(218a) Ammonia Borane Dehydrogenation Always Generates Ammonia, How Much and How to Remove It?

Hydrogen is a widely acknowledged clean fuel for PEM fuel cell (FC) vehicles and, Ammonia Borane (AB) is among the best hydrogen storage materials as it contains 19.6 wt.% and 150 kg/m3 H2 on weight and volume basis, respectively. Current methods to release hydrogen from AB include catalytic hydrolysis, thermolysis and hydrothermolysis [1]. As recently shown experimentally [2], all of these methods generate ammonia gas as a by-product of ammonia borane dehydrogenation. In addition to poisoning the anode catalyst site of PEM FC, ammonia can also cause ion exchange with protons in the polymer electrolyte. It has been reported that as low as 13 ppm NH3 can significantly decrease the FC performance, and that the degradation is irreversible for long-term exposure (15 hr) to 30 ppm NH3 [3]. Thus, to utilize any AB-based method to generate hydrogen for PEM FC applications, a technique for removing ammonia from the product gas stream is required.

In this study, for different operating conditions, we first quantified the ammonia generated from the more promising thermolysis and hydrothermolysis methods. Next, we evaluated different methods for ammonia removal, including membranes, absorption, adsorption, selective oxidation and cracking. The results show that, using a combination of these methods, ammonia can be removed completely. The optimized system configuration for ammonia removal was achieved to minimize the weight penalty of the added system.

[1] Diwan M., Hwang H. T., Al-Kukhun A., Varma A., ?Hydrogen Generation from Noncatalytic Hydrothermolysis of Ammonia Borane for Vehicle Applications,? AIChE Journal (in press, DOI 10.1002/aic.12240). 2010

[2] Hwang H. T, Al-Kukhun A., Varma A., ?Hydrogen for Vehicle Applications from Hydrothermolysis of Ammonia Borane: Hydrogen Yield, Thermal Characteristics, and Ammonia Formation,? Ind. Eng. Chem. Research (in review, 2010).

[3] Halseid, R., Vie, P. J. S., Tunold, R., ?Effect of Ammonia on the Performance of Polymer Electrolyte Membrane Fuel Cells?. J Power Sources 2006, 154: 343.