Adsorption of Platinum Nanoparticles on Surface Modified Open Cell-like Carbon Nanotube Structures

Abstract

Carbon nanotubes (CNTs) have extraordinary properties for applications in various potential area. CNTs have a large surface area for electrocatalyst adsorption and its own electrical properties, the CNTs are used as a supporter for electrocatalyst. In order to make more densely entangled CNTs and assemble CNTs for forming a hierarchical structure, a wetting method was used to vertically grown CNTs (V-CNTs). The capillary forces formed the open-cell like CNTs (OC-CNTs) structures. The V-CNTs were synthesized by using LP-TCVD with 24um in height and OC-CNTs structures were formed with around 5um in height from as-grown V-CNTs by capillary forces. The height of OC-CNTs was reduced from the height of pristine V-CNTs and there are no any chemical damages on OC-CNTs as proven with a similar D/G band ratio (0.71) of OC-CNTs and V-CNTs. In order to functionalize the surface of OC-CNTs for generating the amino terminated groups, the NH3 plasma treatment was performed in a plasma-enhanced CVD chamber. The amine-functional groups were acted as anchoring sites for Pt catalyst adsorption. The functional groups were confirmed by X-ray photoelectron spectroscopy (XPS). In this thesis, the optimum conditions of OC-CNTs formation were investigated and the adsorption process of Pt catalysts was also optimized. The amine-functionalized OC-CNTs on Si substrates were successfully modified with Pt particles by immersing in the Pt precursor solution (H2PtCl6) followed by a reduction process by a reducing agent (NaBH4). By changing the concentration of Pt precursor and reducing agent, the size and distribution degree of Pt nanoparticles were controlled. The characterizations of adsorbed Pt nanoparticles was confirmed by scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction spectroscopy (XRD) and XPS. The morphology of Pt nanoparticles was investigated depending on the concentration of the reducing agent. The elemental analysis showed the presence of Pt nanoparticles and XRD analysis indicated the crystal structures of Pt nanoparticles and SEM showed the average size of adsorbed particles. While XPS analysis proved the presence of the metal Pt(0) and oxide Pt(II) and Pt(IV), these results proved that Pt nanoparticles were successfully generated from Pt ions by reduction and adsorbed on the surface of OC-CNTs. Taken together, these experimental results clearly suggest that the adsorption method of Pt nanoparticles on modified CNTs surface is potentially significant to form a catalyst layer.