Environmental Engineering Reference
In-Depth Information
Fig. 6 Mg/polymer composite hydrogen storage material. Here Mg nanoparticles are encapsu-
lated in PMMA, a gas-permeable polymer. Reproduced with permission from Jeon 2011
TPD methods are employable without an apparatus specifically built for hydro-
genation/dehydrogenation purposes. Also, the data analysis is more flexible than
that of the isothermal methods, i.e., PCI and GCI.
3.1 Non-isothermal Methods
When using TGA or DSC, the hydrogen desorption kinetics of different materials
can be qualitatively characterized by comparing the initial onset of transformation
in the materials. For example, in TGA, a characteristic plot of weight percent
versus temperature (Fig.
7
)[
72
] displays an onset of weight loss, corresponding to
loss of hydrogen at different temperatures, for an assortment of materials. This
onset can be observed at lower temperature for the various catalyzed materials
than for that of the non-catalyzed MgH
2
. Similarly in DSC, where a quantitative
endotherm or exotherm signifies a phase change as different temperatures are
scanned, it can be seen that hydrogen desorption for the nickel-catalyzed sample
occurs at a much lower temperature with respect to that of the non-catalyzed
sample (Fig.
8
)[
40
].
For the purposes of hydrogen storage, the better performing material will
exhibit an onset of desorption at a lower temperature. However, due to the vari-
ation within experimental procedure and instrument calibration, if the performance
of a material is to be compared to that of the other literature, an activation energy
for desorption should be determined. The activation energy can be calculated by
analyzing TGA and DSC data with one of the two following equations:
Search WWH ::
Custom Search