first principles-based atomistic modeling in hydrogen fuel cell technologies: promises and...
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First Principles-based Atomistic Modeling First Principles-based Atomistic Modeling
in Hydrogen Fuel Cell Technologies:in Hydrogen Fuel Cell Technologies: Promises and ChallengesPromises and Challenges
Gyeong S. HwangGyeong S. Hwang
Department of Chemical EngineeringDepartment of Chemical EngineeringCenter for Nano- and Molecular Science and Center for Nano- and Molecular Science and
TechnologyTechnologyTexas Materials InstituteTexas Materials Institute
Institute of Theoretical ChemistryInstitute of Theoretical Chemistry
The University of Texas at AustinThe University of Texas at Austin
GREEN POWER: Hydrogen Fuel Cells
HYDROGEN + FUEL CELLS
… combines hydrogen and oxygen to produce electricity, heat, and water.
… address the two most important energy challenges: reducing carbon dioxide emissions; lowering dependence on non-renewable fossil fuels.
HydrogenFuel Cells
Fukuoka Hydrogen Town
ConnecticutAngstrom
Eco-Sailboat
Boeing
Toshiba
Rosy Outlook: Electric and hybrid vehicles, Potable electronic devices, Base load power plants, Emergency power systems, ……
"Tonight I am proposing $1.2 billion (for 5 years) in research funding so that America can lead the world in developing clean, hydrogen-powered automobiles."
The initiative’s goal is to develop the technologies
by 2015 that will enable U.S. industry to make
hydrogen-powered cars available to consumers by
2020.
January 28, 2003State of the Union Address
HYDROGEN FUEL INITIATIVE – yr 2003
Korea: The government only started funding hydrogen-related R&D in 1998, but is emerging as a major player. A new program was launched in 2004 with a budget of $586 million through to 2011.
Technical Challenges: … that needs to be addressed through R&D to pave the way for commercialization of fuel cell and hydrogen infrastructure technologies
Fuel Cell Cost and Durability
Hydrogen Production and Delivery
Hydrogen Storage
Recent Progress in R & D: Hydrogen program led by the Department of Energy (DOE) has made important progress in R & D:
reduce the cost of producing hydrogen from natural gas; develop a sophisticated model to identify and optimize major elements of a projected hydrogen delivery infrastructure; increase by 50% the storage capacity of hydrogen; reduce the cost and improve the durability of fuel cells.
MORE DIFFICULT CHALLEGES lie ahead:
• find a technology that can store enough hydrogen on board a vehicle to achieve a 300-mile driving range;• reduce the cost of delivering hydrogen to consumers;• further reduce the cost and improve the durability of fuel cells.
Fuel Cells: Fundamental Issues
ReliableReliable; Low-costLow-cost; High-performanceHigh-performance
Catalyst Research
Increasing catalytic activity, particularly for the oxygen reduction reaction (ORR) Reducing CO poisoning Developing cheaper, more abundant alternatives to Pt.
H2 2H+ + 2e–
2H+ + 2e– + ½O2 H2O
Platinum (Pt) catalysts
High Temperature (> 100oC) Membranes Water Management Stack Cooling High System Complexity Uneven Reactant Distribution ….
O2 from Air
Heat (85 oC)
H2O(g), Air
Fuel H2
Used Fuel Recirculates
Flow Field Plate
Anode Cathode
Proton Exchange Membrane (PEM)
Catalyst
ELECTRIC CIRCUIT(40%-60% Efficiency)
FC stack
Catalyst Design: Magic or Science ..??!
“Chemist Wins Nobel For Catalyst Studies”
Alchemy
Gerhard ErtlMax Planck Society
2007 Nobel PrizeIn Chemistry
Our current research is focused on gold-based bimetallic alloys, such as gold-palladium group metals.
Non-Platinum Catalysts for PEM Fuel Cells
Develop low-Pt or Pt-free metal catalysts, with similar (or better) activity and performance durability to the currently used Pt-based catalysts …
Pt monolayer supported on less expensive metals
Pt-M alloys (M=Ni,Co, Fe, Ti, V,…)
Core-Shell Nanoparticles
Novel Pt-free CatalystsBinary/ternary combinations of Pd, Au, Ag, Co … …
Why Gold-based Nanocatalysts ?
Gold nanoparticles exhibit extraordinarily high activity for various catalytic oxidation processes at or below room temperature, while its bulk counter part has
long been known to be chemically inert.
Kyle Hwang
Advantages of gold-based alloy nanocatalysts include: much less sensitive to CO poisoning than Pt less expensive than Pt bifunctional catalytic activity ---- can be used for both anode and cathode reactions in fuel cells
Metal Alloy Nanoparticles for Catalysis
50 nmfrom G.G. Scherer
PtCo/C
Anode Cathode
e-e-
H2O
O2
H2
H+
electrolyte membrane
diffusion layer
catalyst
metal-metal interaction
bimetallic nanoparticles(Pd-Au, Pt-Au, ..)
low metal coordination metal-support interaction
supported single metal nanoparticles(Pd, Pt, Au, ..)
single crystal surfaces
Metal nanoparticles are ideal catalysts, exhibiting high activity and
moreover their catalytic function can be controlled by tailoring their size and shape.
