Aluminum chloride for accelerating hydrogen generation from sodium borohydride

Abstract

Abstract The present research paper reports preliminary results about the utilization of anhydrous aluminum chloride (AlCl 3 ) for accelerating hydrogen generation through hydrolysis of aqueous solution of sodium borohydride (NaBH 4 ) at 80 °C. To the best of our knowledge, AlCl 3 has never been considered for that reaction although many transition metal salts had already been assessed. AlCl 3 reactivity was compared to those of AlCl 3 ·6H 2 O, AlF 3 , CoCl 2 , RuCl 3 and NiCl 2 . With AlCl 3 and a NaBH 4 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 AlCl 3 with CoCl2, RuCl 3 or NiCl 2 . For example, the system RuCl 3 :AlCl 3 (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 Na 2 B(OH) 4 Cl 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 AlCl 3 has a potential as accelerator for single-use NaBH 4 -based storage system.