Fluorographene nanosheets enhanced hydrogen absorption and desorption performances of magnesium hydride

Abstract

Fluorographene (FG), which inherits the properties of graphene and fluorographite (FGi), was successfully fabricated through a simple sonochemical exfoliation route in N-methyl-2-pyrrolidone (NMP) and then MgH2-FG composite was prepared by ball milling. The dehydrogenation and rehydrogenation performances of MgH2-FG composite were investigated systematically comparing with as-received MgH2 and MgH2-G composite. It is found that the as-prepared FG exhibited a significant catalytic effect on the dehydrogenation and rehydrogenation properties of MgH2. The MgH2-FG composite can uptake 6.0 wt% H2 in 5 min and release 5.9 wt% H2 within 50 min at 300 °C, while the as-received MgH2 uptakes only 2.0 wt% H2 in 60 min and hardly releases hydrogen at the same condition. The hydrogen storage cycling kinetics in the first 10 cycles remains almost the same, indicating the excellent reversibility of the MgH2-FG composite. SEM analysis shows that the particle size of MgH2-FG composite was ∼200 nm, much smaller than that of as-received MgH2 (∼20 μm). TEM observations show that MgH2 particles were embedded in FG layers during ball milling. The dehydrogenation apparent activation energy for the MgH2 is reduced from 186.3 kJ mol−1 (as-received MgH2) to 156.2 kJ mol−1 (MgH2-FG composite). The catalytic mechanism has been proposed that F atoms in FG serve as charge-transfer sites and accelerate the rate of hydrogen incorporation and dissociation, consequently enhance the dehydrogenation and rehydrogenation properties of MgH2-FG composite. Furthermore, the FG can inhibit the sintering and agglomeration of MgH2 particle, thus it improves the cycling dehydrogenation and rehydrogenation of MgH2-FG composite.