maryland hydrogen seminarmar 11, 2011 · maryland hydrogen seminar march 11, 2011 greg jacksona...

Maryland Hydrogen SeminarMarch 11, 2011

Greg Jacksona and Peter Sunderlandb

a Dept. of Mechanical Engineeringb Dept. of Fire Protection EngineeringUniversity of Maryland, College Park, MD, USA

Sponsored by Virginia Clean Cities

Univ. of Maryland Energy Research Center College Park, MD

Acknowledgements• Thanks to the U S Dept of Energy Office of Energy Efficiency and• Thanks to the U.S. Dept. of Energy Office of Energy Efficiency and

Renewable Energy for providing support for the Virginia Clean

• Thanks to the following for providing slide material– Catherine Grégoire Padró from Los Alamos National Laboratory– Sunita Satyapal from DOE Hydrogen and Fuel Cell Program– Pat Hearn from Ballard Power Systems – John Turner from National Renewable Energy Laboratory– Santosh Limaye – now with Vesta Ceramics, LLCSantosh Limaye now with Vesta Ceramics, LLC – Robert Kee from Colorado School of Mines


Agenda for Seminar9:00 – 9:15 – Introduction from Univ. of Maryland Energy Research Center,9:00 – 9:15 – Introduction from Univ. of Maryland Energy Research Center,9:00 9:15 Introduction from Univ. of Maryland Energy Research Center,

Prof. Eric Wachsman, Director9:15 – 9:45 – Our current energy infrastructure and potential for hydrogen,

Prof. Greg Jackson

9:00 9:15 Introduction from Univ. of Maryland Energy Research Center, Prof. Eric Wachsman, Director

9:15 – 9:45 – Our current energy infrastructure and potential for hydrogen and fuel cells, Prof. Greg Jackson

9:45 – 10:05 – Review of alternate fuels, advanced technology vehicles and prospects for hydrogen, Chris Rice, Maryland Energy Administration, Prof. Jackson

9:45 – 10:05 – Review of alternate fuels, advanced technology vehicles and prospects for hydrogen, Chris Rice, Maryland Energy Administration, Prof. Jackson

10:05 – 10:15 – Break10:15 – 10:45 – Stationary applications and prospects for hydrogen and fuel

cells , Jackson


cells , Jackson10:45 – 11:15 – Hydrogen production, storage, and distribution, Jackson11:15 – 12:00 – Hydrogen safety and fire hazards, Prof. Peter Sunderland12:00 – 1:15 – Lunch and GM Fuel Cell Equinox Ride‐N‐Drive

10:45 – 11:15 – Hydrogen production, storage, and distribution, Jackson11:15 – 12:00 – Hydrogen safety and fire hazards, Prof. Peter Sunderland12:00 – 1:15 – Lunch and GM Fuel Cell Equinox Ride‐N‐Drive1:15 – 2:00 – Hydrogen infrastructure and regulations, Sunderland2:00 – 2:30 – Short- and- long-term prospects and discussion, Jackson2:30 – 3:00 – Closing remarks and optional lab tours

1:15 – 2:00 – Hydrogen infrastructure and regulations, Sunderland2:00 – 2:30 – Short- and- long-term prospects and discussion, Jackson2:30 – 3:00 – Closing remarks and optional lab tours


g pg p

Quick Quiz on EnergyList the three countries with the largest annual oil production in 2009• List the three countries with the largest annual oil production in 2009– Russia, Saudi Arabia, and United States (from Energy Information Agency (EIA)

http://www.eia.doe.gov/)• Name the three largest importers of fossil fuels to the U.S.Name the three largest importers of fossil fuels to the U.S.

– In barrels/yr: Canada (895 M), Mexico (556 M), Saudi Arabia (541 M)

• On average how many barrels of oil are consumed annually per person i th U S Chi d I diin the U.S., China, and India– 22.6, 2.1, and 0.9 respectively (as of 2008 from EIA)

• Rank these primary sources of energy conversion in terms of totalRank these primary sources of energy conversion in terms of total utilization in the world (Natural Gas, Oil, Coal, Uranium, Hydroelectric)– Oil, Coal, Natural Gas, Uranium, Hydroelectric (as of 2006 from EIA)

A i t l h k f hi h ffi i h t lt i• Approximately how many square km of high-efficiency photovoltaicswould it take to provide all of the U.S. electrical power needs?– Reasonable estimates range from 10000 – 14000 km2


Sources and Sinks for Energy Conversion Processes in the U.S.

A th U S d d ti l l f• As the U.S. economy grows, energy demands grows, particularly for transportation

• For U.S. electric power, growth increased demand has been met by getting more out existing nuclear plants g p

– No new nuclear plants have come online since 1990.• kWe*hr per $ GDP has decreased from 3.55 in 1990 to 2.90 in 2002.

Electricity Fuel Source 1949-2007 Total Energy Req’d. by Sector 1949-2007


from Energy Information Agency (EIA): http://www.eia.doe.gov

Where we are today: Identifying the Opportunities

1 Exajoule = 2.77*1011 kWh

Potential for central power SOFC’s with

Potential for distributed power

power SOFC s with carbon capture

distributed power with combined cooling and heating with SOFC’s and PEMFC’sPEMFC s

Potential for H2 derivedfrom non-petroleum sources for PEMFC powered vehicles

from Lawrence Livermore Natl. Laboratoryhttp://eed llnl gov/flow (June 2004)


http://eed.llnl.gov/flow (June 2004)

The Cost of Converting Energy via Combustioninto Useful Work or Heat

• Steady increase in CO2 emissions has lead to a relatively rapid rise in CO2concentrations in atmosphere

This increases absorption of long wave– This increases absorption of long-wave length radiation from the earth.

• Methane CH4 in the atmosphere is rising at a faster fractional rate– CH4 is approximately 25X worse than CO2

for absorbing long-wave length radiation from the earth.

• Other gases are also important such• Other gases are also important such as N2O (>100X worse than CO2) and refrigerants CFC’s

• Particulate matter effects not known

• What are engineering solutions that can abate the increase?


– It is almost impossible to reverse it.

