Two-dimensional TiO2 quantum dots for efficient hydrogen storage: Effect of doping and vacancies

The electronic and optical properties and hydrogen storage capacity of doped two-dimensional TiO2 quantum dots are studied using density functional theory computations. The considered dopants are C, S, N, Fe, Ni, and Zn. Temperature stability is confirmed at 500 K according to ab initio molecular dynamics simulations. Doping and vacancy formation increase the energy gap due to the relaxation of Ti-atoms by additional electrons from the dopants or surface reconstruction after removing O or Ti atoms. The UV–Vis absorption spectra imply that the dominant absorption peak experiences a blue shift after doping and vacancies. The pristine TiO2 is promising for hydrogen storage with suitable adsorption energy that can be enhanced by doping. We obtained a gravimetric adsorption capacity of 6.23 wt% which is higher than the 6.0 wt% issued by the US Department of Energy. Therefore, the high adsorption capacity/energy and thermal stability render TiO2 nanodots promising for efficient H2-storage devices.