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.