Such tunability may allow design and synthesis of next generation catalysts with:
1. Higher activity Less catalytic usage2. Higher selectivity Little or no byproducts and waste3. Longer lifetime Reduced catalyst cost
Nanocatalysts: Fundamental Issues
Catalytic properties are governed by
– particle size and shape
– particle surface composition and structure
– particle-support interfacial interactions
Weak particle-support Interactions
– shape change
– sintering
– loss of their unique properties
Therefore it is necessary to better understand:
– synthesis, structure and thermal stability of supported metal nanoparticles
– surface structure and chemistry of support materials
– dependence on catalytic activity on particle structure, metal-metal interactions in metal particles, and metal-support interfacial interactions
from Krumeich, ETH
from Goodman, TAMU
“ Better understanding the fundamentals is key to developing more effective nanocatalysts”
Rational Design and Development of Novel Bimetallic Electrocatalysts for Fuel Cell Applications through First Principles-based Atomistic Modeling
Develop a quantitative understanding of the nature and reactivity of Au-based bimetallic nanocatalysts, with particular focus on the
effects of catalyst support materials and process conditions on:
Rational Design and Synthesis
AuPd/C
Nucleation, Growth and Structure
Surface Composition and Configuration
Catalytic Activity and Poisoning
Gold-Palladium Nanocatalysts
Bimetallic palladium-gold (Pd-Au) alloys have been found to significantly increase catalytic efficiency, compared to the monometallic Pd and Au counterparts, in various reactions including:
Pd-Au catalysts have also recently received much attention for hydrogen fuel cell applications, because they are much less sensitive to CO poisoning than pure Pt or even Pt-Ru.
H2 O2
OH+OH
H2O2
O+OH
H2 O2
OH+OH
H2O2
O+OH
Direct synthesis of H2O2 from H2 and O2
Oxidation of carbon monoxide
Production of vinyl acetate monomers
…..
What alloying effects ….. ???
Direct H2O2 Synthesis: Role of Pd Ensembles
Pd-Au Pt-Au
0.24
in eV
Pd monomer
Pure Pd
0.53
1.55
0.89
0.51
Pd monomers surrounded by less active Au atoms that suppress O-O bond scission are primarily responsible for the significantly enhanced selectivity towards H2O2 formation on PdAu alloys.
Ham, Hwang et al., J. Phys. Chem. C, in press (2009)
Gold Nanoparticles on TiO2(110)
… shows strong size-dependent catalytic activity.
TiO2 supported Au nanoparticles
single crystalline Au surfaces
Tsurf < 300 K
C=O
O=O
O=O
C=O
O=C=O
… unusual catalytic activity for CO oxidation even below room temperature … Haruta, catalytic today (1997)
low metal coordination particle-support interaction ... ???
Mean particle diameter, nm
Act
ivit
y
CO oxidation
Goodman et al.Science (1998)
Gold Nanoparticles on TiO2: Surface Chemistry
Gold particle – low coordination
Au-TiO2 interface
o
A1.48
O2 adsorption & diffusion Au particle growth & structure
CO oxidation
0.4 eV
1.4 eV
Supported Au Clusters( Role of the cluster-support interface)
O2 dissociation …
CO oxidation
Supported Au Clusters ( Role of the cluster-support interface)
2.0 eV
… no sizable barrier, in good agreement with
experimental observations*
*Haruta, Gold Bul. 37, 27 (2004)
+ CO(ad)
Haruta (2004)
Promise of Atomistic Modeling
First principles-based atomistic modeling can complement experimental observations and also provide many valuable hints on how to control the structure and function of supported metal nanocatalysts, while current experimental techniques are often limited to providing complementary real space information.
This further offers an invaluable guide to the rational design and synthesis of bimetallic nanoparticle-based materials for various catalytic applications
Science 227, 917 (1985)
Computational Nanoengineering LabComputational Nanoengineering LabUT – Austin (since Fall 2001)
Synthesis Structure PropertiesSynthesis Structure Properties ……. ???. ???
TiO2(110)
Au
Metal nanocatalystsMetal nanocatalysts Semiconductor processingSemiconductor processing
Nanocrystal memoryNanocrystal memory
SiO2
Si
Supercapacitor energy storageSupercapacitor energy storage Si/Ge nanowire: batteries, thermoelectricsSi/Ge nanowire: batteries, thermoelectrics
SiAu
Si
SiO2
…. allows us to explore complex chemical and physical phenomena occurring at nanomaterials and nanosystems at the atomic scale. So it has emerged as an increasingly important area of research in nanoscale science and engineering.
Progress from the computation approach contributes greatly to realizing experimental control of materials properties in the nanoscale regime.
First Principles-based Atomistic Modeling
In past 35+ years, computational power (driven by Moore’s Law) has increased
by over 6+ orders of magnitude.
Computational modeling now ‘auto-catalyses’ its own progress exponentially!!!
Supercomputer
ENIAC (1947-1955)
Exponential Growth in Computation
AcknowledgementsCurrent & Former Group Members: Current & Former Group Members:
Fourteen (14) PhD Students Fourteen (14) PhD Students Three (3) Post Doctoral AssociatesThree (3) Post Doctoral Associates Four (4) Visiting Professors Four (4) Visiting Professors
National Science Foundation (NIRT, CAREER, SGER, CBET)National Science Foundation (NIRT, CAREER, SGER, CBET) Department of Energy (SISGR)Department of Energy (SISGR) Robert A. Welch Foundation (2002-present)Robert A. Welch Foundation (2002-present) Semiconductor Research Corporation (CSR, BEP, FE) Semiconductor Research Corporation (CSR, BEP, FE) International SEMATECH (AMRC)International SEMATECH (AMRC) Korea Institute of Science and TechnologyKorea Institute of Science and Technology Tokyo Electron, Inc. Tokyo Electron, Inc. Applied Materials, Inc. Applied Materials, Inc. SKC, KCC, Intel, University of Texas at AustinSKC, KCC, Intel, University of Texas at Austin Texas Advanced Computing CenterTexas Advanced Computing Center
Sponsors (Current & Past):Sponsors (Current & Past):