Formation of platinum thin films by electrochemical ALD and 2D networks of carbon nanotubes for electrochemical applications

Abstract

The main topic of this dissertation is the formation nanostructures for catalysis applications by electrochemical methods. First part of the thesis deals with the formation of Pt thin films by electrochemical atomic layer deposition method (EC-ALD). The electrochemical deposition techniques are advantageous over the vacuum phase techniques because of low cost involved and temperature (ambient) used to make thin films. However the bulk electrodeposition method doesn’t offer atomic level control to the formation of thin films. The thin films growth ends up 3 dimensional leading to rough Pt films. Hence we propose a modification in the electrodeposition technique using surface limited redox replacement method. In this method, a sacrificial layer of less noble metal such as copper is deposited on the gold substrate at under potential (UPD). The resultant monolayer of copper is replaced by Pt by flowing Pt at open circuit potential. Since UPD results in one atomic layer of copper, we expect to get one atomic layer of Pt formed by the SLRR process. Copper forms UPD on Pt as well as Au. So the SLRR process is repeated any number of times depending on the thickness of Pt film needed. Home made flow cell system is used for this study. In the second part of the thesis, we focus on fabricating carbon nanotube networks as support for catalyst materials. In order to make efficient use of carbon nanotubes as catalyst support, control on the density and defects on the carbon nanotubes need to be controlled. We propose using novel room temperature deposition method called ‘Laminar flow depoosition’ (LFD) method. In this method carbon nanotube is deposited on silane coated glass slides by coating the slides with carbon nanotube/surfactant solution and then drying in the presence of nitrogen. The amount of tubes deposited is controlled by concentration of solution and time of deposition. We show the possibility of making carbon nanotube electrodes with varying electrochemical behavior by controlling the density. Cyclic voltammetry studies show the evolution of micro or macro electrode behavior depending on the density of network. Also the amount of Pt deposition depends on the defects on the carbon nanotubes. We show that acid treatment can be used to engineer the extent of defect formation. Raman studies show the formation of defects by acid treatment. By combining the LFD and acid treatment, we are able to tailor the carbon nanotube networks.