HYDROGEN IN METALS / METALHYDRIDES Andreas Zttel CONTENTS 1) - PowerPoint PPT Presentation

HYDROGEN IN METALS / METALHYDRIDES Andreas Züttel CONTENTS 1) Hydrogen interaction with surfaces 2) Hydrides 3) Stability and hydrogen density 4) Complex hydrides

HYDROGEN DENSITY 200 Hydrogen density [kg/m 3 ] 150 NH 3 100 carbon liq. hydro- liq. natural hydrates carbons gas 50 liq. H 2 comp. 0 H 2 gas 0 10 20 30 Hydrogen density [kg H 2 / 100kg storage material] Andreas Züttel, Switzerland, 17.07.14

INTERACTION OF GASES WITH SURFACES G H T S Δ = Δ − ⋅ Δ Ref: W. Göpel, B. Kühnemann, Z. Phys. Chem. N.F. 122 (1980), p. 75

CHEMISORPTION OF GASES ON METAL SURFACES Δ E chem ≈ 0.25 eV Ref: M. Henzler, W. Göpel, „Oberflächenphysik des Festkörpers � , Teubner Studienbücher Physik, B. G. Teubner Stuttgart 1991, p. 474

LENNARD-JONES POTENTIAL Ref.: J. E. Lennard-Jones, Trans. Faraday Soc. 28 (1932), pp. 333. L. Schlapbach, Chapter 1, L. Schlapbach (Ed.) in Intermetallic Compounds I, Springer Series Topics in Applied Physics, Vol. 63, Springer–Verlag, 1988, p. 10.

BINARY HYDRIDES Ref.: Gottfried Brendel, � Kapitel: Hydride � , Ullmanns Encyklopädie der technischen Chemie, 4. neubearbeitete und erweiterte Auflage, Band 13 (1977), pp. 109-133, Verlag Chemie Weinheim New York Andreas Züttel, Switzerland, 17.07.14 6

DISCOVERY OF HYDROGEN ABSORPTION IN METALS British chemist often referred to as � the father of colloid chemistry. � Educated in Scotland, Graham persisted in becoming a chemist, though his fat- her disap- proved and with- drew his support. He then made his living by writing and teaching. He Thomas GRAHAM , born Dec. was a professor at a school in 20, 1805, Glasgow, Scot., died Edinburgh (1830–37) and at Sept. 11, 1869, London, Eng. University College, London (1837– 55), and was master of the mint (1855–69). In his final paper he described palladium hydride , the first known instance of a solid compound formed from a metal and a gas. Ref.: Thomas Graham„On the Occlusion of Hydrogen Gas by Metals“, Proc. Royal Soc. 16 (1868), pp. 422

HYDROGEN ABSORPTION IN METALS Ph. Mauron, M. Bielmann, EMPA, Switzerland 8

HYDROGEN ABSORPTION IN METALS ZrMn 1.5 0 sec (vacuum) 5 sec (8 bar H 2 ) 15 sec (8 bar H 2 ) 8 sec (8 bar H 2 ) 20 sec (8 bar H 2 ) 30 sec (7 bar H 2 ) 45 sec (6 bar H 2 ) 60 sec (5 bar H 2 ) 9

HYDROGEN IN AND ON PALLADIUM After exposing Pd(111) at 115 K to equal THERMO DESORPTION doses of H 2 and D 2 a much stronger SPECTROSCOPY desorption of α -H than α -D is observed apparently due to faster H than D absorption into α -states. α β α : chemisorbed hydrogen at the surface β : interstitial hydrogen Only minor HD desorption was ob- served. Apparently the gas which was Ref.: G. E. Godowski, R. H. Stulen, T. E. Felter, J. dosed second bypassed the chemi- Vac. Sci. Technology A5 (1987), pp. 1103 sorption state.

