Synthesis And Application Of Inorganic Amide For Hydrogen Storage And Ionic Conductor

The development and application of hydrogen energy,solar energy,wind energy and other clean secondary energies have been widely concerned.However,application of these energies is limited by the lack of safe and efficient storage and transportation technologies.Amide-hydride composite is one of the solid hydrogen storage materials with high application potential,but its re/dehydrogenation kinetics need further optimization.Inorganic amide has also been reported as solid electrolyte in all solid-state batteries with high safety.The hydrogen storage and kinetic performance of K₂Mn（NH₂）₄-8Li H and ionic conduction of KNH₂ were studied in this thesis.The main contents are as follows:K₂Mn（NH₂）₄was synthesized by grinding metal K,Mn and ammonia.The hydrogen storage performance of K₂Mn（NH₂）₄-8Li H was measured.It can release more than 6.0 wt%H₂ in an open system with a little of by-product ammonia.In a closed system,it is able to reversibly store more than 3.0 wt%of hydrogen（re-dehydrogenation and dehydrogenation temperatures was 300℃and 375℃,respectively）.The dehydrogenated K₂Mn（NH₂）₄-8Li H sample is one of the fastest hydrogenated amide-hydride composites,which has a absorption rate of about 1wt%/min at 230℃,and 50 bar H₂.In situ SR-PXD technology was used to explore the reaction processes of K₂Mn（NH₂）₄-8Li H during re-dehydrogenation and dehydrogenation.It is revealed that an"unknown"phase is appeared and disappeared during the re/dehydrogenation cycle,which is related to the fast hydrogen absorption.In principle,improvement of mass transfer in complex hydrides is an efficient way to enhance the kinetic properties.The ultra-fast hydrogenation rate indicates high ionic transportations in this material.Under the guideline of ultra-fast hydrogenation,a new type of potassium solid ion conductor material KNH₂ was developed.KNH₂,was synthesized by reacting metal K and ammonia.It is a K⁺conductor with an ionic conductivity of 9.84×10^-7 S cm^-1 at 40℃,and increasing to 4.84×10^-5 S cm^-1 at 150℃.The ionic conductivity and conduction ability of KNH₂ can be improved by mechanical ball milling.The ionic conductivity of the ball milling treated KNH₂(V₁₅₀T₁₀,ball milling 150 rpm for 10 h)is 4.39×10^-7 S cm^-1 at room temperature.And the conductivity is increased to1.39×10^-6 S cm^-1 and 3.56×10^-4 S cm^-1 at 40℃and 150℃,which are 140 and 7 times higher than that of the pure KNH₂.The increasement of the ionic conductivity is due to the increasing of defects number in the crystal lattice of KNH₂ which were introduced by the ball milling process.Apart from KNH₂,the ionic conductivity of other alkali metal amides such as Li NH₂ and Na NH₂can also been improved by ball milling.In addition,ionic conductivity of polycationic（alkali metal ion）amide mixtures（Li NH₂,Na NH₂,KNH₂）has been studied as well.Na NH₂-KNH₂ mixture has the highest ionic conductivity of 3.67×10^-2 S cm^-1 at 110℃.