The electrocatalytic oxygen reduction reaction (ORR) activity of vertically-aligned Pt nanorods has been evaluated utilizing cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques in a 0.1 M HClO 4 solution at temperatures ranging from 20 to 60 C. A glancing angle deposition (GLAD) technique was used to fabricate Pt nanorod arrays on glassy carbon (GC) electrodes. GLAD catalyst nanorods, without any carbon support, have been produced at different lengths varying between 50 and 400 nm, corresponding to 0.04-0.32 mg/cm 2 Pt loadings, with diameter and spacing values ranging from about 5 up to 100 nm. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD) results reveal that Pt nanorods are well-isolated, vertically aligned, and single-crystal. Crystal orientation analysis demonstrates that large surface area Pt nanorod sidewalls are mainly dominated by Pt(110) planes, which is known to be the most active crystal plane of Pt for the ORR. Compared to a commercial high-surface-area-supported Pt (Pt/C) catalyst, the CV results show that the Pt-nanorod electrocatalyst exhibits a more positive oxide reduction peak potential, indicating that GLAD Pt nanorods are less oxophilic. Moreover, the nanorods exhibit enhanced stability against loss of electrochemically-active surface area as a result of potential cycling in acidic electrolyte as compared to the Pt/C catalyst. Specific ORR activities determined by the RDE technique for GLAD Pt nanorods of different lengths are analyzed and compared to literature values for polycrystalline Pt, nano-structured thin film Pt (3M NSTF Pt), and to those measured for Pt/C. RDE results reveal that Pt-nanorod electrocatalysts exhibit higher area-specific activity, higher electron-transfer rate constant, and comparable activation energy for ORR than those of Pt/C due to their larger crystallite size, single-crystal property, and dominance of the preferred crystal orientations for ORR. However, Pt nanorods show lower mass specific activity than that of Pt/C electrocatalyst due to the large diameter of nanorods.

Vertically aligned platinum–nickel (Pt–Ni) alloy nanorod arrays were grown on glassy carbon electrodes using a magnetron sputtering glancing angle deposition (GLAD) technique. X-ray diffraction and electron microscopy results show that the as-deposited nanorods are alloys and that the alloy composition and geometric properties of Pt–Ni nanorods can be changed by controlling the GLAD deposition parameters. The GLAD Pt–Ni nanorod electrodes were investigated as potential electrocatalysts for the oxygen reduction reaction (ORR) in polymer electrolyte fuel cells (PEFCs) using cyclic voltammetry (CV) and rotating-disk electrode (RDE) techniques in aqueous perchloric acid electrolyte. The electrochemically active surface area (ECA), determined from the charge for hydrogen adsorption and desorption in the CVs, was estimated to be a factor of 3 or more larger than the geometric surface area of the nanorods. The ORR mass-specific activity of the Pt–Ni nanorods was found to be a factor of 2.3–3.5 higher than that of pure Pt nanorods of the same dimensions and increase with increasing Ni content, whereas ORR area-specific activity enhancement was only observed for the nanorods with the highest Pt content. In addition, the Pt–Ni nanorods were found to have higher stability against loss of ECA during potential cycling than Pt nanorods and conventional high-surface-area-carbon-supported Pt nanoparticles.

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Vertically aligned chromium nanorod arrays were grown on glassy carbon electrodes by a dc magnetron sputtering glancing angle deposition (GLAD) technique. The Cr nanorods were used as low-cost, high surface area, metallic supports for a conformal Pt thin film, resulting in a potential low-loading electrocatalyst for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cells. Conformal coatings of Pt on Cr nanorods were achieved using a dc magnetron sputtering small angle deposition (SAD) technique. The electrocatalytic ORR activity of SAD-Pt/GLAD-Cr electrodes was investigated using cyclic voltammetry and rotating-disk electrode techniques in a 0.1 M HClO 4 solution at temperatures ranging from 20 to 60 • C, and was compared to those of GLAD Cr nanorods coated with Pt thin film deposited at normal and large angles of incidence. The results show that SADPt/GLAD-Cr nanorods exhibit higher values of electrochemically-active surface area (ECSA), area-and mass-specific activities, and better stability against loss of ECSA during potential cycling in the acidic electrolyte. The improved ORR activity and enhanced catalyst utilization of SAD-Pt/GLAD-Cr electrode might be attributed to a better Pt conformality, especially at the sidewalls of the nanorods, and a preferential exposure of certain crystal facets.

Introducing a hydrophobic property to vertically aligned hydrophilic metallic nanorods was investigated experimentally and theoretically. The platinum nanorod arrays were deposited on flat silicon substrates using a sputter glancing angle deposition technique (GLAD). Then a thin layer of Teflon (nanopatch) was partially deposited on the tips of platinum nanorods at a glancing angle of theta(dep) = 85 degrees for different deposition times. Teflon deposition on Pt nanorods at normal incidence (theta(dep) = 0 degrees) was also performed for comparison. Morphology and elemental analysis of Pt/Teflon nanocomposite structures were carried out using scanning electron microscopy (SEM) and energy dispersive x-ray analysis (EDAX), respectively. It was found that the GLAD technique is capable of depositing ultrathin isolated Teflon nanostructures on selective regions of nanorod arrays due to the shadowing effect during obliquely incident deposition. Contact angle measurements on nanocomposite Pt nanorods with Teflon nanopatches exhibited contact angle values as high as 138 degrees, indicating a significant increase in the hydrophobicity of originally hydrophilic Pt nanostructures that had an angle of about 52 degrees. The enhanced hydrophobicity of the Pt nanorod/Teflon nanopatch composite is attributed to the presence of nanostructured Teflon coating, which imparted a low surface energy. Surface energy calculations were performed on Pt nanorods, Teflon thin film, and Pt/Teflon composite using the two-liquid method to confirm the contact angle measurements. Furthermore, a new contact angle model utilizing Cassie and Baxter theory for heterogeneous surfaces was developed in order to explain the enhanced hydrophobicity of Pt/Teflon nanorods. According to our model, it is predicted that the solid-liquid interface is mainly at the Teflon tips when the composite nanorods are in contact with water.