High-Performance 3D Nanostructured Silver Electrode for Micro-Supercapacitor Application

Abstract

In the current energy crisis scenario, the development of renewable energy forms such as energy storage systems among the supercapacitors is an urgent need as a tool for environmental protection against increasing pollution. In this work, we have designed a novel 3D nanostructured silver electrode through an antireplica/replica template-assisted procedure. The chemical surface and electrochemical properties of this novel 3D electrode have been studied in a 5 M KOH electrolyte. Microstructural characterization and compositional analysis were studied by SEM, energy-dispersive X-ray spectroscopy, XRD technique, and Kripton adsorption at -198 °C, together with cyclic voltammetry and galvanostatic charge-discharge cycling measurements, Coulombic efficiency, cycle stability, and their leakage current drops, in addition to the self-discharge and electrochromoactive behavior, were performed to fully characterize the 3D nanostructured electrode. Large areal capacitance value of 0.5 F/cm² and Coulombic efficiency of 97.5% are obtained at a current density of 6.4 mA/cm² for a voltage window of 1.2 V (between -0.5 and 0.8 V). The 3D nanostructured silver electrode exhibits excellent capacitance retention (95%) during more than 2600 cycles, indicating a good cyclic stability. Additionally, the electrode delivers a high energy density of around 385.87 μWh/cm² and a power density value of 3.82 μW/cm² and also displays an electrochromoactive behavior. These experimental results strongly support that this versatile combined fabrication procedure is a suitable strategy for improving the electrochemical performances of 3D nanostructured silver electrodes for applications as micro-supercapacitors or in electrochemical devices.

Figure 1

Schematic picture of the subsequent processes for the fabrication of a 3D nanostructured silver electrode: nanoporous alumina template grown during the anodization procedure (a); vacuum thermal evaporation of the Ag seed layer on the top surface of the AAO template forming the nanostructured Ag antidot film platform (b); infiltration of poly(methyl methacrylate) (PMMA) and chloroform (3 g of PMMA in 50 mL of chloroform) solution inside the nanoholes of Ag antidot film platform (c); Al- and Al₂O₃-selective chemical etchings (d); silver electrodeposition for the replicated template (e); and final replica of the 3D nanostructured silver electrode (f).

Figure 2

SEM top-view surface images corresponding to the 3D-NSE before (a) and after (b) the stability tests. EDX microanalysis was performed on the top surface of the 3D-NSE before (c) and after (d) the stability tests.

Figure 3

XRD patterns of the 3D-NSE before (red) and after (blue) the stability tests.

Figure 4

Krypton gas adsorption isotherm measured at 75 K for the 3D-NSE sample.

Figure 5

CV curves of the 3D-NSE measured in 5 M KOH aqueous solution at different scan rates within a potential window ranging from −0.5 V up to 0.8 V with respect to the Ag/AgCl reference electrode (a); variation of the area-specific capacitance with the scan rate (b).

Figure 6

GCD curves of the 3D-NSE at a current density of 6.4 mA cm^–2 (a) and cycle performance of the 3D-NSE during 2600 GCD cycles (b).

Figure 7

Leakage current curve for the 3D-NSE at a voltage value of 0.7 V and kept constant for 2 h (a). Self-discharge curve of the 3D-NSE under open-circuit conditions for 5 h after being charged at a voltage value of 0.7 V and the variation in the charge during the self-discharge process (inset) (b).

Figure 8

Ragone plot showing the classification of the 3D-NSE in comparison to previously reported electrodes used for supercapacitor applications.

Figure 9

Electrochromoactive behavior exhibited by the 3D-NSE during the measurement taken at cyclic voltammetry for a scan rate of 70 mV/s.