Presentation to TechConnect World 2010. High-throughput approaches for fuel cell development

1. Materials discovery with ab initio
high throughput calculations
G. Fitzgerald, G. Goldbeck
Goldbeck-Wood, J.L. Gavartin,
A. Perlov, Accelrys Software Inc
M. Sarwar, S. French, S. Garçia, A. Martinez
Martinez-Bonastre,
D. Thompsett, Johnson Matthey
TechConnect WORLD Conference, June 2010, Anaheim, CA

2. Statement
• Materials discovery typically involves exploration of very large phase space.
Bulk and surface defects Alloying Clustering
Defect decoration Surface segregation Skin formation
• Quantum and atomistic simulation technology are
sufficiently mature to be used to screen materials and
come up with lead candidates.
• Robust, yet flexible software infrastructures make it feasible to
– Screen materials even with compute-heavy simulation methods.
heavy
– Provide a knowledge and decision base for research teams. Pipeline Pilot
Web Port
Materials Studio Pipeline Pilot Client
Materials Studio Collection
© 2009 Accelrys, Inc. 2

3. Fuel Cell Catalyst application
• Market problem: Fuel Cells issues include
– High Cost
– Limited stability
• Technology problems
– Catalytic breakdown of O2 is rate determining
– Catalysis relies on Platinum
– other metals do not to perform well enough.
• R&D problems: Finding alternatives to Pt
– Different alloy combinations
– Different alloy microstructures
– i.e. Screening thousands of materials
• Modeling problem: High throughput & relevance
– Complex enumeration of periodic structures
– Long calculation times
– Property analysis relevant to experiment
© 2009 Accelrys, Inc. 3

4. PEM Fuel Cells
Overall:½O2+H2 H2O+ electricity
Anode- hydrogen oxidation: Cathode- oxygen reduction:
H2 2H+ + 2e- ½O2 +2H+ + 2e- H2 O
© 2009 Accelrys, Inc. 4

5. Voltage losses in a PEMFC
Theoretical cell voltage: 1.23V
Actual much less due to various loss processes
1.4
Theoretical Cell Voltage [E° = 1.23 V]
1.2
1
C ell Poten tial [V]
Cathode Activation
0.8 Cell Resistance
0.6 Anode Activation
Mass Transport
0.4
Cell Performance
0.2
0
0 200 400 600 800 1000 1200 1400
Current Density [mA/cm2]
© 2009 Accelrys, Inc. 5

6. Dissociative ORR mechanism in PEMFC
Adsorption of O2 Dissociation of O2 Combination with a proton
+e-….
e-
….to form OH ….to form H2O
e-
Combination with a
second proton +e- ….
© 2009 Accelrys, Inc. 6

7. Ideal Catalyst – Sabatier’s Principle
• The optimum catalyst-adsorbate interaction must
adsorbate
– Not be too weak:
• Chemical bonds between surface and adsorbate can be formed
• Internal bonds weakened so intermediates can be generated
– Not be too strong
• Intermediates generated can react further
• Desorbtion takes place and freeing up of adsorption sites
• Pt is close to optimum, but expensive
– Other pure metals perform worse
– What about alloys?
Pt
Catalytic
Activity
Metal-adsorbate bond strength
© 2009 Accelrys, Inc. 7

8. Phase Space
Activity
0% - Pt 50% - Pt 100% - Pt
100% - Co 50% - Co 0% - Co
With high throughput modeling, phase space to be explored
that would otherwise not be covered experimentally.
© 2009 Accelrys, Inc. 8

9. Sampling must include structure and composition
Bulk and surface defects Alloying Clustering
Defect decoration Surface segregation Skin formation
…
© 2009 Accelrys, Inc. 9

10. Overview of approach
• Objective: find alloy with similar profile as Pt, slightly weaker bonding
Pt
Catalytic
Activity
• Generate representative catalyst surface models
Metal-adsorbate bond
strength
• Calculate key properties and determine descriptors of ORR
activity and bonding:
– Material Stability (Segregation Energies)
– O adsorption Energies
– OH adsorption Energies
– d-band centres
– electronic workfunction
Work function
– thermodynamics of reaction steps
• Methodology:
– Plane Wave Density Functional Theory – CASTEP
– High throughput strategies, automation
– Data accumulation and storage in database
– Data Management and reporting
© 2009 Accelrys, Inc. 10

