An Investigation On Phase Structure And Hydrogen Storage Properties Of Mechanical La₂mg₁₇-Ni-Nbf₅/Tif₃Composite Material

Based on the review of the research and development of the Mg-based hydrogen storagealloys, La₂Mg₁₇hydrogen storage alloy was selected as the study object of the work due to itshigher storage capacity than Mg-Ni system alloy. In order to achieve well La₂Mg₁₇alloygaseous and electrochemical absorption/desorption reversibly by the ball-milling methond inLa₂Mg₁₇+xwt%Ni（x=50,100,150,₂00）+ywt%NbF₅/TiF₃（y=0,3,5） proportion to obtainingamorphous composites. By means of XRD, SEM analyses and the electrochemical testmethods including the galvanostatic charge/discharge, EIS, linear polarization, potential-stepmethod etc, the microstructure and electrochemical properties influence on the ball-milled Nipowder, catalyst and milling time composites were systematically studied. The La₂Mg₁₇composite alloy of hydriding kinetics properties were measured by automatically controlledSieverts apparatus, analysis of the Ni powder, catalyst and milling time controlling on gaseoushydrogen storage composites, and this process of the reaction mechanism is further studied.The study of the influence of Ni powder, catalyst and ball-milling time on themicrostructure and gaseous hydrogen absorption/desorption properties of La₂Mg₁₇compositealloys revealed that ball-milling can make excellent La₂Mg₁₇composites hydrogenation/dehydrogenation invertiblly. The maximum hydrogen absorption capacity of amorphous150wt%Ni composites is7.₂9wt%H₂, respectively, the maximum hydrogen desorptioncapacity of amorphous150wt%Ni composites is₂.31wt%H₂at1MPa. It is found that ball-milling is advantageous for the formation of amorphous structure, thus leading to theimprovement of thermodynamic and kinetic properties of the ball-milled composites. Thecomposites kinetics of gaseous hydrogen absorption properties is improve significantly.Besides, the introduction of dynamic model is discussed gaseous hydrogen on the experimentaldata to estimate the occurrence of various stages of hydrogenation time. Required for thecharacterization of gaseous hydrogen storage materials study provides a new target parameters.The study of the influence of Ni powder, catalyst and ball-milling time on themicrostructure and electrochemical properties of La₂Mg₁₇composite revealed that ball-millingcan improve the amorphization degree, and dramatically ameliroate the electrochemicalreaction of the composite alloy dynamics. This method can make favorable La₂Mg₁₇composites charge/discharge reversibly at room temperature. The maximum discharge capacityof amorphous150wt%Ni composites is787.07and775.16mAh/g when added TiF₃and NbF₅, respectively. The discharge capacity of the amorphous composite is influenced by theamorphization degree and particle size. But both of them are closely related with Ni powderaddition and milling time. The results indicate that the addition of small amounts of metalfluoride can improve the amorphization degree of the composites, thus leading to theimprovement of discharge capacity and high-rate discharge ability. Due to metal fluoride causethe decrease of activation energy and electrochemical reaction resistance and then the increaseof exchange current density. But the addition of metal fluoride has little effete on the cyclingstability. In addition, impedance spectra of alloy （EIS） fitting, polarization current calculation,the introduction of hydrogen diffusion kinetics model, the electrochemical hydrogen storagemechanism are analyzed systematically in detail.