Enhanced Hydrogen Storage Performance of LiBH₄−SiO₂−TiF₃ Composite

Abstract

The destabilization approach for SiO2-doped LiBH4 hydrogen storage composite is identified as 4LiBH4 + 2SiO2 → Li4SiO4 + 4B + Si + 8H2, and Li4SiO4 is the thermodynamic obstacle for its reverse action. TiF3 was doped in the composite for avoiding the formation of Li4SiO4 and thus enhancing the reversible hydrogen storage properties. Experimental analysis on LiBH4−SiO2−TiF3 composite was performed via thermogravimetry (TG), temperature programmed desorption (TPD), mass spectral analysis (MS), differential scanning calorimetry (DSC), isothermal sorption, and powder X-ray diffraction (XRD). For LiBH4−20 wt % SiO2−30 wt % TiF3 composite, the dehydrogenation temperature starts from 70 °C and decreases by an average of 100 °C from that of LiBH4−20 wt % SiO2. Its maximum amount attains 8.3 wt % below 500 °C. The whole dehydrogenation can be regarded as a two-step process: (i) preferential reaction (3LiBH4 + TiF3 → 3LiF + TiB2 + B + 6H2) occurring at around 70 °C, and (ii) principal reactions occurring simultaneously both at interface (LiBH4 + TiF3 + SiO2) and inside the bulk (self-decomposition of LiBH4). Doped TiF3 noticeably reduces the energy activation of the reaction at interface. However, the reaction inside the bulk is the rate-controlled process. This composite also demonstrates the ability of rehydrogenation under the pressure of 4.5 MPa. The hydrogen absorption is temperature-dependent and reaches 4 wt % H2 within 14 000 s at 500 °C.