11. High throughput calculations: Overview
© 2009 Accelrys, Inc. 11

12. AxB1-x ensemble generation
For a given supercell generate all
1st layer `A` configurations with k out of N host
2nd layer `B` sites substituted by X atoms
A0B2C2D0
3rd layer `C`
4th layer `D` N N!
 =
 k  k!( N − k )!
Constrained atoms
Define a configuration class by the
number of substitutions in each layer
A A A A B B B B C C C C D D D D
Map each structure into a unique
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
binary string
0 0 0 0 1 1 0 0 0 0 1 1 0 0 0 0
Apply symmetry transformations
and find degeneracy of irreducible
configurations
© 2009 Accelrys, Inc. 12

13. Example Pt3Co: 6 layers slab setup
N=16, k=4
16!
= 1820 configurations
4!(16 − 4)!
133 – non-equivalent configurations (due to symmetry)
equivalent
Pt not stable on surface of Pt3Co -> only consider A0 superclass
A0 superclass contains 42 irreducible configurations
A0 superclass structures
Class Conf. x gi Class Conf. x gi Class Conf. x gi Class Conf. x gi Class Conf. x gi
A0B4C0D0 1x1 A0B3C1D0 1x12+1x4 A0B2C2D0 2x6+1x24 A0B1C3D0 1x4+1x12 A0B0C4D0 1x1
A0B3C0D1 1x12+1x4 A0B2C1D1 4x12+2x24 A0B1C2D1 4x12+2x24 A0B0C3D1 1x12+1x4
A0B2C0D2 2x6+1x24 A0B1C1D2 4x12+2x24 A0B0C2D2 2x6+1x24
A0B1C0D3 1x12+1x4 A0B0C1D3 1x12+1x4
A0B0C0D4 1x1
© 2009 Accelrys, Inc. 13

14. Pt3Co: most stable configurations
a b c d
E = E0 E = E0 + 0.03 eV E = E0+ 0.04 eV E = E0+0.07 eV
∑ g je
− ( E j − E0 ) / k BT
Z4 = = 0.96
j =1, 4
∑g e
− ( E j − E0 ) / k BT
Z11 = j = 0.999
j =1,11
~11 configurations give significant contribution into the TD average.
Entropic factor may be important J. L. Gavartin et al., Transactions of the
Electrochemical Society 25(1) 1335-1344 (2009).
© 2009 Accelrys, Inc. 14

15. Surface phase diagram
• stoichiometry near the surface may significantly deviate from its nominal bulk value.
Understanding surface phase diagram is critical for
– assessing catalytic reactivity
– testing electrochemical stability
thermodynamic fraction fk of metal X in the layer k
Pd3Co: The thermodynamic Co fraction in the
second and third layers is overstoichiometric;
Pt3Co : The variation of Co fraction between the
layers is somewhat less pronounced.
Shuo Chen et al Am. Chem. Soc./ 2008, 130, 13818
© 2009 Accelrys, Inc. 15

16. Effect of lattice strain on oxygen adsorption
1
Ead = E (O* + surface) − E ( surface) − E (O2 )
2
Compressive lateral strain leads to
approximately linear decrease of the
Oxygen adsorption energy, while lattice
expansion leads to an increase of Eads(O).
A similar trend was reported earlier for
Cu(111), Ru(0001) and Au(111) surfaces.
Y. Xu, Surf. Sci., 494, 131-144 (2001).
M. Mavrikakis, Phys. Rev. Lett., 81, 2819 (1998).
M. Mavrikakis, Catal. Lett., 64, 101 (2000).
O adsorption on most stable (Pt/Pd)3Co
surfaces suggests some additional efects
besides strain, e.g. chemical modification
and surface relaxation.
© 2009 Accelrys, Inc. 16

