Ti3C2Tx MXene-catalyzed near-eutectic Mg-Ni-La composites: Synergistic phase-boundary and in-situ “hydrogen pump” effects for advanced low-temperature hydrogen storage

The near eutectic Mg 87 Ni 11.5 La 1.5 alloy was prepared by microalloying and gas-shielded melting. The microstructure of this alloy consists of alternating distribution of Mg, Mg 2 Ni and Mg 12 La eutectic phases with a size of less than 1 μm. And then the near-eutectic Mg 87 Ni 11.5 La 1.5 alloy was doped with 1 wt.% Ti 3 C 2 T x MXene catalyst by mechanical ball milling. The Mg 87 Ni 11.5 La 1.5 -Ti 3 C 2 T x composite exhibits remarkable low-temperature hydrogen absorption and desorption performance. Specifically, the composite delivers a hydrogen absorption capacity of 1.84 wt.% at room temperature. At 373 K, the hydrogen absorption capacity of the composite reaches 4.88 wt.%, 2.38 wt.% higher than that of the original alloy. At 473 K, its hydrogen desorption capacity is 1.90 wt.%, which is 0.39 wt.% higher relative to the original alloy. The hydrogen desorption activation energy is lowered to 53.88 kJ·mol −1 after Ti 3 C 2 T x modification, compared with 75.33 kJ·mol −1 for the original alloy. Abundant phase boundaries of eutectic alloy provide sufficient hydrogen diffusion paths and synergistic catalytic active sites. The uniformly dispersed Mg 2 NiH 4 on composite surfaces serves as an in-situ generated catalytic phase. The Ti contained in Ti 3 C 2 T x acts as an in-situ “hydrogen pump” during hydrogenation, thereby promoting hydrogen diffusion. Its multivalent characteristic facilitates electron transfer between Mg 2+ and H − . Synergistic effects of above behaviors comprehensively enhance hydrogen storage properties of composite. Furthermore, special structure of Ti 3 C 2 T x can inhibit the agglomeration of the material and guarantee the smooth hydrogen diffusion channel, so that the composite material retains 96.70 % hydrogen storage capacity after 100 hydrogen absorption/desorption cycles, demonstrating excellent cycling stability.