aIn real catalyst systems, it is difficult to establish a correlation between catalytic properties and the shape (crystal planes, corners and steps) of the active catalytic particles. In this paper we present a clear shape dependence of the catalytic properties of a Vulcan-supported fuel cell catalyst having 4 nm cubo-octahedral platinum(0) nanocrystallites with (111) and (100) surfaces stabilized by sodium polyacrylate. The electrode materials were characterized by CO-stripping cyclic voltammetry and transmission electron microscopy (TEM), showing that no agglomeration had occurred among the nanoparticles on the catalyst surfaces.
The title redox couple, in noncoordinating perchlorate medium, has been used to probe the electrochemical behavior of different IrO2-based electrodes; pure oxide electrodes, as well as IrO2-SnO2 mixtures, have been investigated. The obtained results show that the electrode material strongly affects the electrochemical response. A tentative explanation, based on the different point of zero charge of the considered oxides, is presented.
Oxygen-depolarized cathodes consisting of gas-diffusion electrodes (GDEs) for electrolysis in a chlor-alkali cell at 90°C were studied. The electrode design was based on a carbon-free catalyst and comprised of a mixture of micronized silver particles, a small amount of Hg and PTFE binder. The cathodes were investigated by electrochemical measurements, and surface and morphological analyses before and after different operation times in chlor-alkali cells. Electrode stability was investigated by life-time tests. The surface properties of gas diffusion electrodes were studied for both fresh and used cathodes by X-ray photoelectron spectroscopy (XPS). Transmission (TEM) and scanning electron microscopy (SEM-EDX) were used to investigate morphology. The bulk of gas diffusion electrodes was studied by X-ray diffraction (XRD) and thermogravimetric analysis (TG-DSC). At least two main degradation processes that occur on different time-scales were identified and attributed to segregation and loss of the second metal at the interface and a decrease in the hydrophilic properties with time. Furthermore, an increase in the precipitation of compounds from the reaction process also decreased performance by the occlusion of reaction pores.
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