Theoretical Study On Phase Transition And Thermodynamic Properties Of Borohydride

The rapid development of human society and economy is inseparable from a variety of huge and efficient energy and the production machine driven by it.Therefore,the exploration of a renewable and safe and pollution-free energy form is an indispensable and necessary condition for the continuous development of social productivity and the eventual realization of communism.Among the various emerging energy sources,hydrogen energy has become one of the future energy sources with the greatest development potential due to its advantages of high specific energy,recyclability and no additional pollution to the environment.However,due to the technical problems of hydrogen storage and transportation,there are still great difficulties in the development of equipment with hydrogen as energy storage medium.However,due to the advantages of high hydrogen storage capacity,wide and cheap sources of synthetic raw materials,convenient transportation and storage,the coordination borohydride of alkali metals has aroused the enthusiasm of many researchers for its application in practical engineering production.In this background,this paper USES the method based on first principles density functional theory including boron sodium hydride of boron,potassium,boron hydride,lithium hydride thermodynamic calculation and analysis with the electrical properties,as well as the various properties of doped after was calculated,and its mixed with various properties on the basis of the comparison,the size of both the microscopic mechanism of nature of these differences are discussed.The research results show that:(1)the rotational energy barrier of borohydride tetrahedron increases with the increase of external pressure,which makes it more difficult to form borohydride high-temperature disordered phase and the phase transition temperature increases accordingly.Therefore,the phase transition temperature of borohydride is inversely proportional to its phase transition pressure.(2)the radius of metal ions in borohydride also affects the rotational energy barrier of borohydride tetrahedron.The larger the radius of metal ions is,the greater the hindrance to the rotation of borohydride tetrahedron will be,so the phase transition pressure required by the crystal will be lower.(3)the entropy of the high-temperature phase and the low-temperature phase of lithium borohydride tends to be consistent with the increase of doping concentration.Therefore,the phase transition temperature of the crystal will decrease with the increase of doping concentration.(4)the band gap size of lithium borohydride crystal will decrease with the increase of doping concentration,making it easier for the conduction band to stimulate more carriers,so the conductivity of the crystal will increase with the increase of doping concentration.