Climate change is a long-term strategic problem with implications for today

from A Janetos Joint Global Change Research Institutefrom A. Janetos, Joint Global Change Research Institute

Fossil Fuel Carbon

20

per Y

ear

Historical EmissionsGTSP 750 Fossil Fuel Carbon

EmissionsHistoric & 2005-21001750-2005 300 GtC

15

mis

sion

s G

igat

ons GTSP_750

GTSP_650GTSP_550GTSP_450GTSP Reference Case

GTSP Ref 1430 GtC

750 ppm 1200 GtC

650 ppm 1040 GtC5

10

sil F

uel C

arbo

n E

m

550 ppm 862 GtC

450 ppm 480 GtC-

1850 1900 1950 2000 2050 2100 2150 2200 2250 2300

Glo

bal F

oss

• Stabilization of greenhouse gas concentrations is the goal of the Framework Convention on Climate Change.

• Stabilizing CO2 concentrations at any level means that global, CO2


g 2 y g , 2emissions must peak and then decline continuously.

Suggested Global Warming Abatement Strategies For Stationary Electric Power Generation

• Refocus our stationary electric power generation

• Increased use of nuclear power plants– Use of fuel enrichment for higher energy utilization from Uranium– Use of fuel enrichment for higher energy utilization from Uranium

• Security risks– Loss of infrastructure and political will in U.S. and other countries

• The hopeful development of fusion energy productionp p gy p– Slow progress and the promises of ITER – an international fusion collaboration

• Adaptation of more renewable energy sourcesWind power ocean current power– Wind power, ocean current power• Low energy density and only locally consistent in some regions

– Solar energy conversion• Limits of photovoltaics and not always reliable sourceLimits of photovoltaics and not always reliable source

– Biomass conversion• Questions about ability to replenish soil and avoid energy-demanding

fertilizers and best use of land resource


Suggested Global Warming Abatement Strategies For Stationary Electric Power Generation

• Continue use of fossil fuels while reducing CO2 emissions

• CO (or carbon) sequestration in deep oceans or underground storage• CO2 (or carbon) sequestration in deep oceans or underground storage– High energy costs and risks associated with pumping CO2

• Importance of separating O2 from air to decrease losses– Increase utilization of advanced “clean coal” technologyIncrease utilization of advanced clean coal technology

• Reduce overall work demands for energy conversion– Improved efficiency of buildings and industrial processes

U f di t ib t d ti d f t h t• Use of distributed power generation and recovery of waste heat– Social adjustments and use of policy to drive them

• Movement away from growth as the primary marker for economic success


Suggested Global Warming Abatement Strategies for Transportation Power Needsp

• Reducing the dependence of transportation on oil– Make fuels from CO2 captured from the environment– Making fuels from biomass (preferably not food sources)g ( y )

• Adaptation of fuel cell and H2-powered vehicles – Challenge of cost and resources

• Pt loading of catalysts• Pt loading of catalysts– Challenge of changing fuel infrastructure for H2 delivery and storage

• Implementation of electric vehicles– Limitations of batteries, the consumers, and the automotive market– Environmental questions

• Improving efficiency of conventional vehiclesImproving efficiency of conventional vehicles– Hybrid electric vehicle technology– Increased use of diesel engines

• How far does this take us in addressing the problem


g p

Why and Why not Hydrogen for Transportation?• Hydrogen like electricity is an energy carrier not an energy supply

– Unlike electricity, it can be stored though not easily.• Energy densities are too low and storage requires high pressures or low

temperatures.• Fuel Cells: a historical driver for H2

– Low temperature fuel cells have needed pure H2 (<100 ppm CO) for higher power density (approach 1 kW/liter of fuel cell, longer life (> 5000 hrs.)

P t E h M b (PEM) f l ll f t t ti ill di t t th• Proton Exchange Membrane (PEM) fuel cells for transportation will dictate the needs for H2 infrastructure (leaders – Ballard, GM, Honda, UTC)

• Hydrogen is clean and can be produced from several sourcesFossil fuels with easier CO sequestration– Fossil fuels with easier CO2 sequestration

– Solar power with electrolysis or high-temperature thermolysis– Nuclear power, wind power, and hydroelectric with high temperature electrolysis

• Competitors synfuels biofuels and battery powered vehicles• Competitors – synfuels, biofuels, and battery-powered vehicles• Current Usages of Hydrogen > 50 million tons/yr & growing

– As a fuel refining agent Ammonia production


– Ammonia production

Fuel Cells and H2 in Transportation News: Nation• DOE (Sec’y Chu) has proposed cutsDOE (Sec y Chu) has proposed cuts

in EERE Fuel Cell program from $179 M in FY10 to $100M in FY12– Strongly questioned by many: Toyota,

Honda FCXClarity

g y q y y y ,GM, Daimler and other manufacturers

– 1500 at H2 Program review this May• California continuing with Fuel Cell

GM Equinoxg

Partnership program– 26 H2 fueling stations in CA– Goal is to have commercial vehicles in

2017• Car manufactures state in May 2010

that they are still wanting to stick to 2015 commercialization goal– H2 storage and distribution still

acknowledged as challenges

ISE Ultra-E™ 500 Bus35kW battery pack75 or 150 kW Ballard HD6 Si ELFA™ M t


– Fuel cells are approaching all performance goals

Siemens ELFA™ Motors

Fuel Cells and Hydrogen in Recent News: Globe• European Union increased funding• European Union increased funding

on H2 program in 2010 to € 94 M with hopes of commercializing cars in this decadedecade

• Japan Hydrogen Highway for fuel cell vehicles with stations in 11 cities. METI in Japan still moving toward

Wärtsila and Topsoe Fuel Cell 50 and 250 kW solid oxide fuel cell METI in Japan still moving toward

commercialization in 2015 of fuel cell vehicles.– Hydrogen stations run on reformed natural

systems

y ggas

• Denmark becoming leader in stationary fuel cell for CHP

Shell HydrogenIceland Program

– Partly seen as means of balancing wind power fluctations.

• Many successful fuel cell bus demo


programs outside of U.S.

