Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH₂ by the MnO_<i>x</i>-Coated Ti₂C<i>T</i>_<i>x</i> Catalyst with Optimized Ti–H Bond Stability

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH₂, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose <i>T</i>_<i>x</i> density control of MXene-based catalysts and MnO_<i>x</i> coating as a promising solution. The MnO_<i>x</i>@Ti₂C<i>T</i>_<i>x</i>-catalyzed Mg/MgH₂ can release 5.97 wt % H₂ at 300 °C in 3 min and 5.60 wt % H₂ 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 <i>T</i>_<i>x</i> defect on the surface of the MnO_<i>x</i>@Ti₂C<i>T</i>_<i>x</i> 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_<i>x</i> 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.