1

Energy Research for SustainabilityMatthew M F Yuen, Ph.D. (袁 銘 輝 )

Acting Vice President for Research and Development

ASPIRE FORUMTOKYO INSTITUTE OF TECHNOLOGY, 5TH JULY,

20101香港科技大學

THE HONG KONG UNIVERSITY OF SCIENCE AND TECHNOLOGY

2

Energy/Capita Consumption 2009

Source: BP Statistical Review of World Energy Consumption June 2010

3

World Primary Energy Consumption 2009Source: BP Statistical Review of World Energy Consumption June 2010

4

World Energy Projection 2030Source: EIA International Energy Outlook 2010

5

Energy/GDP Projection 2030

Energy demand 35% higher in 2030

Energy efficiency

improves by 65%

Source: ExxonMobil - Outlook for Energy – A view to 2030

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Industrial Energy Demand

Industrial energy demand dominant: Green manufacturing

Source: ExxonMobil - Outlook for Energy – A view to 2030

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Green Manufacturing

• Manufacturing with reduced waste and pollution through innovative product and process design, including the use of new materials and supply chain.

• “Cradle to Cradle” process - reuse/recycle• Minimum damage to environment and human,

low energy consumption

Sustainability

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Green PLM - Opportunities

• Design for sustainability• New materials – recycle / reuse• Novel green processes • Efficient supply chain

New regulations – ISO 50001What is required? – INNOVATION

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Green Product Lifecycle ManagementSource: Environmental Logic

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Green PLM - Apple

• Manufacturing– Material use– Toxic substance removal– Responsible manufacturing

• Transportation– Smaller packaging

• Product use– Energy efficiency

• Recycling– Product recyclability– Apple recycling program– Responsible recycling

• Facilities– Facilities in the big picture– Energy use– Employee commuter program

Source: Apple

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Renewable Energy Investment 2008Source: Renewables Global Status Report 2009 Update

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HKUST Cases in Energy ResearchEnergy Research & Material Research

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The energy problems are…...

• People really like using electricity, and their vehicles!

• Fossil fuels are being depleted• Global warming (CO2

production )• Air pollution caused by thermal

power generation and IC engine exhaust

Fossil fuel systems are not sustainable

Turbine or IC engine

O2 Fuel

Heat

CO2

Combustion

NOx, SOxParticulates

Mechanical energy

Electric generator

Electricity

Vehicles

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Sustainable Energy Future

Two conditions must be satisfied:

Need to re-organize the entire energy system for a sustainable energy future

2. Energy must be distributed and converted with highest efficiency

1. Energy source, sink, handling and use must besustainable

Ulf Bossel – October 2005

15Sustainable Energy Future

C-free Sources:

Consumers need motion, sound, light, heat, communicationUtilization:

Renewable or nuclear power plants

H2O + CO2

H2O + CO2

e- H2

H2O

Electrolysis

H2 Fuel Cell

e-

Biomass

Methanol or Ethanol

Methanol or EthanolFuel Cell

e-

H2O

Battery

e-

C-free cycle C-neutral cycle

Hydropower, Ocean energy, Geothermal

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Case I: Direct Alcohol Fuel Cell

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Simple molecule– Less demanding on catalyst.

Liquid at room temperature and ambient pressure.- High energy density; readily available fuel

infrastructure. Made from natural gas or

renewable resources – Low cost, sustainable.

Why alcohol?

OC

H

H

H

HC

H

H

OC

H

H

H

H

Methanol

Ethanol

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How does DAFC work?

Alcohol solution

Direct Alcohol Fuel Cell

Methanol, Ethanol

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Single cell structure

Carbon

Flow field plate

Flow field plate+-

Anode flow channel Cathode flow channel CO2 bubble

Water

H+

Alcohol

Water/AlcoholOxygen or air with water

e-

e- e-

e-

Anode diffusion layer

Anode catalyst layer

Polymer Electrolyte

Diffusion layer

Cathode diffusion layer

Cathode catalyst layer

Catalyst particle on carbon support

Load

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Why DAFC?

The DAFC system: Simple system design (no

reformer, no humidifier) Promise of high efficiency Silent operation (no noise) Operable at room temperature

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Applications of DAFC

Ideal for mobile applications such as laptops, cellular phones

Also of great interest to the military – to power individual soldiers’ electronics

Next generation of road vehicles Distributed power generation.

