Interfacial charge transfer-induced catalytic effect of Ti2C MXene for effective hydrogen storage in magnesium

Abstract

Solid state hydrogen storage in the form of MgH2 has numerous advantages such as high energy density, low cost and abundance in earth making it a promising hydrogen storage option for fuel cells and portable power devices. Despite these benefits, its practical application is hampered by slow sorption kinetics and high operating temperature. To address these issues, catalytic additives such as transition metals can be introduced to reduce energy barriers. The transition metal-based 2D material MXene has gained attention as a catalytic support for MgH2, however it presents a challenge of oxidation of Mg and increased dead mass resulting from surface functional groups formed during the etching step in aqueous acid. This study aims to overcome these issues by utilizing molten-salt derived MXene followed by removing functional groups and simultaneously forming Mg@Ti2C composites in reductive environment. Specifically, MXene etched in molten chloride salt primarily contains a -Cl functional group, which has a relatively weak bond strength compared to conventional MXenes, thereby enabling exposure of the Ti metallic surface and forming a Ti-Mg catalytic interface. The metal-support charge transfer is revealed by XPS and Ti L-edge NEXAFS measurement which confirms Ti2C MXene worked as catalytic support. The resulting Mg@Ti2C composites exhibit excellent H2 desorption kinetics and cycling stability which makes it feasible hydrogen storage medium for upcoming applications.