# The Application of Nano Titanium Dioxide for Hydrogen Production and Storage Enhancement
## 2 Titanium Dioxide
### Exploiting the TiO\({}_{2}\) Properties for Hydrogen Storage
The MgH\({}_{2}\)-Co/TiO\({}_{2}\) composite showed an absorption of 6.07 wt% H\({}_{2}\) within 10 min at 165 \({}^{\circ}\)C under 60 bar of H\({}_{2}\) pressure and a dehydrogenation peak temperature of 235.2 \({}^{\circ}\)C. A sandwich-like structure composed of Ti\({}_{3}\)C\({}_{2}\) and carbon-supported anatase TiO\({}_{2}\) (Ti\({}_{3}\)C\({}_{2}\)/TiO\({}_{2}\)(A)-C) was developed by [PERSON] et al. [55] in order to exploit the laminar MXene and the corresponding metal oxide to enhance the hydrogen absorption and desorption kinetics of MgH\({}_{2}\). The Ti\({}_{3}\)C\({}_{2}\)/TiO\({}_{2}\)(A)-C structure was prepared using a heat treatment. The catalyst-doped MgH\({}_{2}\) composites with 5 wt% of Ti\({}_{3}\)C\({}_{2}\)/TiO\({}_{2}\)(A)-C released approximately 5 wt% hydrogen within 1700 s at 250 \({}^{\circ}\)C under 0.05 MPa of hydrogen pressure, with a larger rate constant of 0.258 wt% min\({}^{-1}\). An uptake of approximately 4 wt% hydrogen within 800 s at 125 \({}^{\circ}\)C, under 3 MPa hydrogen pressure, was also observed. Unlike the preparation of the TiO\({}_{2}\)/MXene heterostructure via the heat treatment of MXene, [PERSON] et al. [13] also developed self-assembled TiO\({}_{2}\)/Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) heterostructures through a one-step ultrasonic method at room temperature. The TiO\({}_{2}\) nanoparticles were self-assembled onto a few layers of Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\). The TiO\({}_{2}\)/Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\)-MgH\({}_{2}\) composite with 5 wt% of TiO\({}_{2}\)/Ti\({}_{3}\)C\({}_{2}\)T\({}_{\rm x}\) achieved the fastest dehydrogenation and hydrogenation kinetics, showing a hydrogen desorption of 5.98 wt% within 600 s at 300 \({}^{\circ}\)C and a hydrogen absorption of 5.90 wt% within 1200 s at 175 \({}^{\circ}\)C. A catalyst composed of TiO\({}_{2}\) nanoparticles deposited on the pore wall of a three-dimensionally ordered macroporous (3 DOM) structure was synthesized by [PERSON] et al. [56]. It was observed that the 3 DOM TiO\({}_{2}\) catalyst improved the hydrogen storage properties of MgH\({}_{2}\). The MgH\({}_{2}\)-3 DOM TiO\({}_{2}\) composite showed a hydrogen desorption of 5.75 wt% within 1000 s at 300 \({}^{\circ}\)C. A hydrogen absorption of 4.17 wt% within 1800 s even at 100 \({}^{\circ}\)C was observed. [PERSON] et al. [64] investigated the effects of TiO\({}_{2}\) nanorods on the absorption/desorption properties of MgH\({}_{2}\). The TiO\({}_{2}\) nanorods were produced through titanate nanotube heat treatment, whereas titanate nanotubes were synthesized via the alkaline hydrothermal route using commercial TiO\({}_{2}\) anatase as a starting material. At 350 \({}^{\circ}\)C, the MgH\({}_{2}\)-TiO\({}_{2}\) nanorod composite showed a hydrogen absorption of 5.5 wt% after 10 min under 10 bar of hydrogen pressure. Furthermore, it was observed that after 5 min at 350 \({}^{\circ}\)C under 0.1 bar of hydrogen pressure, the composite desorbed around 100% of the absorbed hydrogen. A Ni/TiO\({}_{2}\) cocatalyst with a Ni@TiO\({}_{2}\) core-shell structure was synthesized by [PERSON] et al. [65] via a modified hydrothermal synthesis method. The MgH\({}_{2}\)-Ni/TiO\({}_{2}\) composite with 5 wt% of Ni/TiO\({}_{2}\) allowed a hydrogen absorption of 4.50 wt% to be obtained at 50 \({}^{\circ}\)C under an initial hydrogen pressure of 3.0 MPa and a hydrogen desorption of 5.24 wt% in 1800 s at 250 \({}^{\circ}\)C under 0.005 MPa of hydrogen pressure [65]. [PERSON] et al. [66] synthesized and investigated three-dimensional flower-like TiO\({}_{2}\) (fl-TiO\({}_{2}\)) and three-dimensional flower-like carbon-wrapped TiO\({}_{2}\) (fl-TiO\({}_{2}\)@C) as the catalysts for MgH\({}_{2}\). Both catalysts enhanced the hydrogen sorption kinetics of MgH\({}_{2}\). Superior desorption kinetics of the MgH\({}_{2}\)-fl-TiO\({}_{2}\)@C composite compared to the MgH\({}_{2}\)-fl-TiO\({}_{2}\) composite were observed.