Room-Temperature Hydrogen Uptake by TiO2 Nanotubes

TiO2 nanotubes can reproducibly store up to ~2 wt % H2 at room temperature and 6 MPa. However, only about 75% of this stored hydrogen can be released when the hydrogen pressure is lowered to ambient conditions, suggesting that both physisorption and chemisorption are responsible for the hydrogen uptake. FTIR spectroscopy, temperature-programmed desorption (TPD), and pressure-composition (P-C) isotherms suggest that 75% of the H2 is physisorbed and can be reversibly released upon pressure reduction. Approximately 13% is weakly chemisorbed and can be released at 70 °C as H2, and ~12% is bonded to oxide ions and released only at temperatures above 120 °C as H2O.