 cycles, delivering energy and power densities of 40.53 W h/kg and 2432 W/kg, respectively.
I. INTRODUCTION
Rise in energy demands and scarcity of fossil fuels have compelled us towards the development of sustainable energy systems and innovation of high energy storage devices.1 Consequently, there is an urgent demand for efficient energy storage devices, which are of low cost and are environmentally friendly. Among the various energy storage devices, supercapacitors and nextgeneration batteries have gained considerable attention. Recent developments in the field of supercapacitors have arisen, as they possess attractive properties such as fast charge–discharge periods, wide operational window, and excellent cyclability.2 The prevenient properties make them promising candidates for energy storage applications in various fields viz, portable electronics, regenerative braking systems in hybrid vehicles, and backup power supplies.3 Ragone plot, which correlates power density and energy density of various energy storage devices, shows that supercapacitors possess higher energy density than traditional capacitors and higher power density than batteries/fuel cells, bridging the gap between a traditional capacitors and batteries.1,4–7 Based on the charge storage mechanism in supercapacitors, they can be divided into two classes: electrical double-layer capacitors (EDLCs) that are based on charge separation and accumulation at the electrode/electrolyte interface and pseudocapacitors that rely on fast redox or Contributing Editor: Tianyu Liu a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2018.13
intercalation reaction of the electrode material.1,6,8–11 The EDLCs are usually based on porous carbons, hence electrodes possess lower specific capacitance. On the other hand, pseudocapacitors exhibit high specific capacitance (;1000 F/g), several times higher than the EDLCtype supercapacitors because of higher levels of charge storage occurring from redox reactions, which shows a great interest for future applications.1,6,11 The specific energy (E) of supercap
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