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.