Charge transfer between the MgH₂ and TiO₂ surface of the MgH₂/TiO₂/Ni₃ZnC_0.7 composite with good cyclic reliability

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.