Fuel Cells and H2 in Stationary Power News: Nation• DOE has identified early markets for fuel cells which• DOE has identified early markets for fuel cells which

are either commercially viable or almost so– Hybrid forklifts for warehouse applications in combination with

local H2 generationlocal H2 generation– Back-up power for cell phones and other applications– Stationary power for critical supplies

• Military fuel cell applications have led to many recent Hybrid PEM Fuel Cell /• Military fuel cell applications have led to many recent increases in DOD fuel cell applied R&D– Underwater unmanned vehicles (UUVs)– Portable gensets operating on portable fuels

Hybrid PEM Fuel Cell / Battery Fork Lift

– Portable gensets operating on portable fuels• Other applications may also be viable and fundable

through other meansCHP or CCHP for both residential and commercial applications– CHP or CCHP for both residential and commercial applications

– Building power in regions with high electric costs (> 10¢/kWh)• Motorweek Video


DOE EERE Fuel Cell Program Vision

DOE’s Hydrogen Analysis Center


http://hydrogen.pnl.gov/cocoon/morf/hydrogen/article/103

Components of a Single Electrochemical Cell(one of many in a fuel cell stack)

Current CollectorCurrent Collector(low electrical resistance, cooling passages, inexpensive)

Anode flow path(channels for current flow, integrated with current collector)( g )

Anode gas diffusion layer(low electrical resistance, porous for gas distribution)

Anode catalyst layer (H2 oxidation)(i i i h b i i i l l di )(intimate contact with membrane, resistant to poisoning, low loadings)

Ionic Membrane (H+ or O2- or CO32- transport)

(intimate contact with electrocatalysts, resistant to poisoning)

Cathode catalyst layer (O2 reduction)Cathode catalyst layer (O2 reduction)(intimate contact with membrane, resistant to poisoning)

Cathode gas diffusion layer(low electrical resistance, porous for gas, hydrophobic for low temperature fuel cells)

Cathode flow path(low electrical resistance, porous for gas distribution)

Current Collector


Different Types of Fuel Cells and Their Overall Electrochemical Reactions

• Proton Exchange Membrane (Nafion - polymer): 60 to 180 °C, 1 to 5 atm.– at the anode, H2 → 2H+ + 2e-

– at the cathode, 0.5 O2 + 2H+ + 2e-→ H2O• Direct Methanol Fuel Cell (Nafion): 70 to 100 °C, 1 to 5 atm.

– at the anode, CH3OH + H2O → CO2 + 6H+ + 6e-

– at the cathode, 1.5 O2 + 6H+ + 6e-→ 3H2O• Solid Oxide (stabilized ZrO2): 600 to 1000 °C, 1 to 8 atm.

– at the anode, H2 + O2- → H2O + 2e- and CO + O2- → CO2 + 2e-

– at the cathode, 0.5 O2 + 2e-→ O2-

• Phosphoric Acid (H3PO4): 190 to 220 °C, 1 to 8 atm.– at the anode, H2 → 2H+ + 2e-

– at the cathode, 0.5 O2 + 2H+ + 2e-→ H2O• Molten Carbonate (LixM1-xCO3): 650 °C, 1 to 3 atm.

– at the anode, H2 + CO32-→ H2O + CO2 +2e- and CO + CO3

2-→ 2CO2 +2e-

– at the cathode 0.5 O2 + CO2 + 2e-→ CO32-


Fuel Cells and Hydrogen: Further Thoughts• U S Department of Energy committed to fuel cells for small scale• U.S. Department of Energy committed to fuel cells for small-scale

applications – some fueled with hydrogen (forklifts) and others with hydrocarbons (distributed power, truck APU’s)

• Long term investment in H in the U S is less clear than in Japan and• Long-term investment in H2 in the U.S is less clear than in Japan and Europe at the moment and still depends on government leadership– Does California replace the federal government as the leader?

• Successful fleet vehicle demonstration programs with managed H• Successful fleet vehicle demonstration programs with managed H2fueling supplies may not have unreasonable operational costs, but will have large capital costs.

e g Vancouver 2010 Olympics– e.g., Vancouver 2010 Olympics• Fuel cell and hydrogen industry oversold progress in late 90’s and

early part of this decade and slow commercialization turned away investorsinvestors.– Are high-tech battery manufacturers doing the same today?

• It is critical for policymakers be informed in making decisions for both short term economics and long term sustainability


both short-term economics and long-term sustainability.

Agenda for Seminar9:00 – 9:15 – Introduction from Univ. of Maryland Energy Research Center,9:00 9:15 Introduction from Univ. of Maryland Energy Research Center,

Prof. Eric Wachsman, Director9:15 – 9:45 – Our current energy infrastructure and potential for hydrogen and

fuel cells, Prof. Greg Jackson9:45 – 10:05 – Review of alternate fuels, advanced technology vehicles and

prospects for hydrogen, Chris Rice, Maryland Energy Administration, Prof. Jackson


cells , Jackson10:45 – 11:15 – Hydrogen production, storage, and distribution, Jackson11:15 – 12:00 – Hydrogen safety and fire hazards, Prof. Peter Sunderland12:00 – 1:15 – Lunch and GM Fuel Cell Equinox Ride‐N‐Drive1:15 – 2:00 – Hydrogen infrastructure and regulations, Sunderland2:00 – 2:30 – Short- and- long-term prospects and discussion, Jackson2:30 – 3:00 – Closing remarks and optional lab tours


2:30 3:00 Closing remarks and optional lab tours

Fueling Our Transportation Sector toward Sustainability: Why not H2 Fuel Cells?

3.0

Greenhouse Gas Pollution (Light duty vehicles only) (Billion/ tonnes CO2-equivalent/year) 100% Gasoline

ICEVs

2.0

2.5 Base Case:Gasoline HEV

Scenario

1 0

1.51990 LDV GHG

Ethanol PHEVS i

Gasoline PHEV Scenario

0.5

1.0

GHG Goal: 60% below 1990 Pollution

GHG Goal: 80% below 1990 Pollution

Scenario

from Sandy Thomas using Argonne National Laboratory GREET 1.8a

-

2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Pollution

FCV Scenario


Well-to-Wheel Analysis of Advanced Vehicles• Wang (2007) GREET Well-to-Wheel analysis of plug-in hybrids• Analysis includes well-to-pump (WTP) and pump-to-wheel (PTW)

Total greenhouse gas emissions for WTW of various plug-in hybrid vehicles assuming

T t l f

California electric supply

Total energy for WTW of various plug-in hybrid vehicles assuming C lif i l t iCalifornia electric supply


A DOE H2 Program Perspective on Alternative Vehicles (Satyapal 2011)


Components of Fuel Cell Vehicles

• Fuel cell vehicles are electric vehicles but with the potential for much further range than battery-powered vehicles.

• 430 mi range on 156 liter H2 storage tank at 70 MPa (Toyota in California 2009)

• 53-59% efficient based on H2 for typical drive cycle (DOE EERE)


Proton Exchange Membrane Fuel Cell Architecture

• Acidic polymer electrolytes (25-100 µm thick) conduct H+ (or H3O+) ions from anode to cathode– Nafion electrolytes require

hydration and thus low-temperature operation.

