TiVNb-based high entropy alloys as catalysts for enhanced hydrogen storage in nanostructured MgH2

Abstract

Magnesium hydride (MgH₂) is a promising candidate for hydrogen storage, but suffers from its sluggish de/hydrogenation kinetics. Catalytic addition is considered one of the most effective methods to improve the kinetics of Mg-based hydrides. Herein, the equiatomic high entropy alloys (HEAs), namely, TiVNbZrFe, TiVNbZrNi, and TiVNbCrNi, are used as catalysts for MgH₂. The results show that HEAs exhibit the C14 Laves structure and provide excellent catalytic impact. Among these HEA catalysts, the TiVNbZrFe alloy shows a superior catalytic effect in improving the de/hydrogenation kinetics and cycling properties of MgH₂. In particular, MgH₂–TiVNbZrFe starts to release hydrogen at about 209 °C, nearly 170 °C lower than that of the pure MgH₂. Also, it can be hydrogenated at room temperature and under 1 bar hydrogen pressure. Moreover, a stable reversible capacity up to 6.16 wt% is observed after 100 cycles. The apparent activation energy of dehydrogenating MgH₂–TiVNbZrFe can be reduced to 63.03 kJ mol⁻¹, which is about 90 kJ mol⁻¹ lower than that of pure MgH₂.