Ehab N. El Sawy

Nano-porous iridium and iridium oxide thin films formed by high efficiency electrodeposition

The goal of this work has been to fabricate very thin, highly porous Ir films, of use in a wide variety of applications. To achieve this objective, Ir was electrodeposited on a Au-coated quartz crystal, allowing in situ mass measurements to be carried out while concurrently monitoring the charge passed, as a function of the deposition potential, H2IrCl6 concentration, and time. Ir thin films (<5 nm) could be deposited at 100% charge efficiency at an optimum potential of 0.1–0.2 V vs. RHE, all in room temperature 0.5 M H2SO4 containing various concentrations of H2IrCl6. Field emission scanning electron microscopy and in situ surface area measurements showed that the Ir films are uniform and yet highly porous (up to 50%), independent of film thickness. We were also able to efficiently convert the electrodeposited Ir to Ir oxide, without significant loss of metal or diminished coating adhesion, while also maintaining their very high surface area properties. These interesting thin films are very promising for a wide variety of electrocatalytic and sensing applications.

Corrosion behaviour of pure Mg, AS31 and AZ91 in buffered and unbuffered sulphate and chloride solutions

Abstract The low corrosion resistance of magnesium limited its application in industrial affairs. The main corrosive anions for magnesium are sulphate and chloride. This paper deals with their effect at low concentrations on the corrosion behaviour of Mg and Mg based alloy (AS31 and AZ91) in presence/absence of buffer solutions (pH 8). The electrochemical measurements used are open circuit potential and potentiodynamic polarisation. The results exposed that in the absence of a protective layer, general corrosion is observed to occur at greater rate than when sulphate is present; however, the general corrosion is transformed to localised corrosion faster in presence of chloride. In the presence of a protective layer, the localised corrosion is perceived in the case of chloride more than sulphate. The presence of aluminium in the alloys has two contradictory actions. One increases the passivity of the formed layer and the other increases the localised corrosion. The percentage of aluminium in the alloy controls these actions.The low corrosion resistance of magnesium limited its application in industrial affairs. The main corrosive anions for magnesium are sulphate and chloride. This paper deals with their effect at low concentrations on the corrosion behaviour of Mg and Mg based alloy (AS31 and AZ91) in presence/absence of buffer solutions (pH 8). The electrochemical measurements used are open circuit potential and potentiodynamic polarisation. The results exposed that in the absence of a protective layer, general corrosion is observed to occur at greater rate than when sulphate is present; however, the general corrosion is transformed to localised corrosion faster in presence of chloride. In the presence of a protective layer, the localised corrosion is perceived in the case of chloride more than sulphate. The presence of aluminium in the alloys has two contradictory actions. One increases the passivity of the formed layer and the other increases the localised corrosion. The percentage of aluminium in the alloy controls thes...

Nanoengineered Ircore@Ptshell Nanoparticles with Controlled Pt Shell Coverages for Direct Methanol Electro-Oxidation

The design and application of bimetallic alloy nanoparticles (NPs) for electrocatalytic applications are challenged by the need to clearly identify and understand the individual effect of each component. In the present work, the focus has been on PtIr NPs, with alloyed NPs being previously shown to be active toward the methanol oxidation reaction (MOR), but for which the mode of action of the Ir component remains uncertain. We have therefore nanoengineered a family of Ircore@Ptshell NPs, using a modified polyol method, to control the Pt shell coverage (up to 2 monolayers) and thus to allow the separation of the bifunctional and electronic effects of Ir on the Pt activity. It is shown that the Ir core size and crystallinity do not change with the deposition of the Pt shell, as confirmed by transmission electron microscopy and X-ray diffraction. CO stripping and hydrogen underpotential deposition/removal were used for the first time to determine the surface composition of the Ircore@Ptshell NPs. It is shown that the Ircore enhances the MOR activity of the Ptshell primarily through the bifunctional effect, with an optimum Pt coverage of 0.4 of a monolayer. At 60 °C, an additional electronic effect of Ir on Pt can be discerned, causing an inhibition in the MOR rate by weakening the adsorption of methanol on the Ptshell, thus helping to remove the adsorbed CO intermediate from the shell surface.

PtxIry alloy nanoparticles with fully tunable bulk and surface compositions

PtxIry nanoparticles (NPs) are of great interest, largely due to their wide range of applications in gas phase catalysis, electrocatalysis, sensors, and more. Most of the prior work on PtxIry NPs, formed using a variety of approaches, has shown that the surface becomes uncontrollably enriched with Pt relative to the NP bulk. In this work, PtxIry alloy NPs (with x and y (35–85%) being the atomic percent of Pt and Ir, respectively) were synthesized using the simple polyol method, using Pt and Ir solution precursors and employing two sequential heating steps. It is shown that this method prevents the enrichment of the surface with either Pt or Ir, resulting in the same surface and bulk compositions, fully controllable by modifying the ratio of metal precursors in solution. This was confirmed by electrochemical studies, wavelength dispersive X-ray spectroscopy (XRD), and energy dispersive X-ray spectroscopy (EDS) coupled with high resolution transmission electron microscopy (HRTEM), while XRD analysis confirmed PtxIry alloy formation. The predictable and tunable composition of these materials, both in the NP bulk and at their surfaces, is a novel and important advantage for their future use as catalysts and reagents for a broad range of reactions, including methanol oxidation, as demonstrated here.

Electrochemical Energy Production Using Fuel Cell Technologies

Fuel cells are highly efficient and environmentally friendly energy conversion devices that are receiving increasing attention and are steadily moving toward commercialization. Fuel cells deliver electricity and heat, based on the spontaneous electrochemical oxidation of fuels at the anode and the reduction of oxygen at the cathode, without combustion. In many ways, fuel cells are similar to batteries, although they do not require recharging and operate as long as fuel continues to be provided. There are four leading types of fuels reviewed in this chapter, proton exchange membrane fuel cells (PEMFCs) operating on clean hydrogen, direct alcohol (primarily methanol) fuel cells (DAFCs), solid oxide fuel cells (SOFCs), and molten carbonate fuel cells (MCFCs). PEMFCs and DAFCs normally operate at below 100 °C and are targeted primarily for transportation and mobile applications, while SOFCs and MCFCs, which run at temperatures above 600 °C, can run on a wide variety of fuels and are intended mostly for stationary combined heat and power applications. This review is focused primarily on a description of each of these technologies, with an emphasis on the materials used in the electrodes, the electrolyte that separates them, and the current collectors.