SÍNTESIS, CARACTERIZACIÓN Y EVALUACIÓN DE CATALIZADORES DE Pt/SEMICONDUCTOR/C PARA LA REACCIÓN DE REDUCCIÓN DE OXÍGENO

Abstract

The present work was oriented to study the oxygen reduction reaction (ORR) on Pt/C, Pt/TiO2/C, Pt/SnO2/C and Pt/ZnO/C electrocatalysts. The synthesis, characterization and electrochemical evaluation results is presented. The electrocatalysts were synthesized by impregnation, liquid phase photo-deposition (photolysis and photo-catalysis) and chemical vapor deposition (CVD) methods. The kinetics of platinum photo-reduction of two different Pt precursors (a) platinum acetylacetonate (C10H14O4Pt) and (b) chloroplatinic acid hexahydrate (H2PtCl6) was studied by UV-Vis spectroscopy technique. The physical properties of the synthesized materials (crystallinity, crystallite size, morphology, dispersion, thermal stability, etc.) were analyzed using X-ray diffraction, scanning and transmission electronic microscopy, XPS, Infrared spectroscopy, DTA and TGA. The electrocatalysts synthesized were electrochemical evaluated in the oxygen reduction reaction in acid medium (H2SO4 0.5M), the activity and electrochemical stability was determined by cyclic voltammetry and rotating disk electrode. Both the type of Pt precursor and preparation method had a marked influence on the physicochemical and catalytic properties. In the synthesis of Pt/C electrocatalyst, the photo-chemical reduction of Pt precursors was adjusted to a first order kinetics. The slower rate constant was obtained with the C10H14O4Pt precursor, showing the smallest particle size with a high distribution on the carbon. Pt nanoparticles between 2-10 nm were obtained depending of the preparation method and platinum precursor. Several samples of Pt-TiO2-C were prepared with different amount of TiO2 (5%, 15% y 100%) by liquid phase photo-deposition and CVD methods, the effect of the TiO2 loading on the ORR activity was evaluated. The highest activity was found with 10%Pt- 5%TiO2-C, however at increasing the amount of TiO2 a significant decrease in activity was observed. Three different catalysts 10%Pt-5%MO-C (MO=TiO2, ZnO y SnO2) were prepared by CVD and liquid phase photo-deposition for the ORR. It was observed a high activity on the Pt-TiO2-C sample independent of the synthesis method, followed by the electrocatalyst prepared with SnO2. The 10%Pt-5%TiO2-C catalyst prepared by liquid phase photo-deposition showed the best results of electrochemical activity compared with the Pt/C sample.