Electronic structure regulation of N-doped MXene-Co catalyst: Optimizing Co-H bonding to synergistically catalyze hydrogen storage of MgH2.

The practical application of magnesium hydride (MgH2) for solid-state hydrogen storage is fundamentally bottlenecked by its sluggish kinetics and severe performance degradation over prolonged cycling. Although two dimensional (2D) MXenes show great promise in modifying MgH2, the catalytic performance is hindered by strong hydrogen trapping on pristine surfaces. While loading transition metals can resolve this issue, their inherently strong metal‑hydrogen bonds introduce a kinetic hurdle. To address this issue, we report a green strategy to construct an N-doped Ti3C2Tx MXene-Co (N-Mx-Co) catalyst. Experimental and density functional theory (DFT) calculations reveal an efficient synergistic catalytic mechanism. Specifically, anchoring Co effectively inhibits the formation of excessively strong TiH bonds at the active sites of pristine MXene. Concurrently, the highly electronegative N dopants induce local electron redistribution to optimize the CoH bond strength. This structural and electronic modulation lowers the energy barriers for hydrogen migration and desorption. Additionally, a dynamic "hydrogen pump" effect is driven by the conversion between Mg2Co and Mg2CoH5, facilitating H-atom migration, and multivalent Ti species drive fast electron exchange to effectively weaken the MgH binding energy. Additionally, the 2D layered structure of the MXene provides spatial confinement, maintaining the prolonged cyclic durability of the composite. Benefiting from this synergistic catalysis, the apparent activation energy of the N-Mx-Co/MgH2 composite is lowered by 37.16%, releasing 6.42 wt% H2 in 5 min at 300 °C, maintaining an exceptional capacity retention of 95.9% over 350 cycles. This structural and electronic co-regulation strategy presents a practical approach to overcome the kinetic and cyclic degradation issues of MgH2.