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Study of MnOx properties using RRDE
Podal, Pavel ; Vondrák, Jiří (referee) ; Novák, Vítězslav (advisor)
This master thesis deals with qualifications of the catalytic materials for positive electrode low-temperature fuel cells. The teoretical part focuses on the physical and chemical properties of low-temperature fuel cells. There are described methods of hydrodynamic RDE and RRDE. RRDE study utilizes methods linear and cyclic voltammetry for qualifying performance of catalytic materials and presentation of results. The practical part describes the preparation various types of carbon materials. There are monitored the oxygen reduction using RRDE. Catalytic materials are evaluated: CV, stability, kinetic parameters, creation of intermediate H2O2 and kinetics of electrode reactions.
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Study of MnOx properties using RRDE
Podal, Pavel ; Vondrák, Jiří (referee) ; Novák, Vítězslav (advisor)
This master thesis deals with qualifications of the catalytic materials for positive electrode low-temperature fuel cells. The teoretical part focuses on the physical and chemical properties of low-temperature fuel cells. There are described methods of hydrodynamic RDE and RRDE. RRDE study utilizes methods linear and cyclic voltammetry for qualifying performance of catalytic materials and presentation of results. The practical part describes the preparation various types of carbon materials. There are monitored the oxygen reduction using RRDE. Catalytic materials are evaluated: CV, stability, kinetic parameters, creation of intermediate H2O2 and kinetics of electrode reactions.
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Detekce signálu v rastrovacím elektronovém mikroskopu pomocí detektorů sekundárních elektronů
Konvalina, Ivo ; Hovorka, Miloš ; Dvořáková, Marie ; Müllerová, Ilona
The collection of secondary electrons (SE) was studied for microscopes where the magnetic field penetrates to the specimen surface and for the arrangement with the specimen region free of magnetic field. Collection efficiency of secondary electron detectors varies with their energy and angular sensitivity connected with electrostatic and magnetic field distribution in the specimen region which influences the contrast of SE images. The trajectories of SE with regard to their energy, angular distributions are simulated and secondary electron detectors compared on the basis of calculated collection efficiency. For the verification of the simulated data the standard resolution-testing specimen with Au particles on a carbon substrate was used.
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Sběrová účinnost detektoru sekundárních elektronů v REM
Konvalina, Ivo ; Müllerová, Ilona
In order to collect the secondary electrons (SE), scanning electron microscopes (SEM) are equipped with the Everhart-Thornley (ET) type detector. The electrostatic field of the front grid, biased to a positive potential of several hundred volts , is to attract all SE of kinetic energy below 50 eV or at least those from the SE spectrum peak at 1(3 eV. However, the detection quantum efficiency (DQE) of such detectors has been found to be significantly lower than one, which is mainly given by their low collection efficiency. The electrostatic field of the grid cannot sufficiently penetrate toward the specimen and influence the trajectories of SE owing to grounded electrodes surrounding the specimen (specimen alone and its holder, specimen stage, pole piece of the objective lens, etc)
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