Silanol-Enhanced Dehydrogenation of Ammonia Borane with Silicic Acid Catalyst

Abstract

Ammonia borane (AB), with a 19.6-wt% H₂ content, is a promising hydrogen storage material for polymer electrolyte membrane fuel cells (PEMFC). However, traditional thermal decomposition of boric acid generates ammonia, which is detrimental to fuel cells. This study explores the use of silicic acid (SA) as a catalyst for AB, yielding 12.0 wt% of H₂ at approximately 100 °C, making it suitable for fuel-cell operation. Notably, when the AB mass ratio is increased to 90 wt%, the reaction temperature increases slightly, yet it produces up to 12.3 wt% of H₂. Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analyses confirm that SA contains more silanol groups than SiO₂. Pyridine infrared analysis reveals that SA has a higher distribution of Lewis acid sites, which play a vital role in the dehydrogenation of AB. In addition, when in-situ mass spectrometry analysis is performed, ammonia is not detected, indicating that no filtration is required for fuel-cell applications. In conclusion, this study demonstrates that SA enhances the dehydrogenation of AB at low temperatures, achieving a high H₂ yield without ammonia production. This makes SA a promising catalyst for efficient and safe H₂ storage in fuel cells, with potential applications in mobile and aerial vehicles.