• Carbon paper provide porous media for gas p gtransport to active catalyst layer for electrochemistry

• Precious metal catalyst for• Precious metal catalyst for H2 oxidation at anode and O2 reduction to H2O at cathode Image from


cathode Image from http://www.ballard.com/About_Ballard/Resources/How_Fuel_Cells_Work.htm

Understanding Voltage (Polarization) Losses in PEM Fuel Cells

Eo, Nernst

• Voltage losses results in heat released in fuel cell which can be used to heat reactants, provide hot water, or other heating application.

Crossovers and shorts Eo, experiment

Total Cell Resistances

Contact CablesMembrane ionic Contact resistances

CablesCathode Overpotential

Anode Overpotential

Diff i it d l di

Cell Voltage (V)

Mass Transport

Diffusivity under landings (2D/3D)

Diffusivity through GDL (1D)

Catalyst Diffusivity

Fast Transient Polarization

O2 depletion at outlet

Current Density (A/cm2)


from Pat Hearn, Ballard Power Systems

Why not Onboard Fuel Processing of Liquid Fuels?

L t t N fi b d PEM f l ll t l i d b• Low-temperature Nafion-based PEM fuel cells are strongly poisoned by CO and therefore require H2 clean-up as well as a fuel reformer.

• However efforts are ongoing to look at nanostructured catalysts that ld i CO t l & t bilitwould improve CO tolerance & stability

Anode core-chell electrocatalystTcell = 70 ºC, P = 3.0 bar, Fuel Stoich. = 2.2

Commercial TKK PtRu anodeAnode core chell electrocatalystcreated in situ from PtSn intermetallic – no organic stabilizers reduces impact on catalyst/ionomer interface

Commercial TKK PtRu anode electrocatalyst used for CO tolerance

on catalyst/ionomer interface


Stack efficiency: FC

Efficiency of PEMFC System with PROx CO Clean-up

combHinFCH

cellcellcellsFC hm

iVAn

,2,,2

Balance of Plant Fuel Processor

efficiency: BOP

lostcellcellcellsBOP

WiVAn

and H2 Purifierefficiency: FP

cellcellcells

BOP iVAn

combfuelinFPfuel

combHinFCHFP hm

hm

,,,

,2,,2

cellcellcells

lostcellcellcells

combHinFCH

cellcellcells

combfuelinFPfuel

combHinFCHBOPFCFPth iVAn

WiVAnhmiVAn

hmhm

,2,,2,,,

,2,,2


ff ,,,,,,

• High-temperature PEMFC MEA’s

High-Temperature PEMFC Testing and CO ToleranceHigh-temperature PEMFC MEA s provide high CO tolerance by operating at temperatures above 150 °C– H3PO4 –doped polymer electrolytes

require no humidification to transport H+ ions across membrane

– Operation at 160 -180 ºC permits 2%Operation at 160 180 C permits 2% CO tolerance

– Power densities and Vcell much lower than Nafion-based PEM fuel cells

– Higher stack costs with high loadings approaching 1.0 - 2.0 mg/cm2

• Long-term stability issues remain d d d i t idiand depends in part on avoiding

condensation in the MEA.


PEMFCs in the News• Plug Power developed Gensys system for small-scale CHP: high-temperature

(160 180 ºC) PBI based PEMFC system running on natural gas reformate at(160-180 ºC) PBI-based PEMFC system running on natural gas reformate at ηelec = 30% and ηCHP = 85% – Inadequate costs and durability ($10000/kWe at currently 2000 hrs durability)

B ll d P S t ith th d l i B ll d’ FC G 1300 f• Ballard Power Systems with others developing Ballard’s FC-Gen 1300 for back-up power in Asian markets (India)– up to 3 kWe powered by natural gas or LPG, ηelec > 30%

http://www plugpower com/userfiles/file/GenSysHT 03 09 pdfP l (DOE) 2010


http://www.plugpower.com/userfiles/file/GenSysHT-03-09.pdfPapageorgopoulos (DOE) 2010

Solid Oxide Fuel Cell Architecture

• Thin (10-20 µm) O2- conducting electrolytes provide oxidizer from cathode to anode

• Thick (500-1000 µm) anode structures for mechanical integrity of cells

• Porous composite electrodes for gas transport to electrochemically active region near electrolyte membrane and for electronic current collection

• Pre-electrochemical reactions in porous anode to convert hydrocarbon feeds (such as light oil-well gases) into wanted (H2/CO) and unwantedinto wanted (H2/CO) and unwanted (surface C) products

from Kee, Zhu, Sukeshini, and Jackson 2008


from Kee, Zhu, Sukeshini, and Jackson 2008

VV

Voltage – Current Relationships in Fuel Cells

VOCV – reversible Nernst potential difference at concentrations in

cOaHreac

OCV ppp

FRT

FGV

2/1,2,

02ln

22

cconc,cact,ohmaact,aconc,reversiblecell,cell VV

22 cmAmpsV

cmW

cell difference at concentrations in channel flow

conc,a, conc,c – overpotential due to loss in concentrations to

aOHpFF ,2

22

O,aH,a,eH

O,a,eH,aHconc,a pp

ppFRTη

22

22ln2

1 2

Voltage vs. current densityfor SOFC with typical porous electrode

cmcm

to loss in concentrations to drive transport to the functional layer in both electrodes

– overpotential at

22

,c,eO

,cOconc,c p

pFRTη

2

2ln4

0.8

1

1.2

anode

VOCV

cathode

act,a, act,c – overpotential at electrocatalyst / electrolyte interface to drive electrochemical reactions

TRnF

TRnF

ii actractf expexp0

0.4

0.6Vo

ls p

er c

ell

ohmic

Tcell = 800 °C@ 25% syngas conv.

ohm – overpotential due to electrolyte resistance to ion transport and electrode

bulk,cbulk,abulk,eOhm RRRiη 0

0.2

0 0.5 1 1.5 2 2.5 3

V

/ 2 f

P H2,anode = 0.23 barP CO,anode = 0.19 barP O2,cathode = 0.18 bar


transport and electrode resistance to e- transport. Amp/cm 2 of membrane

Comparison of Fuel Cell Stack Technology• Proton Exchange Membrane Fuel Cells • Solid Oxide Fuel Cellsg