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Technical Challenges for DAFCE

lect

rode

pot

entia

l / V

olta

ge

Anode electrode

Cathode electrodeKinetic loss(200-300 mV)

Electrode resistance

Oxygen transport(>100 mV)

Electrolyte resistance

Electrode resistance

Kinetic loss(200-400 mV)

Current density

1.2

Alcohol crossover(25-150 mV)

Catalyst development

Catalyst development

Electrode material development

Electrode material development

Membrane modification and development

OCV loss due toalcohol crossover

Rapid drop-off due to

activation losses

Linear drop-off due to ohmic losses

Mass transport lossesAlcohol transport(25-150 mV)

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Nano-catalysts Development

PtRu nano-particles (3-4 nm) on nanotubes

Pt nano-particles (2-3 nm) on nanotubes

Prabhuram, Zhao, Yang, J. Electroanalytical Chemistry, 578 (2005) 105-112.Prabhuram, Zhao, Tang, Chen, Liang, J. Physical Chemistry B, 110(2006) 5245-5252.Prabhuram, Zhao, Liang, Chen, Electrochimica Acta, 52 (2007) 2649-2656.

20 nm

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Anode Backing LayerXu, Zhao, Ye, Electrochimica Acta, 51 (2006) 5524-5531.

PEM

Cathode DL

Cathode CLAnode CL

Anode DL

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Mathematical Modeling

Fuel

Oxide

Liquid Gas

Liquid Gas

Anode region

Cathode region

Yang, Zhao, J. Electrochemical Society 52 (2007) 6125–6140

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( ) ( ){[ ] [ ]) (}( )c

lc l

eff effrg rgco co

g

cc

g

lo

dp s pKk s Kk sD D N

RTp p p p

RT RTd RTsµ µ∇ − − +∇ − − =∇

+ +∇∇

2

2 2

.( ) ( ) 0

/ /rl rl

lll l l l

lKk Kk g m Consumptionp ρµ ρ µ ρ

∇ ∇ =∇ − +

APR

( ) ( ) ) ~effml m m l l l m M m

l

cU c D c U U c D c N MORρρ

∇ −∇ ∇ = ∇ + ∇ − ∇ = ∇2m(

2M H Oeff m effM mem M d mem M d

Water

C MI IN D C n D C nF Fρ

= − ∇ + = − ∇ +Mem

( )w Mem lW d

l Water

I k dpN nF dy M

ρµ

= −

AFC

.interface[ (1 ) ] l

ll g lac

mu mh

ρ α∇ − = − = −

[ (1 ) ] [ ] sin 2 | |ml g l l g g g g M mixture mixture

h

fu u u u p g u uD

ρ α ρ α ρ θ∇ − +∇ = −∇ − −

0[ (1 ) ] | |g g g g l gju C u u Uα α= + − +

.ginterface[ ] gg g g

ac

mu m

hρ α∇ = =

.

interface[(1 ) ] mmg l M

ac

Nu c Nh

α∇ − = − = −

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. interface

.ginterface

[ ]

[ (1 ) ]

l

evporationl ll l l

cc cc

vapor c o evporationgg l g

cc cc

m m mu mh h

m m m m mu mh h

ρ α

ρ α

−∇ = = =

+ − +∇ − = = =

l g mu u u= =

. interface

. interface

[(1 ) ]

[(1 ) ]

ool o

cc

evaporationvvl v

cc

Nuc N

hN N

uc Nh

α

α

∇ − = − = −

+∇ − = =

CFC

~effV V V VN C D C Evaporation rate= − ∇gU

CPR( ) ( )

[( ( ))( ) ( ( )) ]

CL

L c Lrl rl L

L L

D s

g

f s

K dp Kk s k s ms

pd

sρ ρµ µ

∇ − + −∇ =∇−

( ) {[ ( )] }gas rg gasg s

ga

K k s p mρν

∇∇ = −∇ =gU

~effO O O ON C D C ORR= − ∇

2 2 2 2gU

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Power Density - DMFC

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State-of-the-art performance of acid DEFC

J. Power Sources 140 (2005) 50-58

Anode: PtSn, 1.3 mg cm-2

Cathode: Pt, 1.0 mg cm-2

Membrane: Nafion 115

Maximum power density: 28 mW/cm2

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Alkaline DEFC

Loade- e-

OH-

OH-

OH-

EtOH

CO2

Air

Exhaust gas

Anode CathodeAEM

Pt-free catalyst Better electrode kinetics Lower fuel crossover Low cost alkaline membrane Less material corrosion

o2 5 2 2 2C H OH 3O 2CO 3H O 1.145VE+ → + =

- - o2 5 2 2C H OH 12OH 2CO 9H O 12e -0.743VaE+ → + + =

- o2 23O 6H O 12e 12OH 0.401VcE−+ + → =

AnodeCathodeOverall

Ethanol:

Y.S. Li, T.S. Zhao, Z.X. Liang, J. Power Sources 187 (2009) 387–392.

