Preparation Of Nanoporous Copper-nickel Alloy And Improvement Effect On The Hydrogen Ab-/desorption Properties Of Borohydrides

Hydrogen energy is considered as an ideal sustainable energy carrier in the future because of its abundant sources,high calorific value and environment friendly.The development of safe,portable,efficient and economical hydrogen preparation and storage technologies is the key for its wide application.In this dissertation,the nanoporous copper-nickel alloy（NP-（Cu,Ni））was successfully prepared by dealloying Mg-Cu-Ni alloy precursor,and LiBH₄ was loaded in the nano channel to improve its hydrogen ab-/desorption properties based on the synergistic nanoconfinement and catalytic effect.In addition,the Mg-Cu-Ni alloy precursor ball-milled followed by dealloying was used as the catalyst for hydrogen production of NaBH₄ hydrolysis for extending the application range of NP-（Cu,Ni）.X-ray diffraction（XRD）,Fourier transform infrared spectroscopy（FTIR）,Scanning electron microscopy（SEM）,Energy dispersive spectroscopy（EDS）and nitrogen adsorption and desorption（BET）were used to analysis the hydrogen ab-/desorption mechanism of borohydrides.The Mg-Cu-Ni alloy precursor was dealloyed by citric acid solution,and the obtained NP-（Cu,Ni）is composed of（Cu,Ni）solid solution.The LiBH₄ was filled into NP-（Cu,Ni）channels via wet impregnation.The NP-（Cu,Ni）has an excellent catalytic effect on the first hydrogen desorption of LiBH₄.The starting and ending hydrogen desorption temperatures of the LiBH₄/NP-（Cu,Ni）（1:5）system are 90 and 360°C,respectively,with a total hydrogen desorption amount of 13.4 wt.%.The dehydrogenation activation energy of LiBH₄/NP-（Cu,Ni）（1:5）system was determined to be 30.79 k J/mol,which is remarkably improved as compared with pure LiBH₄（E_a～180 k J/mol）.In order to avoid the influence of by-products such as BNi₂ and Li₂B₁₂H₁₂ in-situ generated on the reversibility of LiBH₄/NP-（Cu,Ni）（1:5）system,the hydrogenation was performed under 350°C and 8 MPa for 4 h.The hydrogen desorption amount is maintained 68%of the initial value after 10 cycles.The LiAlH₄ was further introduced into the LiBH₄/NP-（Cu,Ni）system in order to construct the reactive destabilization-nanoconfinement-catalytic system.The temperature dependence of dehydrogenation testing shows that the hydrogen desorption process of2LiBH₄+LiAlH₄/NP-（Cu,Ni）system can be divided into two steps.Among them,the initial hydrogen desorption temperature for step I is 130°C and the ending temperature for step II is 360°C with about 9.75 wt.%of total hydrogen desorbed.In addition,the hydrogen desorption activation energy of the 2LiBH₄+LiAlH₄/NP-（Cu,Ni）（1:5）system was remarkable decreased to be 44.63 k J/mol.No Al B₂ was formed during the hydrogen desorption process of LiAlH₄ and LiBH₄.While Al in-situ generated reacted with Cu to form Al₄Cu₉ that destroyed the original structure of the material,which leads to the increase of activation energy and decrease of catalytic property.The hydrogen desorption amount remains 80%of the initial value for the 2LiBH₄+LiAlH₄/NP-（Cu,Ni）（1:5）system after 10cycles under the hydrogenation conditions of 300°C and 8 MPa for 4 h.M-NP-（Cu,Ni）was prepared by ball-milling followed by dealloying the precursor alloy.The results show that M-NP-（Cu,Ni）has excellent catalytic effect on the hydrolysis of NaBH₄ solution.It can be completely hydrolysis within 80 s with the dehydrogenation rate of hydrolysis reaching 446.65 m L·min^-1·g^-1 under the condition of 1.2 mol/L NaOH solution,1 wt.%NaBH₄ and 5 wt.%M-NP-（Cu,Ni）at 25°C.The excellent catalytic property of M-NP-（Cu,Ni）can be attributed to its higher specific surface area which brings more active sites to reduce the binding energy of B-H bond.The apparent dehydrogenation activation energy of the NaBH₄/M-NP-（Cu,Ni）system was determined to be 32.84 k J·mol^-1.In addition,the catalytic activity of M-NP-（Cu,Ni）remains 65%of the initial value after 5 cycles.