| MgH2 has been received as the most potential hydrogen storage materials due to its high H-containing content of 7.6 wt%and good reversibility;but its applications were blocked by the high thermodynamic stability and kinetics barriers.The catalytic doping is an effective method for improving the hydrogen storage properties of MgH2 However,the correlations among close contacts with catalysts,morphology,supports and sorption properties of MgH2 are still unclear,especially for their atomtic interactions and interfacial coupling effects without being reported.Therefore,based on the review of solid H-storage mechanisms and the developments of improving hydrogen storage in MgH2,we first designed and bulit the micro/nano-structure metal catalyzed MgH2 systems by solid-state mechanical ball-milling,and then studied systematically the effects and their intrinsic mechanisms of size,morphology,atomic interactions and interfacial couplings on the hydrogen storage properties of MgH2 by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),high-angle annular dark-field scanning transmission electron microscopy(HADDF-STEM),synchrotron radiation X-ray absorption spectrum(SR-XAS),pressure-composition-temperature(PCT)testing techniques,and so on.The key conclusions are summarized as follows:(1)The spacial distributions and close contacts of Ni catalysts with MgH2 could be controlled effectively by the change of particle size of catalysts and milling times.It is found that the hydrogen storage properties of MgH2 highly depend on its close contact with the Ni catalysts,i.e.,more uniform distributions of catalyst,more being in close contacts between hydride and catalyst,and more easily to hydrogen storage in MgH2.As compared to pure one,the onset desorption of nano-Ni doped MgH2 is reduced by?180? while the kinetics is enhanced by six times(2)The morphology of graphene supported Ni cataysts was adjusted by Co doping through three-steps of doped precursor,milling and carbon-thermal reduction.Along with the increase of Co contents,the sphere structures transfer to nanosheets and further to films.The catalytic activity of nanosupported Co-Ni catalysts is found to be related to the compostion and morphology,where the morphology plays a dominant role.The activity of Ni nanospheres was further confirmed to be superior to that of Co-Ni nanosheets.(3)The Ni nanoaprticles were uniformly and firmly anchored on TiO2 nanobelts,where about 10%Ni atoms strongly bonds with the O atoms of TiO2 surfaces to form Ni-O-Ti active species.As an 'electron promoter',the obtained Ni-O-Ti species could effectively regulate the electron transfer of Mg-H systems,weaken the Mg-H bonds and promote their hydrogen storage properties.The hydrogen storage in this catalyzed system can be realized at room temperature,along with the onset desorption temperature reduced by about 200?.More importantly,an effective storage capacity of?4.5 wt%can be retained after 30th cycles under milder conditions.(4)The low-energy Mg-Zr-H coupling interfaces were prepared by two-steps methods of high-pressure ball-milling and isothemal treatment,in order to effectively improve their hydrogen storage properties.The obtained Mg-Zr-H systems exhibit rapid hydrogen sorption at lower temperatures,i.e.,the absorption can reach to saturation at 100 ? within 2 h and the onset desorption starts at?235 ? with reduced activation energy of?40 kJ mol-1.These enhancements can be attributed to the synergy of grain refinements,catalysis and interfacial coupling effects,where the Mg-Zr-H interfacial coupling effects play a key role.(5)The catalysis/interface coacted MgH2 systems were constructed by mechanical milling.As compared to single catalysis or interfacial effect,the MgH2 synergetic systems have a superior desorption where the onset and completing temperatures are about 215 and 330 ?,respectively.This originates from both kinetic and thermodynamic enhancements.Moreover,the MgH2 synergetic systems also exhibit a better cyclic performance that the capacity retention can be kept by 80%after 30th cycles under the milder ab-/desorption conditions. |
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