The anionic Tx defects of Nb2CTx MXene as the effective catalytically active center for the Mg-based hydrogen storage materials

While early transition metal-based materials, such as MXene, has emerged as an efficient catalyst for the Mg-based hydrogen storage materials, their strong interaction with hydrogen resulted in the high hydrogen diffusion barrier, hindering further improvement of catalytic activity. A MXene is characterized by rich anionic groups on its surface, significantly affecting electronic and catalytic functionalities. Using Nb2CTx as an example, we herein illustrate the critical role of anionic Tx defects on controlling hydrogen dissociation and diffusion processes in Mg-based hydrogen storage materials. The hydrogen desorption properties of MgH2 can be significantly enhanced by utilizing Tx controllable Nb2CTx, and it can release 3.57 wt.% hydrogen within 10 min under 240 °C with the reduced dehydrogenation activation barrier. It also realized stable de/hydrogenation reactions for at least 50 cycles. DFT studies combined with kinetic analysis revealed that the catalyst‒hydrogen interaction could be systematically controlled by optimizing surface Tx defect density, accelerating the hydrogen dissociation and diffusion processes at the same time. These results demonstrate that the Tx defects serve as the effective catalytically active centers of Nb2CTx, offering a flexible catalyst design guideline.