Microstructure And Properties Of V-Based Hydrogen Storage Alloys For Hydrogen Compression

With the increasing depletion of fossil energy sources worldwide,hydrogen energy is considered as an ideal new alternative energy source.Hydrogen compression technology is one of the key technologies for hydrogen energy applications.Metal hydride compressed hydrogen technology has received a lot of attention because of its safety,noiselessness,and the possibility of using low-quality waste heat.V-based hydrogen storage alloy is a promising material for hydrogen compression due to its fast hydrogen absorption and discharges kinetic performance and the ability to absorb and discharge hydrogen at room temperature.However,the drawbacks of V-based hydrogen storage alloys,such as high slope and hysteresis of hydrogen absorption and discharge plateau,seriously affect their practical applications.To obtain V-based alloys with excellent hydrogen compression performance,this thesis reduces the plateau slope and hysteresis of V-based alloys by elemental substitution of V₈₀Ti₂₀ alloy and selecting a suitable heat treatment process.Through detailed analysis of V-based alloys with different compositions and the organization and hydrogen storage properties of the alloys before and after heat treatment,the changes in hydrogen compression properties of V-based alloys with different compositions and the influence of heat treatment process on the organization and hydrogen storage properties of V-based alloys are studied,and the calculation equations of hydrogen compression properties are optimized,and the main results are obtained as follows.（1）Among V₈₀Ti₂₀,V₇₅Ti₂₅,V₇₅Ti₂₀Cr₅,V₇₅Ti₂₀Zr₅,V₇₅Ti₂₀Ni₅,and V₇₅Ti₂₀Mn₅ alloys,V₈₀Ti₂₀ alloy has the most hydrogen content,and the lowest plateau slope coefficient of 1.8 wt.%and 0.3,respectively.V₇₅Ti₂₀Cr₅ alloy has the smallest average pressure hysteresis coefficient of0.45,and has the best-integrated hydrogen compression performance,with the compression ratio,exhaust rate,and hydrogen compression efficiency of 1.75,5.50 L/min and 3.60%,respectively.（2）The hydrogen compression ratio calculation equation was optimized by introducing the platform slope coefficient and pressure hysteresis coefficient,and the exhaust rate of the hydrogen compression alloy was calculated using the Johnson-Mehl-Avrami-Kolomogorov（JMAK）model fitting.The results show that the accuracy of the results calculated by the optimized compression ratio formula increases,and the exhaust rate calculated using the JMAK model can accurately reflect the real exhaust rate of the alloy.The optimized hydrogen compression performance calculation formula shows that the hydrogen storage alloy used for the hydrogen compression system should have higher standard reaction enthalpy,larger hydrogen storage content,faster hydrogen absorption,discharge reaction rate,lower plateau slope,and hysteresis,and lower thermal conductivity.（3）There is obvious composition segregation in the central region of the molten V-based alloy,and the quenching heat treatment of the molten V₈₀Ti₂₀,V₇₅Ti₂₀Ni₅,and V₇₅Ti₂₀Mn₅ alloy samples after holding at 950℃and 1150℃for 6 h,respectively,can effectively eliminate the composition segregation,increase the reaction rate of hydrogen absorption and discharge,reduce the slope coefficient of the platform and pressure hysteresis coefficient,and thus improve the hydrogen compression performance of the alloy.The heat treatments at 1150℃and 1150℃can effectively eliminate the composition segregation,increase the reaction rate of hydrogen absorption and discharge,reduce the slope coefficient of the plateau and the pressure hysteresis coefficient,and thus improve the hydrogen compression performance of the alloy.The hydrogen compression ratio of the V₇₅Ti₂₀Ni₅ alloy after heat treatment at 1150℃was the most improved,with a hydrogen compression ratio of 0.53,which increased by 0.40 compared with that of the molten alloy.