Electrochemical Behavior of Cobalt Oxide/Boron-Incorporated Reduced Graphene Oxide Nanocomposite Electrode for Supercapa
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Electrochemical Behavior of Cobalt Oxide/BoronIncorporated Reduced Graphene Oxide Nanocomposite Electrode for Supercapacitor Applications R. Naresh Muthu and Sankara Sarma V. Tatiparti (Submitted April 30, 2020; in revised form September 3, 2020; Accepted September 27, 2020) Electrodes from hydrothermally synthesized boron-incorporated reduced graphene oxide (B-rGO), Co3O4, and Co3O4/B-rGO nanocomposites are tested in 2 M KOH and NaOH electrolytes for supercapacitor applications. Structural characterization was done by x-ray diffraction and x-ray photoelectron spectroscopy. Cyclic voltammogram of B-rGO indicates partial electrical double-layer capacitance and pseudocapacitive behaviors. Co3O4, shows two reversible redox peaks, indicating diffusion-controlled (batterylike) process. Interestingly, Co3O4/B-rGO possesses both the pseudocapacitive and diffusion-controlled features. The specific capacitance (Csp) from galvanostatic charge/discharge experiments is higher in all the electrodes in KOH than in NaOH. Co3O4/B-rGO shows the highest Csp of 600 F g−1 (270 C g−1) at 0.1 A g−1 and 454 F g−1 (204 C g−1) at 10 A g−1 in KOH. Co3O4/B-rGO-KOH system retains 87.8% capacitance after 2000 cycles, demonstrating very good cyclic stability. Co3O4/B-rGO-KOH system yields, a remarkable, maximum power density of 2250 W kg−1 with an energy density of 12.77 W h kg−1 at 10 A g−1. The better performance in KOH is attributed to the low hydration sphere radius, high ionic conductivity of K+, low diffusive and charge transfer and electrode resistance, estimated from electrochemical impedance spectroscopy. The electrode–electrolyte combination is crucial for the overall performance as a supercapacitor electrode.
Keywords
battery-like, B-rGO, Co3O4/B-rGO, cobalt oxide, EDLC, supercapacitor
1. Introduction The depletion of fossil fuels and increasing energy demand have triggered research in alternative energy and power sources. Supercapacitors can yield high power density and possess long cyclic stability (Ref 1). They are classified broadly into two types based on the charge storage mechanism: (i) nonFaradaic (i.e., electrical double-layer capacitors or EDLCs) and (ii) Faradaic (i.e., diffusion-controlled or battery-like involving reversible redox reactions) (Ref 2, 3). Carbon-based materials, viz. activated carbon (Ref 4), carbon nanotubes (Ref 5, 6), carbon nanofiber (Ref 7) and graphene (Ref 8, 9), are used as EDLC electrodes because of their high surface area and tunable surface properties (Ref 411). For example, the activated carbon synthesized from cap and stalk of mushrooms through microwave-induced method resulted in a specific capacitance (Csp) 271.94 and 269.66 F g−1 at 0.5 A g−1 (Ref 12). The power density and cycle life of these Electronic supplementary materialThe online version of this article (https://doi.org/10.1007/s11665-020-05176-z) contains supplementary material, which is available to authorized users. R. Naresh Muthu and Sankara Sarma V. Tatiparti, Department of Energy Science and
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