– Operation at low temperatures < 120ºC– Expensive precious metal catalysts– Fuel limited to relatively pure H2 with inert

– Operation at high temperatures > 600ºC– Energy intensive fabrication processes– Potential for direct fueling – coal gas, NG, y p 2

diluents for high power density applications– H2O management critical for most designs

• PEMFC applications – vehicles, f f

ethanol, biogas– Readily integrated with gas turbines for

high efficiency hybrid plants

SOFC applications small centralforklifts, small gensets, portable power • SOFC applications – small central power, distributed power, APU’s

Delphi, 3.4 kW SOFC system efficiency ≈ 38%operating on nat gas (FC Sem 2007)

Ballard Power System stack (liquid cooled d i 8 kW t 55% t k ffi i )


operating on nat. gas (FC Sem. 2007)producing ~ 8 kW at ≈ 55% stack efficiency)

Small Hydrocarbon-fueled SOFC Systems

from Bob Kee, Colorado School of Mines


SOFCs in the News• SOFCs for distributed power: Wärtsilä & Topsoe Fuel Cell natural-gas andSOFC Volume Production Costs: Vora (DOE) 2010• SOFCs for distributed power:

Wärtsilä/Topsoe Fuel Cell– Diesel engine OEMs like Wärtsilä

are partnering with SOFC

Wärtsilä & Topsoe Fuel Cell natural gas and bio-gas fueled SOFC units for 20-50 kW

SOFC Volume Production Costs: Vora (DOE) 2010

are partnering with SOFC manufacturers for distributed power systems

– Efficiencies with natural-gas fueledEfficiencies with natural gas fueled systems > 50%

5 kW SOFC APU – Diesel-Fueled from Delphihttp://delphi.com/manufacturers/cv/fuelcells/

• SOFCs for truck APU Delphi– 35% efficiency with overall system

power density approaching 12 W/l– Start-up time – 120 min.– Durability -- ~ 5000 hrs.– ~$700/kW


High Power Density Intermediate-Temperature SOFC Development (Wachsman)

ESB/GDC

GDC• Integrating new materials and

microstructures to achieve unprecedented performance and reduce SOFC costs dramatically

J. S. Ahn, D. Pergolesi, M. A. Camaratta, H. Yoon, B. W. Lee E Traversa and E D Wachsman Electrochem

reduce SOFC costs dramatically

• Approaching 40 W/cm3 and 10 kW/kg with H2 fuel at the stack level and red cing the cost of sealing and


Lee, E. Traversa and E. D. Wachsman, Electrochem. Comm., 11, 1504 (2009).

reducing the cost of sealing and housing materials.

Complexity of Centralized SOFC Coal-Fueled Power Plant


from Williams et al. SECA program (2007)

Feasibility of SOFC Hydrocarbon-Fueled Auxiliary Power Unit

from Scheffer , Delphi, Fuel Cell Seminar 2007


SOFCs for Stationary Distributed PowerSOFC f di ib d (Bl Images from http://www bloomenergy com• SOFCs for distributed power (Bloom Energy)– $9000/kW current cost is not marketable

Images from http://www.bloomenergy.com

– Steady-state application (for support power)

– “reversible” power plant concept – fuel production or fuel utilizationproduction or fuel utilization

• Bloom energy uses robust electrolyte supported designs

Not high power density– Not high power density– Working trade-offs between system cost

and material costs– Current price according to news

Electrochemical cell from Bloom Energy

Current price according to news • Initial costs $7000/kW more than 10X

too high• Marketable with subsiders or very high


y gelectric cost as in California 12.8 ₵/kWh

Making H2 for Fuel Cells: Possible Pathways95% of H2 derived from NG

Hydrogen Sources

Liquid Fuels

NaturalGas Biomass Water

Electrolysis

F l

from Santosh Limaye (2005), consultant for Oak Ridge Natl. Lab

Hydrogen Partial Autothermal Steam Fuel

Fuel Treatment

Sulfur Removal

Fuel Refinement

g

95% of H2 produced today,efficiency between 70-80%

Hydrogen Separation

Partial Oxidation

Autothermal Reforming

Steam Reforming

Fuel Decomposition

Hydrogen Membrane PSA Electrochemical Preferential

Electrolysis

C iy g

PurificationMembrane Technology

PSATechnology

Electrochemical Separation

Preferential Oxidation

Hydrogen Pipeline Distributed

G iOn-Demand G i

Truck Delivery LH

Cryogenics

DistributionPipeline Generation GenerationDelivery LH2

Hydrogen Storage

Compressed Container

Cryogenic Liquid

Metal Hydride

Chemically Bound

Carbon Nanotubes


Storage Container Liquid Hydride Bound Nanotubes

Sustainable Paths to Hydrogenfrom John Turner, NREL 2006

Solar Energy

Heat Biomass

Mechanical Energy

Electricity Conversion

H drogen

Thermolysis Electrolysis Photolysis


Hydrogen

Fuel Cells for Cars: Well to Wheel Issues

F l• GREET Model from Argonne Natl. Lab

for Well to Wheel analysisFuelSupply

F lfrom Santosh Limaye (2005),

for Well-to-Wheel analysis

FuelProcessor

H dΔH

Exhaust

consultant for Oak Ridge Natl. Lab

HydrogenClean-UpCombustor

Hydrogen

ΔH<5 ppm CO

F l C ll

HydrogenStorageAir

Oxygen

WasteCO, CO2, H2, N2, H2O

E h Fuel CellOxygenEnrichment

Exhaust

Exhaust

Other Thermal & Water Management Systems not shown


Other Thermal & Water Management Systems not shown

Purifying H2 for Portable PEM Fuel Cells

• Pd Membrane system evaluation– Promise of very thin (< 2 µm) Pall Corporation technology– Validated model used to assess design of next generation system with anode g g y

recirculation

• PROx-based system evaluationN d f i d CO l ti it ith h h d b f l d t– Need for improved CO selectivity with heavy hydrocarbon-fueled systems

– Simpler system but changes in heat exchanger configuration required– Importance of defining requirements for reformate tolerant stack

• Current system-level modeling of PROx system is ongoing and will be compared with past-reported calculations of Pd-membrane system

• Uncertainty of how high-temperature PEM membranes will impact analysis


St f 4 0k f H d 60k h ( l t i )

Storing H2 for Portable and Distributed Power

Composite Cylinders @ 700 bar

Commercial Gas Cylinders @ 180 bar

Diesel Fuel + Reformer

Storage of 4.0kg of Hydrogen = 60kw-hrs (electric )

@ 700 barCylinders @ 180 bar

Diesel Fuel

50 kg Total Wt 3

87 kg Total Wt

46 L ( 1.6 ft3)

87 kg Total Wt 166 L (5.9 ft3)

390 kg Total Wt 340 L (12 ft3)


Catalytic Fuel Reforming of Natural Gas to Make H2

• Endothermic Steam Reforming (SR)Endothermic Steam Reforming (SR)–Gives highest concentration of H2 out (up to 70% H2)

CH4 + H2O + 20.6 kJ/gmol → CO + 3H2Heat must be added indirectly usually by burning fuelHeat must be added indirectly, usually by burning fuel.