HYDROGEN IN AND ON PALLADIUM

THERMODYNAMICS OF HYDRIDES Δ H M + n/2 H 2 → MH n S 0 (MH n ) ≈ S 0 (M) M + n/2 H 2 → Δ S 0 ≈ -S 0 (H 2 ) H 2 Δ H f S 0 (H 2 ) = 130 JK -1 mol -1 MH n Δ H 0 = 2/n · Δ H f = 0 = 0 2 n & # 0 0 ( ) 0 ( ) 0 ( ) ! H H MH H M H H Δ = ⋅ Δ − Δ − Δ $ n 2 n 2 % " 2 n & # 0 0 ( ) 0 ( ) 0 ( ) ! S S MH S M S H Δ = ⋅ − − $ n 2 n 2 % " ≈ 0 Andreas Züttel, IfRES (2005) 12

HYDROGEN IN METALS EFFECTIVE MEDIUM THEORY METAL n H r Jens Norskov Ref.: P. Nordlander, J. K. Norskov, and F. Besenbacher, J. Phys. F. Metal Phys. 16:9 (1986), pp. 1161-1171, J.K. Norskov and F. Besenbacher, J. of the Less-Common Metals 130 (1987), pp. 475-490

HEAT OF SOLUTION Andreas Züttel, Switzerland, 17.07.14 1 4

LATTICE GAS E N N = ε + ε H o HH ε 0 ε The free energy F = U - T·S is N : total number of sites N H : number of H N N ε + ε " # F kT ln exp H o HH ∑ : H binding energy = − − ε 0 % & kT ' ( N HH : number of nearest neighbour H-pairs : H-H pair interaction energy ε Ref. Ronald Griessen, VU Amsterdam, NL Hemmes H, Salomons E, Griessen R, Sänger P, Driessen A., Phys Rev B Condens Matter. (1989);39(15):10606-10613.

ISOTHERM Δ G Δ H Δ S p c H 1 k T ln n c 1 T k ln ⋅ ⋅ ⋅ = ε + ε ⋅ ⋅ − ε + ⋅ ⋅ 0 H b 2 2 p ( T ) 1 c − 0 H Ronald Griessen Solubility (Sieverts) 1 p k T ln k T ln c ⋅ ⋅ ⋅ ≅ ⋅ ⋅ H 2 p ( T ) 0 p 0 c 0 → → H Plateau (Maxwell) p dis k T ln 2 n ⋅ ⋅ = ⋅ ε + ε ⋅ − ε 0 b p ( T ) 0 Coexistence curve c 1 = k T ln i n ( c ) 0 ⋅ ⋅ + ε ⋅ ⋅ − i 2 1 c − i Ref. Ronald Griessen, VU Amsterdam, NL

HYDROGEN ABSORPTION IN METALS S Δ R H Δ − R 0 0 1 p 1 p p H S ' $ ' $ ) & Δ Δ ( ) ( ) ln k T ln c ln k T ln c ln % " % " ' $ = ⋅ ⋅ = ⋅ ⋅ = − + % " % " ' $ H H 2 p 2 p p R T R ⋅ & # & # ( % 0 0 0 α -Phase: Solid Solution β -Phase: Hydride Phase MH x (0 < x < 0.1) MH x x = {1, 2, 3, … } H H, Δ V/V = k · c H H H Andreas Züttel, Switzerland, 17.07.14 1 7

STABILITY OF HYDRIDES: VAN’T HOFF PLOT T dec

THERMODYNAMICS OF HYDRIDES Δ H x A + y B + n/2 H 2 → A x B y + n/2 H 2 → A x B y H n x A + y B + n/2 H 2 S 0 (A x B y H n ) ≥ S 0 (A x B y ) → (Δ S 0 ( ≤( -S 0 (H 2 ) ( Δ H f,M S 0 (H 2 ) = 130 JK -1 mol -1 A x B y + n/2 H 2 H 2 Δ H f,H 2 n & # ( ) ( ) 0 0 0 0 ( ) ! H H A B H H A B H H Δ = ⋅ Δ − Δ − Δ $ x y n x y 2 n 2 % " 2 n & # ( ) ( ) A x B y H n 0 0 0 0 ( ) ! S S A B H S A B S H Δ = ⋅ − − $ x y n x y 2 n 2 % " Δ H 0 = 2/n · ( Δ H f,H - Δ H f,M ) Andreas Züttel, IfRES (2005) 19

ELECTRONIC STRUCTURE Bandstructure of LaNi 5 and LaNi 5 H 7 1) Lattice expansion reduces the band- width . 2) Attractive potential of the proton affects the metal states and leads to the metal- hydrogen band 5 to 8 eV below E F . 3) The H-H interaction results in new features in the lower part of the density of states for systems with more than one H atom per unit cell. 4) An upwards shift of E F results from the balance between the additional electrons brought in by hydrogen and the number of new states below E F . The balance between the ‘ exothermic ’ lowering of occupied states and the ‘ endothermic ’ upwards shift of E F d e t e r m i n e s t h e s t a b i l i t y o f t h e metalhydride. Ref.: L. Schlapbach, F. Meli, and A. Züttel, Chap. 21: “Intermetallic Hydrides and their Applications” in Intermetallic Compounds: Vol. 2, Practice, J. H. Westbrook and R. L. Fleischer (1994) John Wiley & Sons Ltd. Andreas Züttel, Switzerland, 17.07.14 2 0

