CATALYTIC ASPECTS OF NON-NOBLE METALS ON HYDROGEN GENERATION FROM HYDROLYSIS OF SODIUM BOROHYDRIDE

Open Access
Author:
Park, Sunyoung
Graduate Program:
Materials Science and Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
June 25, 2008
Committee Members:
  • Mirna Urquidi Macdonald, Thesis Advisor
  • Melik C Demirel, Thesis Advisor
Keywords:
  • Hydrogen
  • Sodium Borohydride
  • Catalyst
  • Co-PPX
  • Cobalt
  • Aluminum
Abstract:
In the generation of hydrogen from chemical hydrides, the catalyst is a key component. The use of expensive metals as catalysts limits the feasibility of the technology. Therefore, development of inexpensive and effective catalysts is very important in this field of study. In this work, cobalt based and aluminum alloy based catalysts for hydrogen generation from hydrolysis of alkaline stabilized sodium borohydride solutions were studied. For the cobalt catalyst study, nanoporous cobalt thin films were fabricated by metallization of nanostructured poly(chloro-p-xylylene). The hydrogen generation performance of the cobalt PPX-Cl nano thin films (NTFs) was evaluated. Due to the high porosity of the nanostructure of the films, excellent hydrogen generation rates, which are comparable with novel metals, were achieved. Cobalt powder (1.6¥ìm dia.) was tested as a catalyst. It was postulated that passive film and re-precipitated film were formed on the cobalt catalyst in alkaline stabilized sodium borohydride solutions. To study the effect of the oxide films on the catalytic activity of the cobalt, ethylenediaminetetra acid (EDTA) was added to the electrolyte and hydrogen generation rates were measured. It was expected that EDTA would effectively suppress the cobalt oxide formation, increasing the hydrogen generation rate. However, the results showed that the hydrogen generation was decreased in the solutions with EDTA. In deaerated solutions, the hydrogen generation rates were increased regardless of the addition of EDTA. These results are explained as a blockage of Co-EDTA chelate, which decreases the absorption of species. Evaluation of an aluminum alloy as a catalyst was carried out as a catalyst for sodium borohydride hydrolysis. The effects of EDTA and deaeration were also investigated. The results were opposite to that of cobalt. EDTA effectively increased the hydrogen generation rates, while deaeration had no effect on the hydrogen generation rates. Hydrogen was generated by both hydrolysis of NaBH4 and the dissolution of aluminum in alkaline solutions.