First-Principles Study Of The K-B-H Hydrogen Storage Materials

The whole world is faced with energy crisis, while hydrogen is the most popular green energy. Faced with the difficulty of storaging hydrogen, we must study the development of superior nature of hydrogen storage materials. First-principles based on density functional theory （DFT） has become the most extensive and effective tool to study hydrogen storage materials. Scientists have made a thorough research in this area. Under such background we select the K-B-H Department as the main object of our study. Specifically, we conducted a study of the following two aspects.First, based on the density functional theory （DFT） plane wave pseudopotential （PBE）, lattice parameters, electronic structure and lattice vibrations, the density of statesstudy of the K2B12H12are studied systematically, of using the generalized gradient approximation. The study shows that K2B12H12is composed of K+and [B12H12]2-, and they are combined in the form of ionic bond. They are interaction between the B and H atoms through the form of a covalent bond in [B12H12]2-ion. From the phonon density of states of the lattice vibration, we can draw the result that the bond energy is relatively low, and is easily broken.The bond energy between B atoms and H atoms in the [B₁₂H₁₂]^2-ionic groups can be larger andfracture requires a higher energy, which requires a hightemperature hydrogen desorption for K₂B₁₂H₁₂. we also predictedthe stability of KBH4from theory, and the crystal structure, theelectronic structure and the thermodynamic reaction of KBH4arealso studied with the density functionl theory. The calculation ofcrystal structure and electronic structure show that KBH4iscomposed of K⁺and [BH4]-, and they are combined in the form ofionic bond. They are interaction between the B and H atoms throughthe form of a covalent bond in [BH4]-ion cluster.The calculation ofthe density of the electronic states show that the energy gap of theγ-KBH4is7.8eV, and γ-KBH4is insulator. We also calculate theenthalpy change, entropy, and decomposition temperature of tworeaction. The calculations show that, if the K₂B₁₂H₁₂is used as anintermediate product, it is useful to the decomposition reaction ofKBH4.Second, using density functional theory, we calculateddescribed NaK（BH₄）₂crystal structure and thermodynamics of thereaction. Through analyzing the electronic structures of theNaK（BH₄）₂, the metal cations and the ionic groups in the NaK（BH₄）₂are into the role of the ionic bond, and the B and H atoms in the ionicgroup [BH4]-was covalently key. The density of states shows that,NaK（BH₄）₂is an insulator, and the energy gap is6.1eV. We havecome to the conclusion that if the low vibration entropy XnB₁₂H₁₂（X=lithium, potassium, calcium） is used as an intermediate product, itis useful to the reaction of NaK（BH₄）₂.I hope our research can provide some theoretical guidance for experimental studies of hydrogen storage materials.