17. High throughput materials calculations
© 2009 Accelrys, Inc. 17

18. Creating the discovery database
© 2009 Accelrys, Inc. 18

19. Reporting and mining the database
© 2009 Accelrys, Inc. 19

20. Calculations database: Portal
Access via a Web Portal:
1. Choose the database name (local or remote)
2. Choose composition of a material of interest
3. Choose report tables to show
© 2009 Accelrys, Inc. 20

21. Calculations database: systems overview
Statistics for all selected jobs: Run time and CPUs used
Systems categorized as bulk, slab or molecule and shown by chemical composition
Choose the chemical composition of interest
© 2009 Accelrys, Inc. 21

22. Calculations database: Table of runs for a system
Sortable tables display key job information (a single calculation per line):
Choose the specific individual calculation to see all its details
© 2009 Accelrys, Inc. 22

23. Calculations database: Job details
The details are given in different tables, that may be shown or hidden
Jmol visualiser for structure viewing, manipulation and analysis
© 2009 Accelrys, Inc. 23

24. Results details: Workfunction and d-band centre
band
© 2009 Accelrys, Inc. 24

25. Oxygen Reduction Reaction
E
E0=E(O2+*)
ETS=E(O*-O*)
E1=E(O2*)
E2=2E(O*)
Reaction coordinate
Ediss=E2-E1 Eads1=E1-E0
Ea=ETS-E1 Eads2=E2-E0
Eads1=E1-E0
© 2009 Accelrys, Inc. iCatDesign
25

26. Reaction free energy protocol
•Calculate free energy of main steps of dissociative ORR reaction as
Calculate
a function of cell potential U
On input:
File with energies
Cell Potential U
Substrate
O adsorbed
OH adsorbed
H2O and H2 gas phase
Correction energies
(-ST, ZPE, solvation)
1. J.K. Nørskov, J. Rossmeisel, A. Logadottir, et al.J. Phys. Chem. B,108, 17866
17866-17892 (2004).
© 2009 Accelrys, Inc. 26

27. Reaction free energy protocol
© 2009 Accelrys, Inc. 27

28. Summary
• A series of tools and models have been developed for screening various Pt alloy
combinations for stability and activity.
• Tools developed can be used to screen Pt and non
non-Pt compositions
• ORR activity is improved by lattice strain (compressive for Pt)
• Strain is controlled by alloying with base metals antisegregating away from the
surface (typically metals with smaller atomic radius)
• D-band centre, surface segragation and adsorption energies are found to be useful
band
descriptors
© 2009 Accelrys, Inc. 28

29. Conclusions: High Throughput Calculations
• Materials Discovery beyond the trivial case requires a vast number of
systems to be studied, each requiring HPC computing itself.
• Successful projects require collaboration of different organizations and
modeling with experiment.
• Require new strategies allowing for large multi
multi-platform and multi-user
collaborative projects providing automation in
– optimization of calculations
– strict quality control
– streamlined analysis and reporting
– Data storage and mining in a flexible, extensible database
• Pipeline Pilot and the Materials Studio Collection have been used to
– Build a framework for Materials HTC
• Automated job generation, execution and analysis
• Datamining via web portal
– Screen >2000 catalyst leads and identify candidates for development
– Provide a source for project teams to explore.
© 2009 Accelrys, Inc. 29

30. Acknowledgements
• Dan Ormsby J. L. Gavartin, M. Sarwar, D. C. Papageorgopoulos, D. Gunn, S. Garcia,
A. Perlov, A. Krzystala, D. L. Ormsby, F. Liu, G. Goldbeck
Goldbeck-Wood, A.
• Amity Andersen Andersen, S. French, D. Thompsett. Exploring fuell cell cathode
materials: High throughput calculation approach.
• David Gunn Transactions of the Electrochemical Society 25(1) 1335-1344 (2009).
• Arek Krzystala
• Victor Milman
• Patricia Gestoso-Suoto
Funding:
This project is partly funded under Technology Strategy Board Project Number:
/5/MAT/6/I/H0379C. The TSB is a business
business-led executive non-departmental public body,
established by the government. Its mission is to promote and support research into, and
development and exploitation of technology and innovation for the benefit of UK
business, in order to increase economic growth and improve the quality of life. It is
sponsored by the Department for Innovation, Universities and Skills (DIUS) (22).
© 2009 Accelrys, Inc. 30