Electrochemical Characterization of Platinum Nanotubules Made via Template Wetting Nanofabrication

Standard oxidation-reduction reactions such as those of ferrocyanide and ferrocene have long been employed in evaluating and comparing new electrode structures with more traditional configurations. A variety of nanostructured carbon electrodes developed in recent years have been reported to exhibit faster electron transfer kinetics than more traditional carbon structures when studied with these redox reactions. This type of comparison has not been widely explored for nanostructured platinum electrodes that have become increasingly common. In this work, a platinum nanotubule array electrode was fabricated via a simple template-based process and evaluated using the standard ferrocyanide redox reaction. The nanotubule array electrodes were observed to more closely approach ideal reversible behavior than a typical Pt black/Nafion fuel cell electrode or a standard polished Pt disc electrode. The apparent heterogeneous electron transfer coefficient was determined using the Nicholson method and found to be one to two orders of magnitude greater for the nanotubule array electrodes, depending on the diameter of the nanotubules, in comparison with these same two more traditional electrode structures. 1. Introduction Metal nanowires, rods, tubes, and other so-called “one-dimensional nanostructures” [1–3] have drawn increasing attention due to their unique properties. Among the wide variety of methods reported for fabrication of such nanostructures are template-based methods [2, 4–8]), electrospinning [9], deposition onto nanowire or nanofiber supports [10–12], and others [13–15]. One-dimensional carbon and metallic nanostructures have shown promise in electrocatalytic applications, such as in small fuel cells and electrochemical sensors. Beyond their high surface-to-volume ratio, these nanostructures present many potential advantages in electrocatalytic applications, including fewer diffusion impeding interfaces with polymeric binders, more facile pathways for electron transfer, and more effective exposure of active surface sites. Standard redox reactions such as those of ferrocyanide or ferrocene have long been employed as benchmarks in evaluating various carbon [16] and platinum [17–20] electrode structures, preparation techniques, and surface treatments. While carbon nanotube-based electrodes have been widely evaluated in this manner [21–25], electrochemical studies of platinum nanostructures have focused on organic molecules important to fuel cells (e.g., methanol and formic acid) [3, 8, 26] or various biosensor applications [1, 27]. Comparison of results for