Utlra-fast hydrolysis performance of MgH2 catalyzed by Ti-Zr-Fe-Mn-Cr-V high-entropy alloys

Abstract

Hydrogen energy is one of the ideal energy alternatives and the upstream of the hydrogen industry chain is hydrogen production, which can be achieved via the reaction of inorganic materials with water, known as hydrolysis. Among inorganic materials, the high hydrogen capacity for hydrolysis of MgH2 (15.2 wt%) makes it a promising material for hydrogen production via hydrolysis. However, the dense Mg(OH)2 passivation layer will block the reaction between MgH2 and the solution, resulting in low hydrogen yield and sluggish hydrolysis kinetics. In this work, the hydrogen yield and hydrogen generation rate of MgH2 are considerably enhanced by adding Ti-Zr-Fe-Mn-Cr-V high-entropy alloys (HEAs) for the first time. In particular, the MgH2-3wt% TiZrFe1.5MnCrV0.5 (labelled as MgH2-3wt% Fe1.5) composite releases 1526.70 mL/g H2 within 5 min at 40 °C, and the final hydrolysis conversion rate reaches 95.62% within 10 min. The mean hydrogen generation rate of the MgH2-3wt% Fe1.5 composite is 289.16 mL/g/min, which is 2.38 times faster than that of pure MgH2. Meanwhile, the activation energy of the MgH2-3wt% Fe1.5 composite is calculated to be 12.53 kJ/mol. The density functional theory (DFT) calculation reveals that the addition of HEAs weakens the Mg–H bonds and accelerates the electron transfer between MgH2 and HEAs. Combined with the cocktail effect of HEAs as well as the formation of more interfaces and micro protocells, the hydrolysis performance of MgH2 is considerably improved. This work provides an appealing prospect for real-time hydrogen supply and offers a new effective strategy for improving the hydrolysis performance of MgH2.