Room-Temperature Hydrogen Absorption of Titanium with Surface Modification by Organic Solvents

As a thermochemical heat storage system by hydrogenating reaction of titanium (Ti), surface modification methods are investigated in order to improve the hydrogen absorption kinetics of Ti. It is clarified that Ti with the fresh surface has high reactivity with not only oxygen and water but also hydrogen. However, the reactivity with hydrogen is lost after 1 day even under a highly purified Ar atmosphere. Typical catalysts for hydrogen dissociation observed in Mg systems are not effective for Ti. On the other hand, when Ti powder was ball-milled with acetone, the surface is effectively modified, and the characteristic surface shows high reactivity and selectivity for hydrogen even at room temperature. In X-ray photoelectron spectroscopy of the Ti powder, the metallic state of Ti stabilized in this characteristic surface can be observed, although a pristine surface showed only a Ti⁴⁺ state as TiO₂. This surface is composed of the TiC precursor, transforming to the crystalline TiC phase after annealing at 650 °C.