Ti3AlCN MAX for tailoring MgH2 hydrogen storage material: from performance to mechanism

Many MXenes are efficient catalysts for MgH2 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, Ti3AlCN MAX without HF-etching was employed directly to observably enhance the kinetics and the cycling stability of MgH2. With addition of 10 wt% Ti3AlCN, the onset dehydrogenation temperature of MgH2 was dropped from 320 to 205 & DEG;C, and the rehydrogenation of MgH2 under 6 MPa H-2 began at as low as 50 & DEG;C. Furthermore, at 300 degrees 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 Ti3AlCN on MgH2 was comparable to many MXenes. It was demonstrated that Ti3AlCN did not destabilize MgH2 but acted as an efficient catalyst for MgH2. Ti3AlCN was observed to be the active sites for the nucleation and growth of MgH2 and might also help in dissociation and recombination of hydrogen molecules. Such two factors are believed to contribute to the improvement of MgH2. This study not only provides a promising strategy for improving the hydrogen storage performances of MgH2 by using noncorrosive MAX materials, but also adds evidence of nucleation and growth of MgH2 on a catalyst.