Year

2011

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

1. Synthesis of two kinds of Pt-M alloy (Pt-Ni and Pt-Co) through the chemical reduction method - Electrochemical testing and physical characterization of as-prepared catalysts have also been conducted. Although these PtxNi and Pt1 xCox alloy catalysts contain a reduced content of Pt, they exhibit significantly enhanced catalytic activity towards oxygen reduction compared to pure platinum catalyst.

2. Synthesis of two kinds of special core-shell structure catalyst materials – Structural characterization to confirm the special structure was carried out. And electrochemical tests show that although the Cocore-Ptshell particles have a much reduced content of Pt, they exhibit significantly enhanced catalytic activity toward oxygen reduction as compared to pure Pt catalyst,

3. Acid treatments to improve the surface properties of carbon – The results show that the Pt nanocatalysts exhibited enhanced activity in the oxygen reduction reaction (ORR) on the activated carbon compared to the pristine carbon black.

4. CNTs and graphite as catalyst supports - 20wt% Pt/C catalysts with Vulcan XC-72 (BASF), pristine double-walled carbon nanotubes (DWCNTs), and activated double-walled carbon nanotubes as the carbon sources, are investigated. The results show that the Pt nanocatalysts exhibited enhanced electrochemically active surface areas and improved activity in the oxygen reduction reaction (orr) on the activated DWCNTs compared to the pristine DWCNTs or the Vulcan XC-72. Also, I have found that the use of graphene can be promising in effectively reducing the carbon corrosion problem.

II. Hydrogen storage on Carbon-Based Adsorbents

Hydrogen has emerged as one of the most promising candidates for the replacement of current carbon-based energy services because of its zero CO2 emission. Storage is one of the key issues for the realization of fuel-cell powered vehicles using hydrogen as the energy carrier. However, how to store hydrogen easily and cheaply is still a big problem. As research on hydrogen storage is an important subject, and carbon nanotubes are new materials for hydrogen storage, I have carried out the hydrogen storage properties of CNTs.

The achievements are as follows:

1. Hydrogen storage properties of double-walled carbon nanotubes (DWCNTs) at ambient temperature - Using Pd catalyst for dissociation of H2 into atomic hydrogen and KOH activation for formation of defects on DWCNT surface, the defect sites on DWCNTs as adsorption sites of atomic hydrogen were created by chemical activation using KOH. Pd nanoparticles loaded on DWCNT surfaces for dissociation of H2 into atomic hydrogen, which spills over to the defect sites on the DWCNTs. Both led directly to enhanced hydrogen storage compared to that on pristine carbon nanotubes. So I found that the hydrogen storage capacity can be enhanced by chemical activation and loading with Pd nanoparticles.

2. Effects of different reductants for palladium loading on the hydrogen sorption characteristics of double-walled carbon nanotubes (DWCNTs) – Pd nanoparticles were loaded on DWCNT surfaces for dissociation of H2 into atomic hydrogen, which spills over to the defect sites on the DWCNTs. When using different reductants, the reduction capabilities and other effects of the different reductants are different, which affect the hydrogen storage capacity of the DWCNTs. I have found that the hydrogen storage capacity can be enhanced by loading with 2% Pd nanoparticles and selecting a suitable reductant.

Furthermore, the sorption can be attributed to the chemical reaction between atomic hydrogen and the dangling bonds of the DWCNTs.

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