Improved reversible dehydrogenation properties of 2LiBH_4-MgH_2 composite by milling with graphitic carbon nitride

摘要

The 2LiBH_4-MgH_2 reactive hydride composite is a promising hydrogen storage system due to the combined high hydrogen capacity and relatively moderate reaction enthalpy. However, the sluggish de/rehydrogenation kinetics severely impedes its practical applications. In this study, graphitic carbon nitride (C_3N_4) as a metal-free additive was added to the 2LiBH_4-MgH_2 composite and examined with respect to the promoting effect on the hydrogen storage properties of the composite. Our study found that mechanically milling with small amount of C_3N_4 additive can eliminate the incubation period between two dehydrogenation steps and thus markedly enhance the dehydrogenation kinetics of the LiBH_4-MgH_2 composite. Further cyclic study found that the composite with C_3N_4 additive exhibits improved cyclic dehydrogenation property although it also shows capacity loss upon cycling, particularly in the second cycle. Combined dehydrogenation property, phase analysis and a series of designed experiments suggested that the C_3N_4 additive could react with both LiBH_4 and MgH_2 in heating process, and the resulting products may improve the reversible dehydrogenation property of the composite system.