HIGH AND RAPID HYDROGEN RELEASE FROM THERMOLYSIS OF AMMONIA BORANE NEAR PEM FUEL CELL OPERATING TEMPERATURES Hyun Tae Hwang, Ahmad Al-Kukhun, and Arvind Varma School of Chemical Engineering, Purdue University 480 Stadium Mall Drive West Lafayette, IN 47907 INTRODUCTION Ammonia borane (NH 3 BH 3 , AB) has attracted considerable interest as a promising candidate material because of its high hydrogen content (19.6 wt %), hydrogen release under moderate conditions, and stability at room temperature (1). It has been reported that, at proton exchange membrane (PEM) fuel cell (FC) operating temperature in the absence of any additive, H 2 -release from solid-state AB exhibits an induction period of up to 3 hr (2-4). After hydrogen release begins, only ~1 equivalent of H 2 is obtained even with prolonged duration (>20 hr). For this reason, in prior studies reported in the literature, AB thermolysis has required temperature above 150 o C to provide 2 equivalent of hydrogen per AB (i.e. 13.1 wt % H 2 ). However, this temperature is generally too high to utilize waste heat from a PEM FC which is operated at ~85 o C, thus the thermolysis process typically requires additional heat which constitutes an energy penalty. It is known that the release of first and second mole of hydrogen from AB via thermolysis is exothermic (1, 4, 5). Thus, we expected that with effective heat management, utilizing the reaction exothermicity during the first H 2 release from AB could trigger release of second H 2 . In this study, using inert insulation material, we obtained high H 2 yield by neat AB thermolysis near PEM FC operating temperatures along with rapid kinetics, without the use of either catalyst or chemical additives. EXPERIMENTAL The experiments were conducted in a stainless steel reactor with external heating. The AB sample is placed in a small quartz vial inside the reactor, under argon environment. For effective reaction heat management, some quartz wool (4 μm diameter) was added at the top of the AB sample (~0.5 g). Starting at room temperature, with a 1 o C/min heating rate, the reaction vessel was maintained for 2 hr hold at the set point value (T SP , 90 o C). After cooling the reactor to room temperature at the end of the experiment, NH 3 was measured using Drager tube. The solid products were characterized by solid-state 11 B NMR, where the spectra were recorded using a Chemagnetics CMX400 spectrometer. The samples were run with magic angle spinning at 9 kHz. The solid products were also characterized by FT-IR spectroscopy (Thermo Scientific, Nicolet iS10). RESULTS In this work, for effective reaction heat management, some quartz wool was added at the top of the AB sample, which retains heat of exothermic thermolysis reaction while permitting product H 2 to flow. For neat AB thermolysis without quartz wool, it was observed that hydrogen gradually evolved with time after reaching 85-90 o C. After hydrogen release began, only 5 wt % H 2 yield was achieved in 90 min for this case. On the other hand, under effective heat management for the case with quartz wool, hydrogen yield ~14 wt % was achieved and stabilized quickly after sharp heat evolution (Figure 1). It was found that the sample temperature increased sharply up to ~200 o C (sufficient to release the second H 2 mole from AB), with simultaneous evolution of H 2 . These results show that the heat released during the first decomposition step can drive the second step when the reaction heat is effectively managed. Figure 1: H 2 yield and temperature profiles for neat AB thermolysis with quartz wool for T SP = 90 o C ACKNOWLEDGMENTS This work was supported by the Department of Energy, under Grant Number DOE-FG36-06GO086050 to the Purdue University Energy Center. REFERENCES 1. Hamilton, C. W.; Baker R. T.; Staubitz A.; Manners I. Chemical Society Reviews 38, 279 (2009). 2. Heldebrant D. J.; Karkamkar A.; Hess N. J.; Bowden M.; Rassat S.; Zheng F.; Rappe K.; Autrey T. Chemistry of Materials 20, 5332 (2008). 3. Himmelberger D. W.; Alden L. R.; Bluhm M. E.; Sneddon L. G. Inorganic Chemistry 48, 9883 (2009). 4. Neiner D.; Karkamkar A.; Linehan J. C.; Arey B.; Autrey T.; Kauzlarich S. M. Journal of Physical Chemistry C 113, 1098 (2009). 5. Baitalow F.; Baumann J.; Wolf G.; Jaenicke-Rossler K.; Leitner G. Thermochimca Acta 391, 159 (2002)