Ti 3 AlCN MAX for tailoring MgH 2 hydrogen storage material: from performance to mechanism

Many MXenes are efficient catalysts for MgH 2 hydrogen storage material. Nevertheless, the synthesis of MXenes should consume a large amount of corrosive HF to etch out the Al layers from the transition metal aluminum carbides or nitrides (MAX) phases, which is environmentally unfriendly. In this work, Ti 3 AlCN MAX without HF-etching was employed directly to observably enhance the kinetics and the cycling stability of MgH 2 . With addition of 10 wt% Ti 3 AlCN, the onset dehydrogenation temperature of MgH 2 was dropped from 320 to 205 °C, and the rehydrogenation of MgH 2 under 6 MPa H 2 began at as low as 50 °C. Furthermore, at 300 °C, it could provide 6.2 wt% of hydrogen in 10 min. Upon cycling, the composite underwent an activation process during the initial 40 cycles, with the reversible capacity increased from 4.7 wt% to 6.5 wt%. After that, the capacity showed almost no attenuation for up to 100 cycles. The enhancing effect of Ti 3 AlCN on MgH 2 was comparable to many MXenes. It was demonstrated that Ti 3 AlCN did not destabilize MgH 2 but acted as an efficient catalyst for MgH 2 . Ti 3 AlCN was observed to be the active sites for the nucleation and growth of MgH 2 and might also help in dissociation and recombination of hydrogen molecules. Such two factors are believed to contribute to the improvement of MgH 2 . This study not only provides a promising strategy for improving the hydrogen storage performances of MgH 2 by using noncorrosive MAX materials, but also adds evidence of nucleation and growth of MgH 2 on a catalyst. Graphical abstract