Hydrogen Storage Performance And Mechanisms Study Of Magnesium Based Alloy

Magnesium and its derived alloys are considered to be the most promising hydrogen storage materials because of their large storage capacity,light weight,and low cost.However,higher hydrogenation temperatures and slow rates of hydrogen absorption and desorption seriously affect their practical application.In recent years,studies have found that by adding Y element to Mg-Ni alloys,the formed Mg-Ni-Y alloy contains a special LPSO structure,which is a stacking fault with densely distributed Ni and Y atoms.These faults can be used as fast channels for the transport of hydrogen atoms.As a result,the kinetic properties of the alloy have been significantly improved,but the problem of higher hydrogenation temperature has not yet been solved.Therefore,it is urgent to find a novel and simple method to reduce the hydrogen release temperature of magnesium aloys.In this study,the as-cast Mg₁₂NiY alloy was prepared by suspension induction melting method first.Through ultra-high pressure treatment on the as-cast alloy at different temperatures,the Mg-Ni-Y alloy with superfine LPSO structure was obtained.The composition,microstructure,crystal structure,and hydrogen storage properties of different alloys were studied.Moreover,the improvement of hydrogen storage performance and its mechanism were analyzed in depth.In addition,this paper also combines physisorption and chemisorption.Based on the metal magnesium and MIL-101that with high hydrogen storage capacity,a one-step reduction method is used to prepare the Mg/MIL-101 composite material that with physisorption and chemisorption at the same time.Then explore the hydrogen storage performance under different conditions by regulating its synthesis method.The experimental results showed that the volume fraction of LPSO phase in Mg₁₂NiY alloy increases obviously after ultrahigh pressure treatment,and the phase distribution in the alloy is more compact and uniform than the as-cast alloy.The test results of hydrogen storage performance indicated that the hydrogen storage performance of Mg₁₂NiY alloy can be effectively improved by ultrahigh pressure treatment technology.In particular,the activation performance,hydrogen storage capacity and hydrogen absorption and release kinetics of Mg₁₂NiY alloys can be significantly improved.In addition,ultra-high pressure technology can also reduce the initial hydrogenation temperature of the alloy,and improve the hysteresis of the hydrogen storage alloy during hydrogen absorption and desorption.The results of the Mg/MIL-101 system showed that the optimal synthesis conditions for Mg/MIL-101 composites are as follows:hydrothermal reaction at 220°C for 24 h,purification with NH₄F solution,the concentration of doped MgCl₂ is 0.5 mol/L.Moreover,its hydrogen storage performance has been improved compared to the MIL-101.In this study,the microstructure of the material and the special structure of the LPSO phase are used to deeply analyze the improvement of the hydrogen storage performance of the alloy and its mechanism.The following conclusions are drawn:the special long-period stacking structure and the stacking direction of the 18R type LPSO make the diffusion activation energy of H atom in the structure is very low.After the ultrahigh pressure treatment,the volume fraction of LPSO phase increased significantly;the increase of the phase interface is beneficial to the activation;the more even distribution of the elements is beneficial to the in-situ catalysis of YH₂ and Mg₂Ni.In summary,the hydrogen storage performance of Mg₁₂NiY alloys can be significantly improved through the ultrahigh pressure treatment technology.