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Anion Exchange Membrane

(a) surface (b) cross section (Low resolution)

(c) cross section (High resolution)

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Catalysts

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Alkaline DEFC: State-of-the-art performance

0 100 200 300 400 500 600 7000.0

0.2

0.4

0.6

0.8

1.0

0

20

40

60

80

100

120

Powe

r den

sity,

(mW

cm

-2)

Temperature: 60 oC

Cell v

olta

ge, (

V)

Current density, (mA cm-2)

Current AEM-DEFC Typical PEM-DEFC

Maximum power density: 110 mW/cm2 (Acid type: 15 mW/cm2)

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DEFC

Ethanol + Water

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Mobile Phone Battery Charger

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MP4 Player

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Case II: High Power LED

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HP-LED for solid state lighting• Advantages:

– long operating life (>50,000 hours), – high efficiency, – high reliability, – environmental friendly, – vivid color – compact size

• LEDs form a rapidly growing segment of the global lighting market, estimated at $75 billion a year in 2008.

lower operating costs

[Multi-Year Program Plan (FY’09-FY’15) of SSL R&D, US Department of Energy, Mar. 2009]

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Thermal Challenge in HP-LED Packages• Higher power density results in increasing

thermal challenge.• Effect of junction temperature increase

– Luminance of HB-LEDs will reduce linearly – Life will reduce exponentially– Color will shift with temperature

(N. Narendran and Y. Gu, 2005)

70 mW, 2 lm

>10 W, >100 lm

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Heat Conduction Plays an Important Role• LEDs: generated heat is dissipated mainly by conduction at the

source, while for conventional light sources radiation is dominant.• Thermal interfaces in the conduction path are pivotal for LED

performance

Power LED

light: ~15..40%

heat loss: ~85-60%, mostly by conduction

100 W incad. lamp

light: 5%dissipated heat: 12%

IR radiation: 83%

-

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Heat Dissipation Bottleneck: TIM and Heatsink• TIM: thermal interface material

– To reduce the thermal resistance at the interface between the heat source and the heat sink

• Improve heat convection of heat sink

Primary heat dissipation path

TIM

Au wire

InterposerHB-LED device

Heatsink

Heat slug

Heat sink

DeviceTIMAir RTIM-heatsink

RTIM

Rheat source-TIM

Air gap exists at the interface

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Improve the Thermal Conductive Performance• Thermal resistance can be reduced with proper choice of TIM.• Conventional TIM cannot meet the thermal dissipation requirement• VACNT-TIM is promising

Heat sink

DeviceAir

Heat sink

DeviceCNT-TIM

Air

Heat sink

DeviceSilver epoxy Air

R = 107 mm2K/W R = 75 mm2K/W

R = ? mm2K/W

RTIM-heatsink

RTIM

Rheat source-TIM

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VACNT-TIM Synthesis by Thermal CVD

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Thermal Performance of CNT-TIM on Si Substrates• Commercial silver epoxy: 75 mm2·K/W• CNT-TIM grown with thermal CVD on Si substrates: 15 mm2·K/W• CNT-TIM grown with PECVD on Si substrates: 7 mm2·K/W

(Kai Zhang, et al, Nanotechnology, Vol.19, pp.215706, 2008)

10 nm

Heat sink

Device

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MD Model of CNT

• Cell dimensions: 16.6Å x 16.7Å x 24.5 Å• All atoms are unconstrained.• Boundary conditions: periodic in x and y directions• Iteration time interval – 1femtosecond (fs)• Temperature: 25oC

24.5nm XY

Z

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NEMD Simulation-Given Constant Heat Flux

AEABBR k 2/])4([1 2/12 ∆++−+=Hot region:

24.5nm XY

Z

Hot region +Cold region - kE∆ kE∆

Based on the NEMD algorithm (Ikeshoji and hafskjold, 1994)

AEABBR k 2/])4([1 2/12 ∆−+−+=Cold region:

subii vvRv −=′Velocity rescaling:

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NEMD Simulation

The heat flux was given as follows:tS

EJ∆∆

=

where is the heat flux of the CNT, is the cross-section area of the CNT, is the simulation time step

J S t∆

The instantaneous local temperature in each region is given as follows:

∑=

=kn

iii

Bkk vm

knT

1

2

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Where is the amount of atoms in region , is Boltzmann’s constant, andrespectively, are the mass and velocity of atoms

kn k Bk im iv

i

>∂∂<><

=ZT

J/

λ

The thermal conductivity of the CNT, , can be calculated by the Fourier law:λ

48

Temperature Profile Along the SWCNT under Tension stress (50MPa)

y = 0.8606x + 287.7

0

50

100

150

200

250

300

350

400

0 5 10 15 20 25Z (nm)

Tem

pera

ture

(K)

Temperature distributed linearly along the CNT with a temperature gradient

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Thermal Conductivity of SWCNT under Different Conditions

• Thermal conductivity of CNT was dependent on the applied stresses.

