Catalytic effect of graphene on the hydrogen storage properties of Mg-Li alloy

Abstract

The Mg-Li-xgraphene(Gp) (x = 0,1,3,5) composites were synthesized by sintering and ball-milling, and the catalytic effect of the graphene on the hydrogen storage properties of the Mg-Li-xGp(x = 0,1,3,5) composites was investigated. Experimental results indicated that the addition of the graphene enhanced the reversible hydrogenation reaction of the Mg-Li alloy and reduced significantly the onset hydrogenation/dehydrogenation temperature of the Mg-Li alloy. For example, the reversible hydrogenation reaction occurred in the case of the Mg-Li-xGp(x = 3,5) composites at 300 °C, while it did not occur in the case of the Mg-Li alloy at the same temperature. The onset temperature of dehydrogenation for Mg-Li alloy was about 338 °C, by comparison, and the onset temperature of dehydrogenation for Mg-Li-xGp(x = 3,5) composites decreased to 276 °C. In addition, the Mg-Li-xGp(x = 1,3,5) composites could release more than 90% of the hydrogen absorbed when heated at a rate of 2 °C/min from room temperature to 353 °C, while only 39% of the hydrogen absorbed in the Mg-Li alloy was released in the same condition, which is resulted from the decrease of the apparent activation energy (Ea) of dehydrogenation for the Mg-Li alloy with the graphene addition. Graphene acts as a catalyst, thereby lowering the reaction barrier for dehydrogenation of the Mg-Li alloy, which in turn promotes the reversible hydrogenation/dehydrogenation reaction of the alloy.