Improved reversible dehydrogenation properties of 2LiBH4–MgH2 composite by milling with graphitic carbon nitride

• A new 2LiBH4–MgH2–C3N4 composite is prepared by optimized procedures.
• C3N4 addition improves reversible dehydrogenation property of the LiBH4–MgH2 composite.
• C3N4 addition eliminates the incubation period between the two dehydrogenation stages.
• The promotion mechanism of C3N4 additive is discussed.

The 2LiBH4–MgH2 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 (C3N4) as a metal-free additive was added to the 2LiBH4–MgH2 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 C3N4 additive can eliminate the incubation period between two dehydrogenation steps and thus markedly enhance the dehydrogenation kinetics of the LiBH4–MgH2 composite. Further cyclic study found that the composite with C3N4 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 C3N4 additive could react with both LiBH4 and MgH2 in heating process, and the resulting products may improve the reversible dehydrogenation property of the composite system.

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