Deciphering decomposition pathways in Na2CrO4-catalysed Mg(AlH4)2 and Mg(BH4)2 systems

This study explores the catalytic effect of Na2CrO4 on the hydrogen storage performance of Mg(AlH4)2 and Mg(BH4)2. For Mg(AlH4)2, Na2CrO4 incorporation significantly enhances dehydrogenation characteristics. The hydrogen desorption temperatures decrease from 178.4°C and 291.6°C to 170.4°C and 279°C, respectively, while the activation energy reduces from 114.4 ± 8.3 to 103.9 ± 2.5 kJ/mol, indicating improved kinetics. Structural investigations reveal that the catalyst remains stable and facilitates the decomposition pathway involving MgH2 and Mg2Al3 formation without altering the fundamental reaction mechanism. In contrast, Mg(BH4)2 exhibits a different catalytic response. Although the activation energy remains nearly unchanged, Na2CrO4 modifies the hydrogen desorption profile by transforming the multi-step plateau behaviour into a more continuous release pattern. C-Mg(BH4)2 desorbed hydrogen rapidly near 300°C, with a total absolute amount of hydrogen release (with respect to active mass of Mg(BH4)2 only) ∼13.8 wt.%. Phase analysis confirms the transformation from α to β-Mg(BH4)2 followed by the formation of MgB2 and Mg, while the catalyst remains structurally intact. X-ray photoelectron spectroscopy study also strengthens the mechanism described for both alanate and borohydride systems based on X-ray diffraction and infrared.