In order to improve the hydrogen storage properties of MgH₂, the layered Ni₃ZnC_0.7 loaded TiO₂ composite with bamboo-like carbon nanotubes on surface is prepared by filtration followed with calcination. The MgH₂-2.5 wt% TiO₂/Ni₃ZnC_0.7 composite can absorb 4.13 wt% H₂ at 423 K and 600 s, and release 4.02 wt% H₂ at 573 K and 60 min. The hydrogen absorption/desorption activation energies are decreased to 41.92 and 95.18 kJ mol⁻¹ H₂, respectively. The hydrogen storage capacity exhibits little changes under different temperatures and pressures (110 cycles), clearly imply its cycle stability of this composite. The in-situ generated Mg₂Ni/Mg₂NiH₄ acts as a “hydrogen pump” providing additional channels for hydrogen diffusion and the presence of carbon nanotubes limits the aggregation and growth of Mg/MgH₂ particles. Moreover, multivalent Ti provides bridges and catalytically active sites for electron transfer between. During the broken process of Mg-H bonds, Bader charge maps indicate that H is bonded with Ti and Mg is bonded with O; After another MgH₂ absorbed, two H atoms are coordinated to Ti, implying that the TiO₂ acts as “charge regulator”. The deep understanding of the charge transfer between the MgH₂ and TiO₂ surface of the MgH₂/TiO₂/Ni₃ZnC_0.7 composite should provide new sight for designing MXene and Ni₃ZnC_0.7 derived catalysts.

MgH₂ is considered one of the most promising hydrogen storage materials because of its safety, high efficiency, high hydrogen storage quantity and low cost characteristics. But some shortcomings are still existed: high operating temperature and poor hydrogen absorption dynamics, which limit its application. Porous Ni₃ZnC_0.7/Ni loaded carbon nanotubes microspheres (NZC/Ni@CNT) is prepared by facile filtration and calcination method. Then the different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%) is added to the MgH₂ by ball milling. Among the three samples with different amount of NZC/Ni@CNT (2.5, 5.0 and 7.5 wt%), the MgH₂-5 wt% NZC/Ni@CNT composite exhibits the best hydrogen storage performances. After testing, the MgH₂-5 wt% NZC/Ni@CNT begins to release hydrogen at around 110 ℃ and hydrogen absorption capacity reaches 2.34 wt% H₂ at 80 ℃ within 60 min. Moreover, the composite can release about 5.36 wt% H₂ at 300 ℃. In addition, hydrogen absorption and desorption activation energies of the MgH₂-5 wt% NZC/Ni@CNT composite are reduced to 37.28 and 84.22 KJ/mol H₂, respectively. The in situ generated Mg₂NiH₄/Mg₂Ni can serve as a “hydrogen pump” that plays the main role in providing more activation sites and hydrogen diffusion channels which promotes H₂ dissociation during hydrogen absorption process. In addition, the evenly dispersed Zn and MgZn₂ in Mg and MgH₂ could provide sites for Mg/MgH₂ nucleation and hydrogen diffusion channel. This attempt clearly proved that the bimetallic carbide Ni₃ZnC_0.7 is a effective additive for the hydrogen storage performances modification of MgH₂, and the facile synthesis of the Ni₃ZnC_0.7/Ni@CNT can provide directions of better designing high performance carbide catalysts for improving MgH₂.