Aluminum chloride for accelerating hydrogen generation from sodium borohydride

The present research paper reports preliminary results about the utilization of anhydrous aluminum chloride (AlCl₃) for accelerating hydrogen generation through hydrolysis of aqueous solution of sodium borohydride (NaBH₄) at 80 °C. To the best of our knowledge, AlCl₃ has never been considered for that reaction although many transition metal salts had already been assessed. AlCl₃ reactivity was compared to those of AlCl₃·6H₂O, AlF₃, CoCl₂, RuCl₃ and NiCl₂. With AlCl₃ and a NaBH₄ solution having a gravimetric hydrogen storage capacity (GHSC) of 2.9 wt.%, almost 100% hydrogen was generated in few seconds, i.e., with a hydrogen generation rate (HGR) of 354 L min⁻¹ g⁻¹(Al). This HGR is one of the highest rates ever reported. Higher HGRs were obtained by mixing AlCl₃ with CoCl2, RuCl₃ or NiCl₂. For example, the system RuCl₃:AlCl₃ (50:50 mass proportion) showed a HGR > 1000 L min⁻¹ g⁻¹(Ru:Al). The hydrolysis by-products (once dried) were identified (by XRD, IR and elemental analysis) as being Al(OH)₃, NaCl and Na₂B(OH)₄Cl and it was observed that even in situ formed Al(OH)₃ has catalytic abilities with HGRs of 5 L min⁻¹ g⁻¹(Al). All of these preliminary results are discussed, which concludes that AlCl₃ has a potential as accelerator for single-use NaBH₄-based storage system.