Catalytic effect of sandwich-like Ti₃C₂/TiO₂(A)-C on hydrogen storage performance of MgH₂

A sandwich-like Ti₃C₂/TiO₂(A)-C prepared through a facile gas-solid method was doped into MgH₂ by ball milling. Ti₃C₂/TiO₂(A)-C shows a far superior catalytic effect on the hydrogen storage of MgH₂ than individual Ti₃C₂ or TiO₂(A)-C, assigning as a synergistic catalysis between Ti₃C₂ and TiO₂(A)-C. For example, the peak dehydrogenation temperature of MgH₂-5 wt% Ti₃C₂/TiO₂(A)-C is reduced to 308 °C, much lower than that of MgH₂-5 wt% Ti₃C₂ (340 °C) or MgH₂-5 wt% TiO₂(A)-C (356 °C). After dehydrogenation, the dehydrogenated MgH₂-5 wt% Ti₃C₂/TiO₂(A)-C can uptake approximately 4 wt% of hydrogen within 800 s at 125 °C, while for the dehydrogenated MgH₂-5 wt% Ti₃C₂ and MgH₂-5 wt% TiO₂(A)-C, only 3 wt% and 2.65 wt% hydrogen content can be obtained, respectively. Besides this, MgH₂-5 wt% Ti₃C₂/TiO₂(A)-C exhibits the lowest apparent activation energies (42.32 kJ mol^-1 H₂ for the hydrogen absorption and 77.69 kJ mol^-1 H₂ for the hydrogen desorption), which can explain the excellent hydrogen ab/desorption kinetic properties. The synergetic effects between the special layered structure and multiple valence titanium compounds (Ti⁴⁺, Ti³⁺, Ti²⁺, Ti⁰) verified by the x-ray photoelectron spectroscopy results are responsible for the catalytic mechanism on the hydrogen storage of MgH₂. This study also supplies innovative insights into designing high efficiency MXene derivative catalysts in hydrogen storage.