POLYOL SYNTHESIS OF PALLADIUM HYDRIDE: BULK POWDERS VS. NANOCRYSTALS
Open Access
- Author:
- Phan, Ting-Hao
- Graduate Program:
- Chemistry
- Degree:
- Master of Science
- Document Type:
- Master Thesis
- Date of Defense:
- July 01, 2009
- Committee Members:
- Raymond Edward Schaak, Thesis Advisor/Co-Advisor
Raymond Edward Schaak, Thesis Advisor/Co-Advisor - Keywords:
- polyol synthesis
nanocrystal
palladium hydride - Abstract:
- Hydrogen is an environmentally friendly energy carrier with light weight, high energy density, and high abundance. However, the lack of suitable hydrogen storage material limits the feasibility of the technology. Recently, metal and intermetallic hydrides are considered as potential hydrogen storage materials. Therefore, development of a facile chemical method for synthesizing hydrogen storage materials is very important in this field of work. In this study, we described a polyol-based chemical route for converting Pd powders and nanocrystals into ƒÒ-PdHx using NaBH4 as hydrogen source. Different behaviors of hydrogen absorption, storage, and release between bulk and nanocrsytalline palladium were also studied. Nanocrystalline Pd absorbs hydrogen at lower temperatures than bulk Pd. Bulk palladium reacted with NaBH4 in tetraethylene glycol to form ƒÒ-PdHx completely at 190 oC, while complete conversion to ƒÒ-PdHx occurred at 120 oC for palladium nanocrystals. Also, nanocrystalline palladium reacts to form PdHx much faster at 90 oC, as well as has faster kinetics of desorbing hydrogen than bulk palladium. Well-dispersed palladium nanocrystals of about 6 to 16 nm were synthesized with ethylene glycol as reducing agent and PVP as capping agent. The general size and morphology of the Pd nanocrytals are retained after absorbing hydrogen to form ƒÒ-PdHx, as well as after releasing hydrogen to re-form Pd. Palladium powders could not convert into PdHx with bubbling H2 under otherwise identical reaction conditions. This indicates that palladium would not convert into PdHx via simply absorbing H2 gas decomposed from NaBH4, but through dissociating BH4- and then absorbing chemisorbed H atoms into its lattice.