Crystalline TiB2: an efficient catalyst for synthesis and hydrogen desorption/absorption performances of NaAlH4 system

Abstract

High hydrogen pressure and desorption/absorption temperature retard the practical applications of the NaAlH₄ system. To ease these problems, we successfully synthesize a crystalline TiB₂ catalyst to catalyze the synthesis of NaAlH₄. The weight percentage of synthesized nanocrystalline NaAlH₄ is as high as 89 wt%. More interestingly, a dramatically reduced of desorption/absorption temperature is achieved with the efficient TiB₂ catalyst. Thermodynamic analyses show that the onset dehydrogenation temperature of TiB₂–NaAlH₄ mixture is lowered to about 70 °C, which is lower than the pristine system. The activation energy of TiB₂–NaAlH₄ mixture calculated by Arrhenius equation is only 56.28 kJ mol⁻¹. In addition, as-prepared NaAlH₄ can be recharged almost quantitatively under remarkably mild conditions (90 °C and 4 MPa hydrogen pressure). The improvement of hydrogen storage and release properties is considerably pronounced under low-pressure and low-temperature conditions. Moreover, preliminary research about the catalytic mechanism of TiB₂ is also discussed.