Dual-tuning of de/hydrogenation kinetic properties of Mg-based hydrogen storage alloy by building a Ni-/Co-multi-platform collaborative system

The Mg-based hydrogen storage alloy with multiple platforms is successfully prepared by ball milling Co powder and Mg-RE-Ni precursor alloy, and its hydrogen storage behavior was investigated in detail by XRD , EDS , TEM, PCI , and DSC methods. The ball-milled alloy consists of the main phase Mg, the catalytic phases Mg 2 Ni, Mg 2 Co as well as a small amount of Mg 12 Ce, and convert into the MgH 2 –CeH 2.73 -Mg 2 NiH 4 –Mg 2 CoH 5 composite after hydrogenation. The composite has three PCI platforms corresponding to the reversible de/hydrogenation reaction of Mg/MgH 2 , Mg 2 Ni/Mg 2 NiH 4 and Mg 6 Co 2 H 11 /Mg 2 CoH 5 . Among them, the transformation between Mg 2 Ni and Mg 2 NiH 4 triggers the “spill-over” effect which promote the decomposition of MgH 2 phases and enhances the hydrogen desorption kinetics. Meanwhile, the conversion of the Mg 6 Co 2 H 11 to Mg 2 CoH 5 phase induces the “chain reaction” effect, which leads to preferential nucleation of Mg phase and improves the hydrogen absorption kinetics. Therefore, the Mg-RE-Ni-Co alloy has a double improvement on hydrogen absorption and desorption kinetics. Concretely, the alloy has an optimal hydrogen absorption temperature of 200 °C, at which it can absorb 5.5 wt. % H 2 within 40 s. Under the conditions, the capacity of absorption almost reaches the maximum reversible value (about 5.6 wt. %). Besides, the alloy has a dehydrogenation activation energy of 67.9 kJ/mol and can desorb 5.0 wt. % H 2 within 60 min at the temperature of 260 °C.