BINDING ENERGY E F antibonding E noble metal E F Energy transition metal Adsorbate level bonding E F d H s s, p Ref.: Hammer B; Norskov J K, “Why Gold is the Noblest of all the Metals”, Nature 376, (1995), pp. 238-240 DoS

SEMI-EMPIRICAL MODEL FOR THE STABILITY The Local Band-Structure Model 4 − H a E W R b Δ = ⋅ Δ ⋅ ⋅ + ∑ j ∞ a = 18.6 kJ · mol -1 HÅ 4 eV -3/2 j b = -90 kJ · mol -1 H W Δ E R j Ref.: R. Griessen, Phys. Rev. B 38 (1988), pp.3690-3698 and V.L. Moruzzi, J. F. Janak, A.R. Williams, „Calculated Electronic Properties of Metals � , Pergamon, New York (1978) Andreas Züttel, Switzerland, 17.07.14 2 2

EMPIRICAL MODELS: STABILITY 1) Reversed stability (global) Δ H(AB n H 2m ) = Δ H(AH m ) + Δ H(B n H m ) - (1-F) · Δ H(AB n ) Miedema Model Ref.: H.H. Van Mal, K.H.J. Buschow and A.R. Miedema, J. Less-Common Met. 35 (1974), pp. 65 2) Imaginary binary hydrides (local) A m B n + xH → (A m B n H x ) interstitial site Δ H([A a B b ]H) = Δ H(A m H x · a/(a+b) ) + Δ H(B n H x · b/(a+b) ) binary hydrides Ref.: I. Jacob, J.M. Bloch, D. Shaltiel and D. Davidov, Solid State Comm. 35 (1980), pp. 155.

INTERSTITIAL SITES IN METAL HYDRIDES HYDROGEN HYDROGEN ON ON TETRAHEDRAL SITES OCTAHEDRAL SITES Ref: J. J. Reilly, G. D. Sandrock, � Metallhydride als Wasserstoff-Speicher � , Spektrum der Wissenschaften (April 1980), pp. 53-59 Andreas Züttel, Switzerland, 17.07.14 2 4

FAMILIES OF HYDRIDE FORMING INTERMETALLICS Intermetallic Prototype Structure compound AB 5 LaNi 5 Haucke phases, hexagonal AB 2 ZrV 2 , ZrMn 2 , TiMn 2 Laves phase, hexagonal or cubic AB 3 CeNi 3 , YFe 3 hexagonal, PuNi 3 -typ A 2 B 7 Y 2 Ni 7 , Th 2 Fe 7 hexagonal, Ce 2 Ni 7 -typ A 6 B 23 Y 6 Fe 23 cubic, Th 6 Mn 23 -typ AB TiFe, ZrNi cubic, CsCl- or CrB-typ A 2 B Mg 2 Ni, Ti 2 Ni cubic, MoSi 2 - or Ti 2 Ni-typ 25 Andreas Züttel, University of Fribourg, 15.12.2002

BODY CENTERED CUBIC SOLID SOLUTION ALLOYS BCC Alloys: Ti-V-Mn, Ti-V-Cr, Ti-V-Cr-Mn, and Ti-Cr-(Mo, Ru) Structure fcc & hcp bcc Site O T O T Number 1 2 3 6 Size 0.414 0.255 0.155 0.291 V VH VH 2 Ref.: E. Akiba and M. Okada, “Metallic Hydrides III: Body-Centered-Cubic Solid-Solution Alloys”, MRS BULLETIN/SEPTEMBER 2002 699-703

DENSITY OF STATES FOR HYDROGEN

DENSITY OF STATES FOR HYDROGEN Ref.: I. Bakonyi, F. Mehner, A. Rapp, A. Cziraki, E. Toth-Kadar, V. Skumryev, R. Reisser, H. Kronmüller and R. Kirchheim , Zeitschrift für Metallkunde (1993) Andreas Züttel, Switzerland, 17.07.14 2 8