• The thermal conductivity monotonically decreased with the stress changing from the compression to tension.

• The thermal conductivity of the CNT subjected to torsion stress decreased with the increase of torsion stress.

• The thermal conductivity of CNT was degraded by the moisture inside the tube.

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CNT-TIM on Al Alloy Substrates• Problem of CNT-TIM on Si Substrates

– Conflict between CNT synthesis and device fabrication if CNTs are grown on backside of Si devices

• Potential Solutions 1. CNT-TIM synthesized on Si substrates and then transferred to Al alloy

heatsink: not viable2. CNT-TIM synthesized on metal foil and then sandwiched in between device

and heatsink: easy to handle3. CNT-TIM synthesized directly on Al alloy heatsink customized production

Solution 2 Solution 3

Device

Solution 1

DeviceDevice

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Thermal Resistance Measurement

• Sample packages were designed to take into account the contact conditions as well as the bulk thermal performance of TIM.

Si

Al alloy

TIM

Heaters

Cooler

Load cell

Sample

Holes for RTDs

Pressure transducer

Copper bars

(ASTM D5470)

RTIM-heatsink

RTIM

Rheat source-TIM

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Light Power Testing for LED• The output light power of a LED package is measured by PMS-50

analytical system with an integrating sphere.

Integrating Sphere PMS-50 analytical system

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Thermal Performance Improvement• The thermal resistance of CNT-TIM synthesized on Al substrates

is reduced to 4 mm2K/W.• Compared with CNT-TIM on Si substrates, CNT-TIM on Al

substrates with lower resistance is achieved by better adhesion between CNTs and substrates.

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RTIM-heatsink

RTIM

Rheat source-TIM

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HB-LED with VACNT-TIM (CVD) on Al Alloy Substrates• 10 W LED module with 3×3 LED chip array• HB-LED with commercial TIM burnt out at input power of 3000 mA• HB-LED with VACNT-TIM provides the LED package with a better brightness

performance and survives at the input current as high as 3750 mA.

(Kai Zhang, et al, 58th ECTC, pp.1659-1663, 2008)

0

300

600

900

1200

1500

1800

0 1000 2000 3000 4000Input current (mA)

Out

put l

ight

pow

er (m

W)

Commercial TIMVACNT-TIM on heatsinkIdeal thermal management

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HB-LED with VACNT-TIM (PECVD) on Si Substrates• VACNT-TIM > Commercial TIM• CNT quality influences the brightness

performance of HB-LED

(Kai Zhang, et al, Nanotechnology, Vol.19, pp.215706, 2008)

020406080

100120140160

0 200 400 600 800 1000Input current (mA)

Out

put l

ight

pow

er (m

W)

Commercial TIMCNT1CNT2CNT3Ideal thermal management

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56

Application in HB-LED packages

1×1 mm2 LED chip

LED assembly

LED package

3×3 LED module

CNT-TIMThermal conductive polymer

Heatsink

(Courtesy Advanced Packaging Technology Ltd.)

57

Packaging Process in Ultrahigh Power HB-LED

Thermal conductive polymer

Put LED device on the VACNT-TIM1; put some thermal conductive polymer around the device and CNTs using a dispenser and let it cured

Put the module on a heatsink; put some thermal conductive polymer around the module and VACNT-TIM2 using a disperser and then let it cured

Synthesize VACNT-TIM on both sides

Heatsink

LED device

Thermal conductive polymer

VACNT-TIM1

Heat spreader

Heat spreader (a)

(c)

(b)VACNT-TIM2

Heat spreader

(Kai Zhang, et al, CIRP Annals-Manufacturing Technology, Vol.56, pp.245-248, 2007), (Matthew M.F. Yuen, K. Zhang, US patent 11/752,955, 2007.)(Matthew M.F. Yuen, K. Zhang, Chinese patent 200710106382.6, 2007)

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Summary – LED Lighting• VACNT-TIM fabricated by PECVD on Al alloy substrates

– Well aligned, high density– 4 mm2·K/W, about 6% of that of commercial TIM.

• A novel heat spreader with double sided VACNT-TIM• Possible use in convection cooling • VACNT-TIM is promising for thermal management in high power

HB-LED application.

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Energy Institute @HKUST

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Energy Institute @ HKUST• Current Research Centers

– Center for Sustainable Energy Technology– Center for Display Research– Center for Advanced Microsystem Packaging– Finetex-HKUST R & D center– Photonics Technology Center– Building Energy Research Center – HKUST-Foshan LED-FPD Research Center

• Energy Institute anchored in School of Engineering encompassing research in: – School of Science – new materials, …– School of Business - economics, …– School of Social Science and Humanities – policy,..

Coordinated Research Program for SUSTATAINABLE Development

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Thank you!