The structural and morphologic properties of different carbonaceous materials were studied by X-ray diffraction (XRD), Brunauer-Emmet-Teller (BET) porosimetry and transmission electron microscopy (TEM) analyses. The electrochemical behaviour of these powders used as counter electrode in dye-sensitized solar cells (DSSCs) was investigated by polarization experiments and electron impedance spectroscopy. Results were compared with DSSC using Pt as counter electrode. All DSSCs based on the carbonaceous materials showed conversion efficiencies higher than those equipped with Pt. Among the various carbon materials investigated, Acetylene Black in conjunction with graphite showed the best performance. This was interpreted from the physico-chemical analysis as due to a compromise between pores accessibility for the I 3 -reactant presents in electrolyte and appropriate surface graphiticity index of this carbonaceous material. A high degree of graphitization for the carbon black was found to enhance electron conduction and charge transfer properties.
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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