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Electrochemical Energy Conversion and Storage

Yang Shao-HornElectrochemical Energy Laboratory

Department of Mechanical Engineering

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Fuel Cells

ElectricityGrid

Wind

PVSystems

Engines

Electrical EnergyStorage

Electrochemical Energy Systems

High energy conversion efficiencies 40%-95%

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Power Densities of Energy Systems

0.65MW/m3

excluding H2 storage

1.75MW/m3

Fuel Cell Systems(DOE 2010 target for transportation)

Proton Exchange Membrane Fuel Cell stacks (2001 GM)

2-3MW/m3Lithium Batteries

30MW/m3Electrochemical Supercapacitors

100MW/m3IC engines

Power densityEnergy conversion and storage devices

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System Power Requirements and Challenges

10-1 100 101 102 103 104 105 106 107 Load in Watts

Lithium Batteries

Fuel Cells

Cost/PerformanceDurability

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Anode Cathode

H2 O2/Air

H2O

Electrical Load

e- e-

Carbon SupportedPt Particles

H+ OH+

H2O H2O

H+ OH+

H2O H2O

Proton ExchangeMembrane

Membrane Electrode Assembly (MEA)

Operating Temperature 80°C

Nafion type membrane

Carbon SupportedPt Particles

Proton Exchange Membrane Fuel Cells

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0 0.5 1 1.5 2

0.2

0.4

0.6

0.8

1

1.2

Current density [A/cm2]

Cel

l vol

tage

[V]

Cell voltagePower density

Pow

er d

ensi

ty [W

/cm

2 ]

Voltage Loss Contributions in Fuel Cells

Activation Barrier-Aln(i/io)

Mass Transport lossesBln(1-i/il)

TemperaturePressure

Catalyst typeSurface area

E = Eo – i*R – Aln(i/io) + Bln(1- i/il)

Cell temperature : 80 °CH2/O2 pressure at 100kPaNafion 112 catalyst coated membrane : Pt 0.3 mg/cm2

Carbon cloth : E-Tek Teflon / Vulcan XC-72 carbon treated

A 5cm2 PEM fuel cell

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Fuel Cell Electrode Architecture

Triple phase boundaries (TPB)

carbon

PtH+

PEMFCs

Pt nanoparticles Carbon particles

ElectrocatalysisSurface/Interfacial

phenomena

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General Requirements for Fuel Cell Electrodes

• High TPB length per electrode surface and volume (Activation)• Electronic and Ionic conductivity (Ohmic)

• 3D nanopores for transport of gaseous molecules (Transport)• Chemical and mechanical stability

Cost DurabilityPower

Electrode - 0.2 mg/cm2 of Ptprojected $275/kW

target $30/kW

Current - 1500 hourstarget - 5000 hours for

transportation

PEM Fuel Cell Electrode DegradationNew Electrode Architecture

Diagnostic Tools and System ModelingInnovative Fuel Cell Structure and Assembly

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Research in Electrochemical Energy Systems

Electrochemical ActiveMaterials

System Designand Fabrication

Materials processing

New Materials

Materials Degradation

NewElectrode

MicroFabrication

2Dè 3D

Lithium Batteries PEMFCs SOFCs Metal-Air hybrid

System Diagnostic and Modeling

Electrolytic Cells

Electrochemical Systems

Diagnostic ToolDevelopment

Multi-scaleModeling

Cell and Stack DesignManufacturing

OpticalMeasurements

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New Energy Course - School of Engineering

Fundamentals: Chemical thermodynamics and kinetics

Processes: CombustionReformingElectrochemical energy conversion - Fuel CellsElectrochemical energy storage - BatteriesHydrogen storage

FUNDAMENTALS OF ADVANCED ENERGY CONVERSION

2.996, Spring 2003Ghoniem, Shao-Horn, Kazimi and Tester