Excellent catalytic effects of highly crumpled graphenenanosheets on hydrogenation/dehydrogenation of magnesium hydride

Abstract

Highly crumpled graphene nanosheets (GNS) with a BET surface area as high as 1159 m(2) g(-1) was fabricated by a thermal exfoliation method. A systematic investigation was performed on the hydrogen sorption properties of MgH(2)-5 wt% GNS nanocomposites acquired by ball-milling. It was found that the as-synthesized GNS exhibited a superior catalytic effect on hydrogenation/dehydrogenation of MgH(2). Differential Scanning Calorimetry (DSC) and isothermal hydrogenation/dehydrogenation measurements indicated that both hydrogen sorption capacity and dehydrogenation/hydrogenation kinetics of the composites improved with increasing milling time. The composites MgH(2)-GNS milled for 20 h can absorb 6.6 wt% H(2) within 1 min at 300 °C and 6.3 wt% within 40 min at 200 °C, even at 150 °C, it can also absorb 6.0 wt% H(2) within 180 min. It was also demonstrated that MgH(2)-GNS-20 h could release 6.1 wt% H(2) at 300 °C within 40 min. In addition, microstructure measurements based on XRD, SEM, TEM as well as Raman spectra revealed that the grain size of thus-prepared MgH(2)-GNS nanocomposites decreased with increasing milling time, moreover, the graphene layers were broken into smaller graphene nanosheets in a disordered and irregular manner during milling. It was confirmed that these smaller graphene nanosheets on the composite surface, providing more edge sites and hydrogen diffusion channels, prevented the nanograins from sintering and agglomerating, thus, leading to promotion of the hydrogenation/dehydrogenation kinetics of MgH(2).

Influences and mechanisms of graphene-doping on dehydrogenation properties of MgH2: Experimental and first-principles studies

“…It is found that there are two or three endothermic peaks for these samples. The identification of multiple peaks may be due to multimodal particle size distribution formed during milling as has been previously reported in the literature [15,16]. For the pure MgH 2 milled for 6 h, the dehydrogenation peak temperatures are 429 C and 450 C, respectively, while for the milled MgH 2 -G samples, their dehydrogenation peak temperatures shift to the much lower ones with increasing milling time except for the highest peak.…”

“…Noticeably, G has also been confirmed to be an excellent catalyst on hydrogen desorption and adsorption of MgH 2 [15e17]. For example, Yuan et al [15] fabricated highly crumpled GNS (graphene nanosheets) and investigated the hydrogen sorption properties of MgH 2 -5 wt%GNS nanocomposites prepared by ball milling. It was found that the GNS exhibited a superior catalytic effect on hydrogenation/dehydrogenation kinetics of MgH 2 .…”

Porous Ni nanofibers with enhanced catalytic effect on the hydrogen storage performance of MgH2

“…[32][33][34][35] Plotting ln[−ln(1−α)] against ln t in the range 0.2 α0.5 yields a straight line, where ƞ = slope and k = e intercept/slope . A hydrogen desorption fraction ranging from 0.2-0.5 was adopted to fit the kinetic curves.…”

Catalytic Application of Carbon‐based Nanostructured Materials on Hydrogen Sorption Behavior of Light Metal Hydrides

“…The barrier is lowered to 1.05 ev and the atomic hydrogen is also diffuse easily into the sublayer through the channels [92] due to which hydrogen dissociation/recombination in presence of GNS is facilitated and possible below 300°C. Liu et al [91]. clearly demonstrated that the small GNS dispersed in an irregular and disorderly manner in the composite after ball milling.…”

“…Recently, the catalytic effect of graphene on sorption behavior of MgH 2 was reported by Liu et al [91]. They investigated the catalytic effect of graphene nanosheets (GNS) on the improvement of sorption behavior of MgH 2 .…”