Enhanced hydrogen storage property of MgH2 caused by a BaCrO4 nanocatalyst

Abstract

Magnesium hydroxide (MgH₂) has a broad application prospect in solid hydrogen storage, but the associated higher dehydrogenation temperature and undesirable cycling capacity limit its large-scale application. In this study, a BaCrO₄ nanocatalyst prepared via a wet chemistry method was added to MgH₂ to achieve better kinetic and thermodynamic performances. Kinetic tests suggested that the onset hydrogen desorption temperature was decreased for milled MgH₂ from 390 °C to below 280 °C after the introduction of a 5 wt% BaCrO₄ nanocatalyst and the maximum dehydrogenation amount was up to 6.32 wt%. With regard to hydrogen absorption, MgH₂ incorporated with 10 wt% BaCrO₄ could fully absorb 5.78 wt% H₂ within 10 min at 300 °C and recharge 3.1 wt% H₂ at a low temperature of 250 °C. In comparison, the hydrogen uptake amounts for MgH₂ under the same conditions were only 3.98 wt% and 1.52 wt%. With regard to hydrogen desorption, 5 wt% BaCrO₄-modified MgH₂ could discharge 4.25 wt% H₂ within 10 min at 325 °C and 4.81 wt% H₂ at 300 °C, while MgH₂ could not dehydrogenate at 300 °C. Meanwhile, only 5% of the performance decayed for 5 wt% BaCrO₄-modified MgH₂ during ten cycles. Dehydrogenation E_a reduced to 106.75 kJ mol⁻¹ in contrast to 156.55 kJ mol⁻¹ for MgH₂. In addition, DFT results verified that the BaCrO₄ nanocatalyst reduced the band gap from 2.78 eV to 2.16 eV to improve the thermodynamic property of MgH₂ and contributed to the decrease in the dehydrogenation energy barrier from 2.27 eV to 1.54 eV. This work provides an insight into the performance of ternary transition metal nanocatalysts for MgH₂ hydrogen storage systems.