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.
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.
Applications such as batteries, fuel cells, solar cells, and sensors, can benefit from high surface-to-volume ratio core/shell arrays of nanorods. The fabrication of the conformal shell layers on nanorod arrays has been a formidable task. In order to assess the deposition conditions for the production of conformal shell coatings by physical vapor deposition (PVD) techniques, we employed Monte Carlo (MC) simulations that involved shell depositions under different flux distributions and angles on arrays of rods. We investigated the conformality of PVD shell layers on nanorod arrays of different aspect ratios, which is defined to be the ratio of rod height to the gaps between nearest-neighbor rods. MC simulated core/shell structures were analyzed for the thickness uniformity of the shell layer across the sidewalls of rods. Our results show that a small angle deposition approach involving a uniform oblique flux (U-SAD) with a small incidence angle ≤ 30o can generate a fairly conformal shell coating around small aspect-ratio rods. However, normal angle deposition with an angular flux distribution (A-NAD) achieves superior conformality both on small and high-aspect-ratio structures compared to U-SAD, conventional uniform normal angle deposition (U-NAD), and SAD with an angular flux distribution (A-SAD). A-NAD can be realized in a PVD system such as by high pressure sputter deposition; while U-SAD can be achieved in thermal evaporation system with a small angle incident flux. In addition, U-NAD and A-SAD can correspond to film growth by normal incidence thermal evaporation and SAD-high pressure sputter deposition, respectively.
Chemical removal of materials from the surface is a fundamental step in micro- and nano-fabrication processes. In conventional plasma etching, etchant molecules are non-directional and perform a uniform etching over the surface. However, using a highly directional obliquely incident beam of etching agent, it can be possible to engineer surfaces in the micro- or nano- scales. Surfaces can be patterned with periodic morphologies like ripples and mounds by controlling parameters including the incidence angle with the surface and sticking coefficient of etching particles. In this study, the dynamic evolution of a rippled morphology has been investigated during oblique angle etching (OAE) using Monte Carlo simulations. Fourier space and roughness analysis were performed on the resulting simulated surfaces. The ripple formation was observed to originate from re-emission and shadowing effects during OAE. Our results show that the ripple wavelength and root-mean-square roughness evolved at a more stable rate with accompanying quasi-periodic ripple formation at higher etching angles (θ > 60°) and at sticking coefficient values (Sc) 0.5 ≤ Sc ≤ 1. On the other hand, smaller etching angle (θ < 60°) and lower sticking coefficient values lead to a rapid formation of wider and deeper ripples. This result of this study can be helpful to develop new surface patterning techniques by etching.
Hydraulic fracturing is a widely accepted and applied stimulation method in the unconventional oil and gas industry. With the increasing attention to unconventional reservoirs, hydraulic fracturing technologies have developed and improved more in the last few years. This study explores all applications of hydraulic fracturing methods to a great extent. It can be used as a guideline study, covering all the procedures and collected data for conventional reservoirs by considering the limited parameters of unconventional reservoirs. This paper intends to be a reference article containing all the aspects of the hydraulic fracturing method. A comprehensive study has been created by having a wide scope of examinations from the applied mechanisms to the technological materials conveyed from the different industries to utilize this technique efficiently. Furthermore, this study analyses the method, worldwide applications, advantages and disadvantages, and comparisons in different unconventional reservoirs. Various case studies that examine the challenges and pros & cons of hydraulic fracturing are included. Hydraulic fracturing is a promising stimulation technique that has been widely applied worldwide. It is challenging due to the tight and nanoporous nature, low permeability, complex geological structure, and in-situ stress field in unconventional reservoirs. Consequently, economic conditions and various parameters should be analyzed individually in each case for efficient applications. Therefore, this study provides the primary parameters and elaborate analysis of the techniques applied for a successful stimulation under SPECIFIC circumstances and provides a full spectrum of information needed for unconventional field developments. All the results are evaluated and detailed for each field case by providing the principles of applying hydraulic fracturing technologies. Many literature reviews provide different examples of hydraulic fraction methods; however, no study covers and links up both the main parameters and learnings from real cases worldwide. This study will fill this gap and illuminate the application of the hydraulic fracturing method.
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