CH4 + 2*O2 → CO2 + 2*H2O + 80.2 kJ/mgolWater-gas shift drives further H2 production

CO + H O CO + H + 4 1 kJ/mgolCO + H2O ↔ CO2 + H2 + 4.1 kJ/mgol

• Thermally Neutral Auto-thermal Reforming (ATR)CH4 + ½O2 + ½H2O → CO2 + 2½H2 +19 8 kJ/gmolCH4 + ½O2 + ½H2O → CO2 + 2½H2 +19.8 kJ/gmolCO + H2O ↔ CO2 + H2 + 4.1 kJ/gmol

• Exothermic Partial Oxidation (POx)– Gives lower concentration of H2 out due to N2 dilution from air

CH4 + O2 = CO + 2H2 + 31.9 kJ/gmol

All H t f ti t 300 KUniv. of Maryland Energy Research Center

College Park, MD

All Heats of reaction at 300 K

H2 from Steam Gasification of CoalPerformance of Dry Ash Gasifier (Higman and van der Burgt 2003)

• Lurgi Dry Ash Gasifier Performance

Coal Type Lignite Bituminous Anthracite

C wt % 69.5 77.3 92.1

H wt % 4.9 5.9 2.6

S wt % 0.4 4.3 3.9S t % 0 3 3 9

N wt % 0.8 1.4 0.3

O wt % 24.4 11.1 1.1

Feed Components

Coal kg % 40.0 24.3 27.8

H2O kg % 49.8 62.7 54.7

O2 kg % 10.2 13.0 17.5

Raw Gas Effluent

H2 mol % 37.2 42.3 40.7

CH4 mol % 11.8 8.6 5.6

CO mol% 19.7 15.2 22.1

CO + H S mol % 30 4 32 4 30 8CO2 + H2S mol % 30.4 32.4 30.8

C2+ mol% (largely C2H4) 0.4 0.8 0.4

N2 mol% 0.5 0.7 0.4

hcomb (kJ/gmol @ 1000K) 245.5 223.0 211.4


before and after CO2 removal 352.8 329.9 305.4

Clean Coal (?) with CO2 Capture and H2 Production = 65% with 55%• H2 Co-Production with CO2 Sequestration

STACKGASGAS TURBINE

AIR

HRSGSTURBINEEXHAUST

COOLING / HEATH2 TO

HHV = 65% with 55% Coal Energy as H2

GENERATOR

RAWSYN

HUMIDIFIED /PREHEATED

O2HP

STEAM

HOTDEPLETED

AIR

ITM

COOLING / HEATRECOVERY &H2COMPRESSION

H2 TOPIPELINE

H2

GASIFICATION(ATR)

H2SEPARATINGMEMBRANE

SOFC

SYNGASCOAL &

LIMESTONE

ITM

O2 FORGASIFIER &CATALYTICOXIDATION

UNITDEPLETEDFUEL GAS

HEATRECOVERY &

HT GASCLEANUP

HPSTEAM

STEAMTURBINE

CHAR

STACKGAS

CATALYTICCO2

SHIFT & H2SEPARATINGMEMBRANE

H2

O2 FROM ITM

SWEEP GAS

SWEEP

FLUID BEDCHAR BOILER &

STACK GASCLEANUP

HP STEAMAIR

CO2 TOPIPELINE

GENERATOROXIDATION, GASCOOLING & Hg

REMOVAL

COMPRESSION/DEHYDRATION/

PUMPING

GAS


ASH

TOCONDENSER

DOE Projected Near and Long Term H2 Dispensed Costs (Satyapal 2011)


Hydrogen Directly from Renewable Sources?• Renewable energy resources are concentrated far from population centers• Renewable energy resources are concentrated far from population centers

and thus the idea of making H2 locally from renewables requires significant penalty for shipping.− Is it better to ship electrons or H2 or to perform local electrolysis?

from Milbrandt & Mann, NREL 2007


Possible Sustainable H2 (and O2) Supplyadapted from John Turner, NREL 2006

Power Electronics

ElectrolyzerGaseous Hydrogen

Transmission PipelineH2

e-

Electronics p

Energy Storage in Pipeline

H2O

O2 Gaseous Hydrogen

Fuel Market

WindGenerators

Gaseous HydrogenP H2

e-

GW-hrs of energy storage are necessary.

Geologic Storage ???Power Electronics

Electrolyzer

H2O

2

O2

Oxygen Sales to NearbyGasification Plants

WindGenerators

H2O

Univ. of Maryland Energy Research Center College Park, MDBill Leighty, http://www.leightyfoundation.org/earth.php

Challenge of H2 Storage and DistributionR bl H d i f i f• Renewable pure H2 production from a variety of sources now requires means of storing H2 on vehicles or at power sites.

• Current-day technology requires H2 storage as gas in high-pressure it t k ith t 350 t 700 bcomposite tanks with pressures at 350 to 700 bar.

– Safety concerns with high pressures and significant costs for tank– Range of high-end fuel cell vehicles approaching best IC engine cars with

li t hi h tgasoline at highest gas pressure.– Local compression to fill tanks

• Shipping is only easily done in pipelines and such infrastructure is t i lnot economical.

• Local compression to fill tanks can be done quickly but with a substantial pump-to-car inefficiency.

• Possibility of shipping around renewable or nuclear electricity to do electrolysis (need to develop higher efficiency, high-T electrolysis).

