Electrochemistry, Electrocatalysis and Materials Science of Bulk Pt and Nanoscopic Pt, PtNi, PtCo, and Ni(OH)2 Materials: Preparation, Characterization, Catalytic Activity and Corrosion Behaviour
Research on the degradation of platinum (Pt) and nickel (Ni) materials is of high importance to the fuel cell and electrolyser technologies, because their degradation translates into irreversible materials loss and deterioration of these energy systems’ performance. Polycrystalline platinum (Pt(poly)) serves as a model system, and experimental studies using Pt(poly) create important background knowledge that will facilitate the identification and quantification of phenomena unique to the nanoscopic Pt-based electrocatalysts. In the thesis, I present original results on the preparation, characterization, catalytic activity and corrosion behaviour of bulk Pt and nanoscopic Pt, PtNi, PtCo and Ni(OH)2 materials. I studied the electrochemical and corrosion behaviour of Pt(poly) in acidic media saturated with N2(g), O2(g) or H2(g). I analyzed the influence of the potential scan rate (s) (1.00–50.0 mV s−1 range) on the cyclic-voltammetry (CV) behaviour of Pt(poly). The results indicated that the Pt surface oxide reveals catalytic duality and acts both as an inhibitor and a catalyst in the oxygen reduction and hydrogen oxidation reactions (ORR and HOR). I also analyzed the influence of the value of s (0.10–1.00 mV s−1 range) on the polarization behaviour of Pt(poly) in anodic and cathodic directions. The results demonstrated that the corrosion data obtained at s = 0.10 mV s−1 are the most representative of the corrosion of Pt(poly). I employed a similar methodology to study the electrochemical and corrosion behaviour of the Pt-base nanocatalysts. Nanocatalysts were synthesized using the “water-in-oil” microemulsion method. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to examine their average size, shape, and size distribution; they were determined to be spherical with a fine average size and a narrow size distribution. Thermo-gravimetric analysis (TGA) measurements were carried out to evaluate the metal loading, which was very close to the predetermined target values. Surface oxide formation and reduction were examined using in-situ confocal Raman spectroscopy. A comparison of the corrosion data (obtained by performing polarization experiments) demonstrated that nanocatalysts do not corrode in the presence of H2(g), corrode slightly in the presence of N2(g), and corrode severely in the presence of O2(g).
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