Effects of Nanowire Length on Charge Transport in Vertically Aligned Gold Nanowire Array Electrodes

Abstract

In this study, we demonstrate that vertically aligned gold nanowire array electrodes provide rapid ion and electron transport to the electrode–electrolyte interface. The charge-transport properties of the nanowire electrodes were investigated through cyclic voltammetry, galvanostatic charge/discharge measurements, and electrochemical impedance spectroscopy under a constant-volume device configuration. The total charge stored in the corresponding devices increases monotonically with the length of the nanowires owing to the concomitant increase in the electroactive real surface area of the electrode. A remarkable feature of the electrodes is that the internal resistance associated with charge transport decreases with increasing nanowire length. The electric double-layer capacitance per unit electroactive surface area remains constant up to high charge/discharge rates. Our results demonstrate that charge migration occurs rapidly on the surfaces of the nanowires regardless of their length and the charge/discharge rate used. Thus, vertically aligned nanowire array electrodes show promise as current collectors for next-generation electrochemical energy-storage devices.

Graphite‐Aligned Ni/Ni(OH)2 Nanowire‐Based Aqueous Asymmetric Supercapacitors Exhibiting Excellent Cycle Stability, High Rate Performance, and Wide Operation Voltage

“…In addition, C s was measured at different scan rates and, although it showed a decrease at high scan rates (Figure S3, Supporting Information), the value matched with that obtained from GCD curves. The decrease in C s occurs due to the limitations of electrolyte ions during diffusion and migration within the negative electrode at higher scan rates, although we also noticed much higher energy and power densities than in the symmetric Au nanowire array‐based supercapacitor device (measured at different current densities from GCD curves) (Figure S3, Supporting Information) …”

“…Stability at high scan rates can be attributed exclusively to the high charge transfer rate in the nanowires‐based electrode. We have also previously shown that a symmetric supercapacitor device comprised of two Au nanowire array electrodes is very stable at high scan rates . The rapid charge transport through the metallic nanowires allows the charge carriers to easily move across the nanowire surface, resulting in the formation of an electric double layer at even high charge/discharge rates.…”

“…Metal nanowires can provide unique advantages in supercapacitors due to their high specific area, high electrode‐electrolyte contact region, and swift electron transfer mechanism resulting from their highly conductive metallic conduits . In metallic nanowires, shortened ion diffusion lengths result in improved rate performance ( t=l 2 /D ), where t and l are the time required for ions to diffuse through the electrode material and diffusion length, respectively, and D is the diffusion coefficient .…”

“…In metallic nanowires, shortened ion diffusion lengths result in improved rate performance ( t=l 2 /D ), where t and l are the time required for ions to diffuse through the electrode material and diffusion length, respectively, and D is the diffusion coefficient . These features result in high charge/discharge rates . However, the metal nanowires that store charge via the formation of electric double layers have relatively low capacitance when compared to electrodes involving faradaic charge transfer processes during charge storage.…”

“…Previously, we have shown that using a gold nanowire array‐based architecture in a symmetric supercapacitor electrode can be beneficial for achieving very high charge transfer rates . In order to increase capacity, these nanowires were coated with a conducting polymer shell to introduce pseudocapacitance in the device .…”