Synergistic Effect of Nickel and Cobalt in Nanowire Array for High Energy Storage with Rapid Charge Transfer in Asymmetric Supercapacitor

Abstract

We introduce a unique asymmetric supercapacitor design that combines a vertically aligned Ni−Co alloy‐type nanowire (NiCoNW) array electrode with a graphene flakes (GFs) electrode. The sandwiching of these two electrodes enables the device to operate at a high working potential window of 2.0 V. The improved response of the device is attributed to the asymmetric design and a high charge transfer in the NiCoNWs compared with pure metals. The optimized presence of Co in the alloy increases the rate of hydroxide formation in an alkaline solution during the gas evolution reaction. The use of GFs to modify the graphite electrode (GFs@Graphite) provided a more stable response at high current densities. We obtain extremely stable cyclic voltammetry (CV) plots even at very high scan rates (500 V/s) and galvanostatic charge–discharge curves with longer charge–discharge times. The highest capacitance achieved for the assembled device (Asy‐NiCoNWs/GFs@Graphite) is 339 F/cm3 (volumetric) at a current density of 5.0 A/cm3. In addition, a remarkable cycling retention of ∼100 % is observed after 10000 continuous potential cycles.

Core–Shell Ni/Ni(OH)2 Nanowire Array for Asymmetric Supercapacitors

“…As we have done previously, with NiNWs and NiCoNWs, the three-electrode electrochemical response was first recorded for NiNWs having varying heights (NiNW arrays as the working electrode). , For the measurements, Ag/AgCl served as a reference electrode, and a Pt wire served as a counter electrode in an electrolyte solution of 0.5 M KOH. The data obtained from this experiment were used for the mass balance procedure for the asymmetric supercapacitor.…”

“…GFs were synthesized through an electrochemical exfoliation process, as detailed in our prior work. , In a nutshell, GFs were synthesized using an electrochemical exfoliation method with 0.1 M H 2 SO 4 as the electrolyte and exfoliating agent. The process involved applying dc potential to a graphite foil electrode, resulting in the formation of a stable GF suspension after several washing and ultrasonic treatment steps.…”

“…Typically, anodic aluminum oxide (AAO) membranes with varying pore sizes of 35, 100, and 150 nm were used for electrochemical deposition of Ni. We used a mixture of Ni­(II) sulfate hexahydrate, Ni­(II) chloride hexahydrate, and boric acid in 5 mL of water as the Ni plating solution. , In accordance with the principle that the quantity of deposited metal corresponds directly to the charge applied during the deposition procedure, we employed distinct charge values for the electrochemical deposition of NiNWs possessing varied heights. Specifically, we generated NiNWs measuring 35 and 100 nm in diameter while maintaining a consistent height of 11 μm for both.…”

“…Shortened ion diffusion lengths translate to faster diffusion times, enabling quicker charge and discharge processes . This phenomenon is quantified by the equation t = l 2 / D , where t represents the time needed for ions to diffuse through the electrode material, l signifies the ion diffusion length, and D denotes the diffusion coefficient. ,, A smaller diffusion length and a larger diffusion coefficient result in reduced diffusion times, and consequently, enhanced charge/discharge rates are observed. In addition, the rapid charge/discharge rates attributed to metal nanowires are also a result of their combination of characteristics: a generous electrode–electrolyte contact interface, efficient electron transfer, and shortened ion diffusion lengths coupled with a high diffusion coefficient.…”