Electrodeposited fabrication of highly ordered Pd nanowire arrays for alcohol electrooxidation

Abstract

Highly ordered Pd nanowire arrays (NWAs) are prepared using a porous aluminum oxide template by pulse electrodeposition. The obtained Pd nanowire arrays with the diameter of 50 nm and length of 850 nm have been characterized by scanning electron microscopy, energy dispersive X-ray analysis, and high resolution transmission electron microscope. Meanwhile, the electrocatalytic activity of Pd NWAs electrodes for methanol and isopropanol oxidation in alkaline media is studied. It is found that the obtained nanostructures exhibit excellent catalytic activity for alcohol electrooxidation. The isopropanol oxidation shows the higher activity on Pd NWAs electrode than methanol in alkaline medium.

Introduction

Nanostructured materials have become the focus of intensive research in the areas of catalysis, electroanalysis, sensors, luminescence, and gas storage [1], [2], [3]. From the viewpoint of practical applications, the ordered, high surface area structures of materials such as nanowire arrays (NWAs) display highly chemical reactivity because of their excellently physical and chemical properties [4], [5], [6]. For instance, it is found that Ni–Pt multilayered nanowire arrays demonstrated enhanced coercivity and high remanence ratio [7]. Zhao et al. also observed that Pt nanowire arrays had enhanced electrocatalytic activity toward methanol oxidation [8]. Chen et al. have investigated the structure and electrochemical properties of arrayed carbon nanotube (CNT)-platinum nanoparticle composites and cyclic voltammograms show well-behaved curves in methanol oxidation on Pt/CNT [9].

At present, the developed strategies for the preparation of nanowire arrays include hard template and soft template synthesis. Among these methods, the combination of porous anodic aluminum oxide (AAO) template with electrodeposition is an effective and powerful method for obtaining metal highly ordered NWAs with uniform and tunable structures [10], [11], [12], [13], [14]. Furthermore, the distribution patterns of pore size in AAO template can directly influence the diameters of NWAs, which can be easily controlled by monitoring preparation conditions, such as temperature and oxidation voltage. Thus, it is also a powerful technique for the deposition of metals with different sizes.

In this work, we report the successful fabrication of the highly ordered Pd NWAs with uniform diameter of about 50 nm and length of 850 nm by the AAO template electrodeposition method. The electrocatalytic activity of Pd NWAs electrode toward the electrooxidation of methanol and isopropanol is investigated. Isopropanol is the smallest secondary alcohol, less toxic than methanol and its electrochemical oxidation is of great interest due to its particular molecular structure. And the electrooxidation of alcohol can be applied on fuel cells and sensors. In previous reports, electrocatalysts for electrooxidation of alcohol were usually noble metal Pt-based materials such as Pt or Pt-based alloys NWAs [15], [16], [17], [18], [19], [20], [21], [22], [23]. Due to the limited source of Pt, there has been an intense search for less expensive, more effective non-Pt electrocatalysts that can offer acceptable performance. Thus, the activity of isopropanol oxidation on Pd has been studied and shows higher activity than that on Pt [24]. Here, we firstly use the Pd NWAs as the electrocatalysts for methanol and isopropanol oxidation.