Investigation and characterization of Pt-modified Au catalysts and polymer composites by electrochemistry, Raman and surface enhanced Raman spectroscopy (SERS)

This dissertation thesis consists of six chapters. The main focus of this study is the need for understanding the reaction mechanism and intermediates formed on Pt-modified Au surface as anode catalysts in the formic acid fuel cells. Chapter 1 gives an introduction to formic acid and methanol fuel cells, an overview of the current catalysts employed at the anode of the fuel cells, specifically the Pt-modified Au electrodes as potential catalysts and the different deposition methods for preparing this catalytic surface. Information about different electrochemical methods used like cyclic voltammetry and potential step method along with other characterization methods and spectroscopic techniques has also been given. As one of the main methods to characterize the catalysts, Raman and surface enhanced Raman spectroscopy have been discussed in detail. The electrooxidation of formic acid and the nature of the intermediates at a platinum-modified gold surface prepared through spontaneous deposition were characterized using a combination of electrochemistry and in situ surface enhanced Raman spectroscopy (SERS). Spontaneously deposited platinum on gold showed unique high catalytic activity for formic acid electrooxidation. The oxidation current of formic acid is more than five times higher on the Pt-modified gold electrode surface than on a bare Pt surface and about 72 times higher than on a bare Au surface. SERS results reveal the involvement of a novel HCOO− adsorbate at 300 cm−1. Both electrochemical and spectroscopic results suggest that the formic acid electrooxidation takes place by the dehydrogenation pathway involving a low frequency formate intermediate on the Pt-modified gold electrode catalyst. Next, the effect of the deposition solution employed in the spontaneous deposition process was explored and demonstrated to play an important role in catalytic activity of these surfaces. Electrochemical studies show that Pt-modified Au surfaces prepared from bromoplatinate solution are most active in oxidizing formic acid. The second most active surface for formic acid electrooxidation was that from chloroplatinate followed by that from the iodoplatinate solutions. Also, the optimal condition to prepare the most active surface is different for various haloplatinate solutions. In situ surface enhanced Raman spectroscopy (SERS) with potential control revealed the presence of formate at 300 cm-1 as the reaction intermediate in the catalytic processes on all three Pt-modified Au surfaces, but with different potential-dependent behaviors. A clear and transparent bis ethylenedioxy tetrathiafulvalene iodine doped polymer films (BEDO-TTF) was successfully prepared by electrochemical method of cyclic voltammetry. The formation of the transparent films has been linked to the reduction of the iodine species in the film to iodide species giving rise to colorless films. Furthermore, Raman studies have revealed the presence of different iodide species like triodide, pentaiodide and iodine when anodic and cathodic potentials were applied to the films. Also, it was seen that the iodine was complexed with the BEDO-TTF polymer in a stoichiometry of 2.4: 3 [(BEDO-TTF) 2.4I3] at certain concentration in the doping technique. Raman studies were also conducted on single walled carbon nanotubes (SWCNTs) to study the defects introduced during the ball milling procedure and Ru doping. The Raman results reveal that both ball milling procedure and Ru doping leads to the formation of more defects and carbonaceous species in the SWCNTs. Thus, both electrochemical and Raman method were demonstrated to characterize the composition and properties of various materials including conducting polymer and carbon nanotube