Atomistic simulations of a promising solid oxide fuel cell cathode materials Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ Electronic Structure Phase Stability Oxygen Migration Energetics using Nudged Elastic Band (NEB) Shruba Gangopadhyay Email: shruba at gmail.com University of California, Davis IBM Research – Almaden This work performed at University of Central Florida . 1 If you are interested in my recent exciting (Li-air) battery related work please contact me directly
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Atomistic simulations of a promising solid oxide fuel cell
cathode materials Ba0.5Sr0.5Co0.8Fe0.2O3-δ
Electronic Structure
Phase Stability
Oxygen Migration Energetics using Nudged Elastic Band (NEB)
Shruba Gangopadhyay
Email: shruba at gmail.com
University of California, Davis
IBM Research – Almaden
This work performed at University of Central Florida
. 1
If you are interested in my recent
exciting (Li-air) battery related
work please contact me directly
Solid Oxide Fuel Cell -SOFC
Anode - Ceria/Nickel cermet
Electrolyte - Gadolinia doped Ceria (CGO)
Cathode - LSCF (a four component oxide based on
La, Sr, Co, and Fe oxides)
2
Preferred structure of cathode materials
Cathode materials are Oxygen rich oxides
Perovskites represented by ABO3
A= Lanthanides/Group IIA
B= Transition metals
3
Perovskites (SrCoO3)
For a good SOFC cathode
No phase transition
Ease of oxygen migration
BSCF – new perovskite for SOFC
Perovskites represented by ABO3, Ba0.5Sr0.5Co0.8Fe0.2O3-δ
A= Ba or Sr
B= Fe or Co
Constructed a model supercell 2x2x2 cell
4Shao, Z. P.; Haile, S. M., Nature 2004, 431, (7005), 170-173.
BSCF - no phase transition
5Wang, H. H.; Tablet, C.; Feldhoff, A.; Caro, H., Journal of Membrane Science 2005, 262, (1-
2), 20-26.
Dependence of lattice parameter
w.r.t temperature
Closest Analog SrCo0.8Fe0.2O3 shows vacancy ordering
Oxygen vacancies in BSCF
6
Oxygen non-stoichiometry ″δ ″
Shao, Z. P.; Haile, S. M., Nature 2004, 431, (7005), 170-173.
BSCF as a function of temperature at the
oxygen partial pressures indicated
We need to remove maximum
Four oxygen from supercell
Activation energy of oxygen migration
7
D chem = Rate of diffusion
Ea = Activation energy
D0 = Temperature independent
pre exponential factor depends
on lattice vibrations and jump
distance
k = Boltzmann constant
T = Temperature
Self diffusion coefficient measures ease of oxygen mobility
Our goals
Electronic Structure of BSCF
Validation with Lattice Parameter
Ground Spin state of Transition Metal (B)
cations
Stable Cation Arrangement
Phase stability of BSCF
Stable most vacancy position
Activation Energy of Oxygen Migration
8
DFT-simulation of BSCF
Self-Consistent field calculation
Plane wave basis set
PBE Functional
Vanderbilt Ultra-soft Pseudo potential
Marzari-Vanderbilt cold smearing
9
Structural Optimization
BFGS algorithmPopulation Analysis
Löwdin population analysis
Activation Energy for Oxygen Migration
Symmetry Constarined Search and Nuged Elastic band(NEB)
Quantum Espresso (Extensible Simulation Package for