Vertically aligned catalysts comprised of platinum–nickel thin films on nickel nanorods (designated as Pt–Ni@Ni-NR) with varying ratios of Pt to Ni in the thin film were prepared by magnetron sputtering and evaluated for their oxygen reduction reaction (ORR) activity. A glancing angle deposition (GLAD) technique was used to fabricate the Ni nanorods (NRs) and a small angle deposition technique for growth of a thin conformal coating of Pt–Ni on the Ni-NRs. The Pt–Ni@Ni-NR structures were deposited on glassy carbon for evaluation of their ORR activity in an aqueous acidic electrolyte using the rotating disk electrode technique. The Pt–Ni@Ni-NR catalysts showed superior area-specific and mass activities for ORR compared to those of Pt–Ni alloy nanorod catalysts prepared using the GLAD technique and compared to those of conventional large-surface area Pt and Pt–Ni alloy nanoparticle catalysts.

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Fuel cell technology is one of the solutions which can play an important role in the environmentally friendly with more efficient, cleaner and quieter than traditional internal combustion engines. Among the fuel cells types polymer electrolyte membrane fuel cells have many advantages regarding quick start-up time, less warm-up time high power density and high efficiency. There are still some limitations due to the cost of Pt-based catalysts. Platinum based catalysts are presently the most promising catalysts for Oxygen Reduction Reaction (ORR) in Fuel Cells. Homogenously distributed Pt nanoparticles on carbon support (Pt/C) nanoparticles are mostly using in conventional way to produce Fuel Cells. Pt-based electrocatalysts with higher activity and durability are needed for cost-competitive PEM Fuel Cells. It can be developed/improved further by using Platinum-based/alloy thin film core-shell nanostructures. For this reason, this article reviewed the significance and processing of such core/shell structures. The general information about Fuel Cells is given at the beginning of this review article. Later, type of the fuel cells along with more definition of the PEM Fuel Cells are described. The Pt shell on Ni, Cr, Pd, Ru, and WC core nanorods increase the stability and durability and decrease the cost based on the published works. This nanostructured design will significantly impact the fuel cell technology by improving catalysts. Specifically, by controlling size, composition, and surface-area-to-volume ratios, this review article describes the investigation of the core/shell nanostructured array catalysts. A few of the following examples of core/shell structures and supported catalysts proved electrocatalytic oxygen reduction.

In this study, we developed a stacked core−shell nanorod array electrocatalyst design to improve oxygen reduction reaction (ORR) kinetics and catalyst stability for polymer electrolyte fuel cell (PEMFC) applications. For this purpose, we fabricated two-layer stacked nanorod arrays with each layer consisting of a tungsten carbide (WC) core and a platinum−nickel (Pt−Ni) alloy shell. WC nanorods were grown by a glancing angle deposition (GLAD) method. Then, WC nanorods were coated with a Pt−Ni shell conformally by a highpressure sputtering (HIPS) method. This process was repeated twice to form the second layer of the stack. We investigated three different Pt:Ni ratios including 3:7, 1:1, and 3:1. Cyclic voltammetry (CV) and rotating disk electrode (RDE) methods were used for electrochemical characterization of the Pt:Ni/WC electrodes in a 0.1 M HClO 4 electrolyte solution. Morphological and crystallographic analyses were performed using scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. Pt mass loading values were measured using a quartz crystal microbalance. Electrochemically active surface area (ECSA) values change in the order of 3:7 > 1:1 > 3:1 in the Pt:Ni ratio. Specific activity (SA) and mass activity (MA) were higher for the 3:7 composition after accelerated stability tests were comparable to those of other compositions.

The quality of the shell coating around nanorods is critical in device applications. Conventional physical vapor deposition (PVD) techniques can be utilized for highly conformal shell coating formation in core-shell structure devices. To identify scalable fabrication techniques for conformal shell coatings, Monte Carlo (MC) simulations of PVD growth were performed under different atomic flux distributions and angles on arrays of glancing angle deposition (GLAD) nanorods, which were also generated by MC simulations. We investigated the conformality of PVD films (shell) around GLAD rod arrays (core) and analyzed the thickness uniformity of the shell layer across the sidewalls of rods. Our results show that Angular Flux-Normal Angle (A-NAD), which might correspond to high-pressure sputter deposition at normal incidence (HIPS at θ = 0o) can generate better conformal shell coating compared to others. In Uniform Flux-Normal Angle technique (U-NAD), which corresponds to a thermal evaporation deposition, the growth suffers from poor sidewall coverage. In addition, introducing a small angle to the flux also improves the shell conformality. Therefore, high-pressure sputter deposition technique is expected to provide superior conformality for a catalyst or semiconductor coating around base nanorods, for example for fuel cell and solar cell applications, with the help of obliquely incident atoms of the HIPS flux.