• Value of H2 does not need to be in energy efficiency, but in security


and greenhouse gas reductions

DOE Hydrogen Storage Targetsfrom Catherine Grégoire Padró of Los Alamos National Laboratory


Challenge of H2 Distributionadapted from Catherine Grégoire Padró of Los Alamos National Laboratory

• Some H2 distribution and delivery infrastructure exists today– Distributed generation from natural gas reforming– Commercial delivery as liquid or compressed gas– Commercial delivery as liquid or compressed gas– 200+ miles of H2 pipeline primarily in Gulf Coast for petroleum and other

chemical processes • What will it take to expand H2 infrastructure?What will it take to expand H2 infrastructure?

– Costs for building natural gas steam reforming supply in 100 largest metropolitan areas and along every interstate range from $12B up to $100B+• Not long-term solution but transition technology to renewable sources for H2

.Not long term solution but transition technology to renewable sources for H2

– Auto companies and energy companies want each other to step forward first and hence the chicken-egg dilemma remains.


CO2 Penalties for H2 Deliveryfrom C. Grégoire Padró of Los Alamos National Laboratory


Fuel Cell Industry Perspective:Ballard Power Systems: Markets for PEM Fuel Cells

Automotive Fuel Cell Cooperation (AFCC) is a private company owned 50.1% by Daimler,

30% by Ford, and 19.9% by Ballardhttp://www ballard com


http://www.ballard.com

PEM Fuel Cells –Challenges and Breakthroughs• Vehicular fuel cell system development has brought this technology to some• Vehicular fuel cell system development has brought this technology to some

maturity but costs remain high even for mass production ($75 - $100/kW)

• Markets with high kW costs provide best opportunities for todayFork lifts portable generation telecom back up APU’s electronic devices– Fork lifts, portable generation, telecom back-up, APU s, electronic devices

• What are the barriers– Cost (precious metal catalyst and

expensive polymer membrane) Ballard Cost Targets through 2010 for PEMFC Stacksexpensive polymer membrane)– Storing pure H2 supply – Systems issues (H2O management,

storing pure H2 or processing fuel)

Ballard Cost Targets through 2010 for PEMFC Stacks

g p 2 p g )

• What are forward looking solutions– Reduced precious metals – Higher temperature membranesHigher temperature membranes– More efficient H2 purification– Light materials for H2 storage


SOFC’s – Identifying Technical Challenges and Breakthroughs

• Stationary power SOFC development funded by DOE has led to one realization, but further funding for small-scale power has led to new technology.– Fabrication costs remain high for SOFC’s (~$175/kW) but have fallen significantly.– Operational cost benefits from very high efficiencies (>60% with hybrid gas

turbine/SOFC’s) and possible cogeneration. • Markets with high fuel costs and steady operation – military power generation,

auxiliary power units and distributed power provide best opportunitiesauxiliary power units, and distributed power – provide best opportunities– Materials issues to be resolved for improved fuel flexibility and operability

• What are forward looking solutions• What are forward looking solutions– New lower-temperature ceramic membranes– Electrocatalyst layers with fuel flexibility

and durabilityand durability– Improved integration for distributed

power load following– Integration with small turbines for high


Integration with small turbines for high efficiency

Solid Oxide Fuel Cell – Challenges Going Forward• Materials still must be optimized for preferred operability• Materials still must be optimized for preferred operability

– Limitations of Ni/YSZ anodes and alternatives – Improved cathodes for lower O2 reduction overpotentials– Finding stable electrolytes for intermediate T ll (< 600 °C) operationFinding stable electrolytes for intermediate Tcell ( 600 C) operation

• Developing less expensive and more reliable fabrication strategies– Current designs require energy intensive / expensive approaches

• Implementing design models for optimizing micro-architecture, heat transfer, and other key aspects of an SOFC fuel cell stack– for high power density and high efficiency– for effective fuel utilization and CO2 sequestration

• Development of surface species thermodynamics and chemistry for fuel cells remains a challenge for kinetically sensitive problemsfuel cells remains a challenge for kinetically sensitive problems – Oxidation of carbonaceous fuels on preferred anode materials– Minimization of losses and stability of cathode materials


Frost et al., Ceramatec, Fuel Cell Seminar 2007

Fuel Works Consortium at UMD• UMD has established, with founding D l t fUMD has established, with founding

support from Ballard Power Systems, the FuelWorks Consortium for fuel processing for fuel cell systems th h i d t i l d t

Development of simulation tools

for system design

through industrial and government support.

• FuelWorks will provide venue for collaboration across ind stries in Advances in liquid collaboration across industries in addressing research needs for hydrocarbon/biofuel friendly fuel cell systems for distributed and mobile

qfuel reforming and H2

purification

Integration of Fuel Processors with Fuel Cells for Systemsy

power applications.Nano-structured catalysts for improved CO oxidation or fuel stack CO tolerance

with Fuel Cells for Systems

Improved impurity tolerance of PEMFC

stacks


Closing Thoughts: Perspective on Fuel Cells• Fuel cell stack costs have dropped dramatically in the past decade but

– Stacks costs remain high for SOFC’s (~$175/kW) and for PEMFC’s (~$60/kW) but have fallen enough that high balance of plant and/or fuel processor costs may not be prohibitive for some key markets including

Di t ib t ith CHP b k• Distribute power with CHP, back-up power• Truck APU’s• Urban bus fleets

M t i l h dli• Materials handling.• Materials advances in areas like high-temp PEMFCs (150 to 200 °C) and

lower-temperature SOFCs (500 to 650 °C) are needed for these promising technologies to provide adequate durability and cost effectiveness totechnologies to provide adequate durability and cost effectiveness to perhaps open up broader markets.

• Some available fuels (such as ethanol) may be very favorable for fuel cell power plants

• Government need not be the only source of funding for these nearer term markets.

• Government is still needed to drive the infrastructure and long-term i t t d d f H hi l d H d ti f bl


investment needed for H2 vehicles and H2 production from renewable energy.

Closing Thoughts: Stationary Fuel Cells• The drop in fuel cell stack costs and the increase in durability has really

opened up the possibility of economically viable natural-gas powered fuel cell systems for buildings and process industries.– Targeted system costs for natural gas fueled systems for PEMFCs are on the

order of $600/kW for < 10 kWe fueled on natural gasorder of $600/kW for < 10 kWe fueled on natural gas. • CHP and even CCHP opportunities exist in govt. funded demonstrations, but

commercial viability may be accessible through thoughtful investment and smart engineeringg g– Combining fuel cells with

• Desiccants (e.g. supermarkets)• Absorption chillers? (e.g., apartments or portable buildings)• Process steam (e.g. food processing)• Hot water heating (e.g. residential

• Auxiliary power (RV’s, airports, and large trucks) and back-up power are facilitated by fuel cell friendly fuels that can be handled cost effectively infacilitated by fuel cell friendly fuels that can be handled cost effectively in upstream fuel processing (propane, ethanol, methanol, and bio-butanol).

