Prepration Of Porous Nickel And Its Improvement Effect On The Hydrogen Storage Properties Of NaAlH₄ And LiBH₄

Hydrogen is believed to be the most ideal secondary source because of its high calorific value,low environmental impact and abundant resources.However,the efficient storage and safe transportation of hydrogen are one of the factors that restrict its practical applications.Therefore,it is necessary to develop hydrogen storage materials with high volume or mass density of hydrogen.Based on the review of the research on complex hydrides,NiAl₃ and Mn₇₀Ni₃₀ alloys were used as the precursors,and two kinds of porous nickel?Raney Ni and np-Ni?were prepared using the method of dealloying.Then the NaAlH₄/Raney Ni?1:4?,Li BH₄/Raney Ni?1:5?and LiBH₄/np-Ni?1:5?hydrogen storage systems were constructed by wet-dipping method.Finally,the de-/rehydrogenation properties and mechanisms were analyzed by means of N2 adsorption-desorption?BET?,scanning electron microscope?SEM?,energy dispersive spectroscope?EDS?,X-ray diffraction?XRD?and Fourier transform infrared spectroscopy?FTIR?.Raney Ni was prepared by dealloying the Ni-Al₃ alloy with alkali.BET testing shows that the Raney Ni is a mesoporous material with a specific surface area of 105 m2/g.The NaAlH₄/Raney Ni?1:4?system starts to release hydrogen at about 110 °C with an ending dehydrogenation temperature of about 250 °C.The amount of hydrogen desorbed is about5.2 wt.%.Raney Ni has a strong catalytic effect on the NaAlH₄,reducing the binding energy of the Al-H bond,and thus the dehydrogenation property can be significantly improved.The dehydrogenation activation energy of the NaAlH₄/Raney Ni?1:4?system was determined to be 19.6 kJ/mol,which is much lower than the reported NaAlH₄@MC nano-confinement system with an activation energy of 46±5 kJ/mol.The researches on the rehydrogenation properties show that the reversible hydrogen storage capacity of the NaAlH₄/Raney Ni?1:4?system are enhanced with increasing temperature from 150 °C to250 °C.The second dehydrogenation amount of the system after rehydrogenation at 250 °C and 7 MPa is 4.1 wt.%.The researches on the LiBH₄/Raney Ni?1:5?system show that it starts to release hydrogen at about 60 °C and finishes dehydrogenation process before 440 °C,with about11.1 wt.% of hydrogen desorbed.Raney Ni has a strong catalytic effect,which can enhance the charge transfer between lithium ion and [BH₄]-,and then reduce the binding energy of the B-H bond and significantly improve the dehydrogenation property.The studies on the kinetic characteristics indicate that the dehydrogenation activation energy of the Li BH₄/Raney Ni?1:5?system is 21.4 kJ/mol,which is lower than the reported Li BH₄@CA@CoNiB nano-confinement system with an activation energy of 46 kJ/mol.After rehydrogenation at 450 °C and 8 MPa,the second dehydrogenation amounts of the system reaches 7.4 wt.%.The researches on the LiBH₄/Raney Ni-10 wt.% NbF₅ system shows that it has a lower desorption temperature than the Li BH₄/Raney Ni?1:5?system.Np-Ni was prepared by dealloying the Mn₇₀Ni₃₀ alloy with?NH₄?₂SO₄ solution.BET testing indicates that the np-Ni is a mesoporous material with a specific surface area of 155m2/g.The LiBH₄/np-Ni?1:5?system starts to release hydrogen at about 70 °C,and ends before 400 °C.The amount of hydrogen desorbed is about 11.9 wt.%.Np-Ni has a large specific surface area with a strong catalytic effect on Li BH₄.Thus the binding energy of the B-H bond can be reduced,which is beneficial to the improvement on the dehydrogenation property.The studies on the kinetic characteristics indicate that the dehydrogenation activation energy of the LiBH₄/np-Ni?1:5?system is 11.4 kJ/mol,which is much lower than the LiBH₄/Raney Ni?1:5?system with an activation energy of 21.4kJ/mol.The second dehydrogenation amount of the system is 8.2 wt.%,which is better than the Li BH₄/Raney Ni?1:5?system.