Hydrogen Storage MaterialsHydrogen Storage Materials1 1教教 学学 内内 容容 1.氢能技术及储氢材料的基本特征2学时 2.稀土系储氢材料4学时 3.镁系储氢材料2学时 4.钛系、锆系储氢材料2学时 5.钒系储氢材料2学时 6.储氢材料的热力学性质2学时 7.储氢材料的氢化反应动力学2学时 8.储氢材料及其氢化物的晶体结构2学时 9.储氢材料的制备技术2学时 10. 氢化物法的氢储存与贮运2学时 11. 氢化物法的氢净化与压缩2学时 12. 氢化物法的氢气回收和同位素分离2学时 13. 氢化物法蓄热及热泵2学时 14. 储氢材料的电化学应用2学时2 2Thermodynamics of Hydrogen Storage Alloys Thermodynamics of Hydrogen Storage Alloys Lecture VILecture VI3 31.1 Introduction 1) P-C-T curves ( P-C isotherms) Pressure v There are three regions: region : solid solution;I I . . Equilibrium of M-H systems Equilibrium of M-H systems (+) region: double phasesplateau; region: hydride phase.CompositionTemperature 4 42) Gibbs phase rule F F = = C C P P + 2 + 2 Where : F is the freeness of system; C is the component number of system (M and H);P is the phase number. For region: F = C P + 2 = 2 2 + 2 = 2, so, at fixed T, all of P and C are variable; For (+) region: F = C P + 2 = 2 3 + 2 = 1, so, at fixed T, only C is variable and P is invariable; For region: F = C P + 2 = 2 2 + 2 = 2, so, at fixed T, all of P and C are variable; I I . . Equilibrium of M-H systems Equilibrium of M-H systems 5 51.2 (or ) solid solution region Assuming that the system is ideal, and at equilibrium: I I . . Equilibrium of M-H systems Equilibrium of M-H systems 6 6v There is a direct proportion between the solid solubility Hs.s. and PH2 v Mono-phase solid solution region is unimportant for hydrogen storage system. 1.2 1.2 (or (or ) solid solution region ) solid solution region 7 71.3 ( + ) region 1) Vant-Hoff equationq The saturated solid solution phase absorb hydrogen and form phase hydride through phase transformation: I I . . Equilibrium of M-H systems Equilibrium of M-H systems 8 81.3 (1.3 ( + + ) region ) region 9 91.3 (1.3 ( + + ) region ) region Where : PH2 is the hydrogen equilibrium pressure (atm);H is the formation enthalpy of hydride;S is the entropy of a transformation;R is the gas constant ( R = 8.31441 J/mol.K ).v There is a precondition: AssumeG,H andS are invariable in (+) region. 1010v slope H v As 1/T0, intercept S 1.3 (1.3 ( + + ) region ) region La2Ni4 (3f) LaNi3 (12o, 12n) Ni4 (4h) 3.1 3.1 LaNi LaNi5 5based based HSAs HSAs72726) The occupation sites of M in LaNi5-xMx (M=Al, Mn, Co, Si). q M atom may occupy either NiI(2c) site or NiII(3g) site; q As the M has a larger atomic radius, M atom occupies mainly a NiII(3g) site due to its large space. 3.1 3.1 LaNi LaNi5 5based based HSAs HSAs7373Mn: occupy NiII(3g) and NiI(2c) sites;3.1 3.1 LaNi LaNi5 5based based HSAs HSAsSuch as : as x = 0.4, 82% Co NiII(3g) sites, 18% Co NiI(2c) sites; as x = 1.0, 75% Co NiII(3g) sites, 25% Co NiI(2c) sites.Al: occupy only NiII(3g) sites as x rB in AB2; Ideally, rA/rB = 1.225; Really, rA/rB = 1.051.68.(2) Electronic structure (i) Electronic density (E.D., 电子浓度) 79793.2 AB3.2 AB2 2type Laves phase type Laves phase HSAs HSAs (ii) Average number of outer electrons (ANOE, 平均外层电子数V ) vThe phase type of Zr- or Ti-based alloys are related to ANOE;vVegards law: VAxB1-x = xVA + (1-x)VBFor example: ZrV0.5Ni1.5, outer electron: Zr4, V5, Ni10 . VANOE = (14+0.55+1.510)/3 7.16 So, this alloy tends to form a C15 type Laves main phase. 80803.2 AB3.2 AB2 2type Laves phase type Laves phase HSAs HSAs (3) Interstice site for H stored vThere is only tetrahedral interstice sites in Laves phase. 8181T.I.S. number of per Laves phase cell vTotal: 17 T.I.S. Per Laves phase cell.3.2 AB3.2 AB2 2type Laves phase type Laves phase HSAs HSAs vThe distance of two tetrahedral interstice sites with coplanarity (共面) is 0.16 nm;vThe distance of two tetrahedral interstice sites without coplanarity is over 0.22 nm.8282(4) Maximum capacity of H in Laves phase cell .v Switendicks viewpoint : the minimum distance of H-H for stable hydride is over 0.21 nm;3.2 AB3.2 AB2 2type Laves phase type Laves phase HSAs HSAs v The Shoemakers principle of filling incompatibly: two tetrahedral interstice sites with coplanarity cannot be synchronously occupied by two H atoms.v D.G. Westlakes criterion: ri.s. 0.04 nm; rH-H 0.21 nm.8383vFrom above principles, the maximum capacity of H absorption in per AB2 cell can be calculated: For C15, 6 H / AB2For C14, (19/3) H / AB2H atom occupies firstly in T.I.S. composed of more A atoms;3.2 AB3.2 AB2 2type Laves phase type Laves phase HSAs HSAs T.I.S. of B4 cannot absorb almost hydrogen.Laves phase has more T.I.S., so Laves alloys have high capacity.Such as C = 1.8 wt.%