The Mg(NH_(2))_(2)-2LiH composite system is a promising vehicle-mounted hydrogen sto rage material,but its application is limited due to serious thermodynamic and kinetic barriers.Adding additives can effectively opti...The Mg(NH_(2))_(2)-2LiH composite system is a promising vehicle-mounted hydrogen sto rage material,but its application is limited due to serious thermodynamic and kinetic barriers.Adding additives can effectively optimize their hydrogen absorption and desorption kinetics and thermodynamic performance.In this work the comprehensive hydrogen storage performance of Mg(NH_(2))_(2)-2LiH with extremely small nano rare earth borides is improved,and a series of characterization methods and density functional theory(DFT)calculation systems was combined to study its hydrogen storage improvement mechanism.The research results show that the method of adding 5 wt%molten salt to prepare nano CeB_(6)(24.5 nm)can significantly reduce the initial hydrogen absorption/release temperature of Mg(NH_(2))_(2)-2LiH from 110/130to 45/90℃,inhibit the generation of ammonia by-products,and improve hydrogen purity.Under lowtemperature hydrogen absorption conditions at 120℃,the improved sample can absorb 2.81 wt%hydrogen gas,with a hydrogen absorption capacity more than 3.5 times of the unmodified sample.The amount of hydrogen released at 150℃reaches 3.35 wt%,which is more than twice that of the pristine sample,demonstrating excellent hydrogen absorption and release kinetics performance.After 10 consecutive hydrogen cycles,4.64 wt%hydrogen can still be released,and the cycle retention rate can be increased from 85%before improvement to nearly 100%,demonstrating good reversibility.Mechanism studies show that nano CeB_(6)can effectively weaken the Mg-N and N-H bonds of Mg(NH_(2))_(2)and inhibit the polycrystalline transformation of the hydrogen evolution product Li_(2)MgN_(2)H_(2)at high temperatures.It can also provide nucleation active sites for hydrogen absorption and desorption in the material,making the system possess superior hydrogen absorption and desorption performance and cycling stability.This study provides new insights into the role of rare earth borides in Mg(NH_(2))_(2)-2LiH hydrogen storage materials,both experimentally and theoretically.展开更多
基金Project supported by the National Natural Science Foundation of China(51971199,51771171)。
文摘The Mg(NH_(2))_(2)-2LiH composite system is a promising vehicle-mounted hydrogen sto rage material,but its application is limited due to serious thermodynamic and kinetic barriers.Adding additives can effectively optimize their hydrogen absorption and desorption kinetics and thermodynamic performance.In this work the comprehensive hydrogen storage performance of Mg(NH_(2))_(2)-2LiH with extremely small nano rare earth borides is improved,and a series of characterization methods and density functional theory(DFT)calculation systems was combined to study its hydrogen storage improvement mechanism.The research results show that the method of adding 5 wt%molten salt to prepare nano CeB_(6)(24.5 nm)can significantly reduce the initial hydrogen absorption/release temperature of Mg(NH_(2))_(2)-2LiH from 110/130to 45/90℃,inhibit the generation of ammonia by-products,and improve hydrogen purity.Under lowtemperature hydrogen absorption conditions at 120℃,the improved sample can absorb 2.81 wt%hydrogen gas,with a hydrogen absorption capacity more than 3.5 times of the unmodified sample.The amount of hydrogen released at 150℃reaches 3.35 wt%,which is more than twice that of the pristine sample,demonstrating excellent hydrogen absorption and release kinetics performance.After 10 consecutive hydrogen cycles,4.64 wt%hydrogen can still be released,and the cycle retention rate can be increased from 85%before improvement to nearly 100%,demonstrating good reversibility.Mechanism studies show that nano CeB_(6)can effectively weaken the Mg-N and N-H bonds of Mg(NH_(2))_(2)and inhibit the polycrystalline transformation of the hydrogen evolution product Li_(2)MgN_(2)H_(2)at high temperatures.It can also provide nucleation active sites for hydrogen absorption and desorption in the material,making the system possess superior hydrogen absorption and desorption performance and cycling stability.This study provides new insights into the role of rare earth borides in Mg(NH_(2))_(2)-2LiH hydrogen storage materials,both experimentally and theoretically.
