Room-Temperature Hydrogen Absorption of Ti with Robust Surface Coated by Hexagonal Boron Nitride

Titanium (Ti) absorbs hydrogen (H2) with the reaction enthalpy of −142 kJ/mol H2, which is larger than that of the reaction between magnesium and H2. Therefore, the Ti–H2 system is a promising system as thermochemical heat storage for high temperature with high energy density. In order to realize the Ti–H2 system as a thermochemical heat storage, the reaction kinetics of the hydrogen absorption must be improved. It is previously reported that Ti can absorb H2 even at room temperature, when the Ti surface was modified by graphite. However, the reactivity of Ti with H2 was lost after the dehydrogenation due to the transformation of the modified surface to titanium carbide. The modified surface with high thermal stability is required to obtain high cycle performance of the hydrogen absorption/desorption. In this work, hexagonal boron nitride (h-BN) was investigated as an agent for the surface modification of Ti. The Ti modified by h-BN can absorb approximately 3 wt % of H2 at 40 °C within 10 min. In addition, the functional surface was kept even after the dehydrogenation at 580 °C. By the microscopic analyses, it was found that the turbostratic BN and nitride phases are formed on the Ti surface, showing the selective hydrogen absorption effects. Thus, the robust surface of Ti with high reactivity for H2 was obtained by using the surface modification using h-BN.