The Surface Characteristics of Carbonaceous Materials Evaluated with T2 Distribution Analysis of Absorbed Hydrogen.

摘要

In order to develop the materials of practical significance for hydrogen storage, it is important to understand the relationships between the characteristics of materials and hydrogen storage capacities. However, with conventional adsorption measurement techniques, it is difficult to obtain the direct information about phase state of hydrogen absorbed on materials. On the other hands, 'H-NMR relaxation measurement, also called pulse NMR, is a technique for evaluating the motion and mobility of molecules in terms of the relaxation behavior of protons, nuclear spins, which are attached to the molecules. This study aim to investigate the surface characteristics of carbonaceous materials by means of !H-NMR relaxation measurement. Hydrogen was introduced on the surface of the carbons as a probe to examine the properties of the surface. The interaction between the hydrogen and surface of carbon has been evaluated with spin-spin relaxation time T2 distribution. Investigations were performed on activated carbons and Zeolite. The sample was placed into quartz high pressure NMR sample tube which was connected to a gas line and stop valve. The sample in the quartz tube was then pre-treated at 673K under vacuum (<10-5 torr) for 24hrs. After the pre-treatment, the sample in the NMR tube was moved into !H-NMR probe, then hydrogen gas of 0.5MPa-3.5MPa was introduced into the tube. The temperature of the sample was maintained with a flow of nitrogen from 133K to 303K. Spin-spin relaxation time, T2, measurements were conducted using a Tecmag Apollo Pulse NMR spectrometer operated at 38MHz for ~1H nuclei The CPMG pulse sequence was employed to generate H-NMR transverse relaxation signals. The T2 distribution was determined by taking the inverse Laplace transform of the CPMG relaxation curve performed numeric ally with the CONTIN pro gram