Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH 2 by the MnO x -Coated Ti 2 C T x Catalyst with Optimized Ti-H Bond Stability.

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH 2 , but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose T x density control of MXene-based catalysts and MnO x coating as a promising solution. The MnO x @Ti 2 C T x -catalyzed Mg/MgH 2 can release 5.97 wt % H 2 at 300 °C in 3 min and 5.60 wt % H 2 at 240 °C in 15 min with an activation energy of 75.57 kJ·mol -1 . In addition, the samples showed excellent de/hydrogenation-cycle stability, and the degradation of hydrogen storage capacity is negligible even after 100 cycles. DFT calculations combined with XPS analysis showed that the T x defect on the surface of the MnO x @Ti 2 C T x catalyst could optimize the strength of the Ti-H bond, accelerating both hydrogen dissociation and diffusion processes. The catalyst's surface properties were protected by the MnO x coating, achieving high chemical and catalytic stability. These findings offer a strategy for surface structure optimization and protection of MXene-based catalysts, realizing controllable catalyst-hydrogen bond strength.