• High-temperature PEMFCs (150 – 200 °C) and low-temperature SOFCs (500 –650 °C) may really improve costs in stationary systems, but durability issues


) y y p y y , ymust be resolved either through controls or materials advances.

Fuel Cell Related Research Efforts at UMD• Solid Oxide Fuel Cells (ceramic electrolytes operating at T > 500 °C)• Solid Oxide Fuel Cells (ceramic electrolytes operating at T > 500 C)

– Microfabricated anodes for probing fuel oxidation process using electrochemical characterization, in situ surface spectroscopy, and isotopic tagging

– Thin-film ceria electrodes for evaluating ceria-based anodes for hydrocarbon– Thin-film ceria electrodes for evaluating ceria-based anodes for hydrocarbon oxidation

– SOFC architectures and design models for operation on oil-well off-gases– SOFC-combustor integration for electric combustor in propulsion applicationsSOFC combustor integration for electric combustor in propulsion applications

• PEM Fuel Cells (polymer electrolytes operating at T < 200 °C)PEM fuel cell integration with hydrocarbon fuel processing for portable power– PEM fuel cell integration with hydrocarbon fuel processing for portable power

– Nano-architectured catalysts/electrocatalysts for improved CO tolerance


High-Temperature Fuel-Flexible Solid Oxide Fuel CellsProfs. G. Jackson and B. Eichhorn

• Micro-fabricated electrodes and micro-scale surface characterization provide new understanding to design solid oxide fuel cell assemblies for operating on hydrogen, bio-derived fuels, and fossil fuels

• System design tools being developed to explore how solid oxide fuel cells can be used for making CO2 capture more feasible.

Micro-fabricated fuel cellOptically accessible rigs ExperimentallyMicro fabricated fuel cell architectures to understand

chemistry of H2 and other fuels

Optically accessible rigsfor laser diagnostics to evaluate new materials

Experimentallyvalidated models

for fuel cell design


Exploring Down-the-Channel Performance of SOFC’s Operating on Syngas

Detailed MEA models e plore SOFC performance ith s ngas or CH f el• Detailed MEA models explore SOFC performance with syngas or CH4 fuel• Results below are for Ni/YSZ anode-supported cell with 1020 µm thick anode, 10

µm thick YSZ electrolyte, and 50 µm thick LSM/YSZ cathode. Operating conditions – 800 °C and for range of H2/CO feeds at different conversionconditions 800 C and for range of H2/CO feeds at different conversion– for two different micro-architectures to provide design guidance.

g,anode = 0.57, g,anode = 2.4, δutil,anode = 5 µm

g,anode = 0.48, g,anode = 2.9, δutil,anode = 10 µm

0 8

1

1.2

0 8

1

1.2VoltsW/cm2

0 8

1

1.2

0 8

1

1.2VoltsW/cm2

0%33%

0%33%

0 4

0.6

0.8

Volts

0 4

0.6

0.8Watts/cm

2

0 4

0.6

0.8

Volts

0 4

0.6

0.8 Watts/cm

2

33% 33%

84%

0

0.2

0.4

0

0.2

0.4

0

0.2

0.4

0

0.2

0.484%

84%


00 0.5 1 1.5 2

Amp/cm2

0 00 0.5 1 1.5 2

Amp/cm2

0

Low-Temperature Fuel Cells with H2 from Liquid Fuels Prof. G. Jackson, R. Radermacher, and Ballard Power Systems

UMD d B ll d P S t t• UMD and Ballard Power Systems team are developing integrated PEM fuel cell systems with H2 production and purification from liquid fuels for portable generatorsfuels for portable generators.

• Complex system simulation tools are validated by tests on a Ballard-designed 8 kW fuel cell test and further used for design optimization

34%

0 40

0.5050 °C30°C

34%

0 40

0.5050 °C30°CF l C ll

Fuel Recirculation

Anode Purge

_Coolerss

H

TT

P

RPM

Rea

ctor

erfo

r H2

test and further used for design optimization.Energy efficiency and Water Balance

as a function of net kW and ambient Temp.

28%

30%

32%

em E

ffici

ency

0 10

0.20

0.30

0.40

r Bal

ance

(g/s

)

30 C10 °C

em E

ffici

ency

28%

30%

32%

0 10

0.20

0.30

0.4030 C10 °CFuel Cell

Gas to Gas Humidifier

CoolerAir

Low-P CompressorRetentateRetentate

Burner

Burner

+TRPM

I

M P

V

T

T

T

P P

P

RPM

T

RPM

Z

WG

S R

Pd F

ilte

RPM

22%

24%

26%Syst

e

-0 20

-0.10

0.00

0.10

Wat

er

Syst

e

22%

24%

26%

-0 20

-0.10

0.00

0.10

Sulfur Adsorber

DI FilterDI FilterExhaust Condenser

PP

RPM

T T

P

RPM

Critical H2ORecoveryCritical H2O

Demand


22%500 1500 2500 3500 4500

Net Electric Power (W)

0.2022%500 1500 2500 3500 4500

Net Electric Power (W)

0.20FuelFuel RPM

AirHigh-P Compressor

Nanoparticle Catalysis Design for CO-tolerant PEM Fuel Cell Electrocatalyst Optimization

I iti l lt f PRO ith Pt d R• Initial results for PROx with Pt and Ru nanoparticles show that particle architecture influences activity for low-temperature CO and H2 oxidation.

In 50%H2, 0.2%CO, 0.5%O2, Ar balance, Ru@Pt

p 2

• Ru@Pt core-shell nanoparticles outperform pure Pt, Ru, and PtRu alloys.

M@M’ MM’ (1:1) M + M’ monometallic core-shell alloy mixture

In 50%H2, 0.2%CO, 0.5%O2, Ar balance, Ru@Ptnanoparticles show CO and H2 oxidation light-off at lower T than PtRu alloy nanoparticles or Ru + Pt particle mixtures

(Alayoglu, Nilekar, Mavrikakis, & Eichhorn 2008)


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