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

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose density control of MXene-based catalysts and MnO coating as a promising solution. The MnO@TiC-catalyzed Mg/MgH can release 5.97 wt % H at 300 °C in 3 min and 5.60 wt % H at 240 °C in 15 min with an activation energy of 75.57 kJ·mol. 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 defect on the surface of the MnO@TiC 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 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.