Synthesis,characterization and hydrogen sorption studies of mixed sodium‐potassium alanate

The aim of the present investigation is to synthesize mixed sodium potassium alanate (K₂NaAlH₆) and to explore its hydrogen sorption characteristics. K₂NaAlH₆ is synthesized through ball milling of KH and NaAlH₄ in the molar ratio 2:1 under hydrogen pressure of 10 bar. The temperature programmed desorption experiment shows that the synthesized K₂NaAlH₆ has peak desorption temperature of ～352°C and reveals appreciable rehydrogenation kinetics under 6 bar hydrogen pressure at 300°C. The investigations are also focused on the catalytic effect of carbon nanostructures (CNS) namely, the graphene sheet (GS) and single wall carbon nanotube (SWCNT) and titanium halides (TiCl₃ and TiF₃) on K₂NaAlH₆. In the case of graphene and SWCNT catalyzed K₂NaAlH₆, the peak desorption temperature gets reduced to ～347°C and ～341°C respectively. The catalytic effects of CNS and titanium halide on K₂NaAlH₆ are also compared in the investigation. Between the two types of catalysts, halides are found to be better than CNS and out of the two halides, TiF₃ is found to be the best catalyst for hydrogen sorption in K₂NaAlH₆. The peak desorption temperature decreases significantly from 352°C to ～324°C for TiF₃ catalyzed K₂NaAlH₆. Thus, the desorption activation energy reduces drastically from 124.43 kJ/mol (synthesized K₂NaAlH₆) to 88.05 kJ/mol for TiF₃ catalyzed K₂NaAlH₆.