SPEAKER:	Bing-Hung Chen Department of Chemical Engineering National Cheng Kung University, Taiwan
TITLE:	Introduction to Chemical Hydrides as Hydrogen Storage Materials
DATE:	March 24 2011
TIME:	10:30 am
PLACE:	JHE 326H

ABSTRACT

Proton-exchange-membrane fuel cells based on hydrogen have attracted much attention, because of their higher energy efficiency and recognition as one of the emerging technologies in green power generation. However, there are still some challenges faced in realization of hydrogen economics. One of the problems to be resolved is on the mode of hydrogen storage and supply to PEMFC. Among various hydrogen storage modes, chemical hydrides are considered as probably the best candidate to do this job. In this work, we will give a brief but general introduction to chemical hydrides as hydrogen storage materials and, certainly, discuss on the regeneration methods of the spent chemical hydrides. Sodium borohydride and ammonia borane (AB) will be used as the example for elucidation. A convenient method was developed to regenerate spent sodium borohydride (NaBH4) and ammonia borane (NH3BH3), which were confirmed mainly as sodium metaborate (NaBO2) and boric acid (H3BO3) with various techniques, back to pristine NaBH4 and subsequently, ammonia borane. Two different regeneration schemes, i.e. the mechanochemical reaction of NaBO2 with MgH2 through planetary ball milling at room temperature and conventional wet chemical reactions, have been attempted and will be demosntrated. The samples were characterized by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) spectroscopy. In order to improve the production yield of NaBH4 from NaBO2 via mechanochemical reaction, it was necessary to add MgH2 initially in stoichiometric excess. When MgH2 in 20 mol% excess was initially added, yield of sodium borohydride was found to reach 75.3%.