High catalytic activity derived from TiNbAlC MAX towards improving the hydrogen storage properties of MgH2.

MXenes are great catalysts for MgH 2 hydrogen storage material. Nevertheless, the synthesis of MXenes needs a large quantity of corrosive HF solution to remove the Al layers from the MAX materials, which is harmful to the environment. In this work, TiNbAlC MAX was employed without HF-treatment to tailor the hydrogen storage of MgH 2. The MgH 2 + 10 wt% TiNbAlC composite was prepared by ball milling. The addition of 10 wt% TiNbAlC greatly reduces the onset temperature of MgH 2 desorption from 332 °C to 197 °C. The composite can desorb 6.2 wt% of H 2 in 10 min at a constant temperature of 300 °C. Moreover, the dehydrided MgH 2 + 10 wt% TiNbAlC composite can start to absorb hydrogen at room temperature under a H 2 pressure of 6 MPa. The hydrogen desorption activation energy of the composite was calculated by Kissinger's method to be 101 kJ mol−1. Microstructures studies demonstrated that TiNbAlC will partially react with MgH 2 /H 2 to form TiH 1.971 , which can act as a "hydrogen pump" to facilitate the hydrogen sorption of MgH 2. This work suggests that MAX materials are good catalysts for hydrogen storage of MgH 2 and provides new insight into the role of MAX phase in tailoring the hydrogen storage of Mg-based hydrogen storage materials. [Display omitted] • TiNbAlC can significantly enhance the hydrogen storage of MgH 2. • Enhancing effect of TiNbAlC is comparable to many MXenes • TiNbAlC partially transform to active TiH 1.971. • TiH 1.971 acts as a "hydrogen pump" for hydrogen sorption of MgH 2. [ABSTRACT FROM AUTHOR]