Improved reversible dehydrogenation of LiBH_4-MgH_2 composite by the synergistic effects of Al and MgO

摘要

In this paper, we report a novel method of improving the reversible dehydrogenation properties of the 2LiBH_4-MgH_2 composite. Our study found that mechanically milling with small amount of Al powder can markedly shorten or even eliminate the problematic incubation period that interrupts the dehydrogenation steps of the 2LiBH_4-MgH_2 composite. But the resulting composite showed serious kinetics degradation upon cycling. In an effort to solve this problem, we found that combined usage of small amounts of Al and MgO enabled the 2LiBH_4-MgH_2 composite to rapidly and reversibly deliver around 9 wt% hydrogen at 400 ℃ under 0.3 MPa H_2, which compares favorably with the dehydrogenation performance of the composites with transition-metal additives. A combination of phase/ microstructural analyses and series of control experiments has been conducted to gain insight into the promoting effects of Al and MgO. It was found that Al and MgO additives act as precursor and promoter for the formation of AlB_2 heterogeneous nucleation sites, respectively.