Fast hydrogenation and dehydrogenation of Pt/Pd bimetal decorated over nano structured Ag islands grown on rough alumina substrate

Abstract

In this thesis, the author developed and analyzed the fabrication and characterization of the hydrogenation and dehydrogenation in Pt/Pd bimetal decorated over Ag nanoislands grown over alumina substrate. The Ag nanoislands development on alumina substrate, formation of uniform Pt/Pd bimetal and their gas absorbing and desorbing performance along with theoretical investigations at various conditions such as different gas concentrations, different temperature have been undertaken. A thermally annealed surface diffusion effects on the morphology of Ag nanoislands were analyzed with different morphological conditions. The author explored the catalytic bimetal nano structural effects on the surface charge density and the interfacial interactions with well-shaped Ag metal nanoislands. Several materials characterizations such as x-ray diffractions, atomic force microscopy, scanning electron microscopy, EDS analysis, photoluminescence effects, x-ray photo spectroscopy along with bimetals computational simulation were employed to confirm the catalytic properties of the as prepared structure toward hydrogen gas. The morphology of Ag nanoislands was optimized by RF magnetron sputtering and rapid thermal annealing process. Later, Pt/Pd bimetal (10/10) nm were deposited by RF magnetron sputtering on the nanostructured Ag islands. After the surface morphological optimization of Ag nanoislands, the resultant structure Pt/Pd@Ag nanoislands at alumina showed a fast and enhanced hydrogenation and dehydrogenation (20/25 sec), response magnitude of 2.3% (10000 ppm), and a broad detection range of 500 ppm to 40000 ppm at the operating temperature of 120˚C. The superior hydrogenation and dehydrogenation features can be attributed to the hydrogen induced changes in the work function of Pt/Pd bimetal which enhances the columb scattering of percolated Pt/Pd@Ag nanoislands. More importantly, the atomic arrangements and synergetic effects of complex metal alloy interfacial structure on Ag nanoisland, supported by rough alumina substrate incorporates vital role in accelerating the H2 absorption and desorption properties. For the future hydrogenation and dehydrogenation related applications, this research provides a new technique to explore by using the simple nanostructure based model.