high performance flexible reversible solid oxide fuel · pdf filehigh performance flexible...

High Performance Flexible Reversible Solid Oxide Fuel

CellJie Guan, Badri Ramamurthi, Jim Ruud, Jinki Hong, Patrick Riley, Nguyen

Minh

GE Global Research CenterMay 16, 2006

Project ID:PDP34This presentation does not contain any proprietary or confidential information

DE-FC36-04GO14351

2

Hydrogen Program Review, 05/16/2006

Overview

• Project start date: October 2004• Project end date: September

2006• Percent complete: 75%

• Barriers addressed– K. Electricity Costs– G. Capital Costs– H. System Efficiency

• Total project funding–DOE share: $1,252,683–Contractor share: $616,993

• Funding received in FY05: $575,198• Funding for FY06: $677,485

Timeline

Budget

Barriers

3


Objectives

• Demonstrate a single modular stack that can be operated under dual modes–Fuel cell mode to generate electricity from a variety of fuels

–Electrolysis mode to produce hydrogen from steam

• Provide materials set, electrode microstructure, and technology gap assessment for future work

4


Approaches

BASELINE

MATERIALS

SELECTION

REVERSIBLE

STACKS

REVERSIBLE

SINGLE CELLS

FUEL FLEXIBLE

REVERSIBLE

ELECTRODES

Conventional

SOFC

Based

Materials

REVERSIBLE

SOFC

DEMO

Planar Design

Metallic

Interconnect

Electrode Supported

Cells Operating

At <800 o C

Reversible

Multifuel Anode

and

Reversible Electrodes

PROGRAM

ELEMENTS

CONCEPTS

COST

ESTIMATE

Assessment of

SOFC Material

Properties Relevant

to Reversible

Operation

Electrode

Configuration

Microstruture

Composition

Catalytic Activity

Thin Electrolyte

Electrode Supported

Cells Made by

Calendering

Half Sealed

Planar DesignAPPROACHES

BASELINE

MATERIALS

SELECTION

REVERSIBLE

STACKS

REVERSIBLE

SINGLE CELLS

FUEL FLEXIBLE

REVERSIBLE

ELECTRODES

Conventional

SOFC

Based

Materials

REVERSIBLE

SOFC

DEMO

Planar Design

Metallic

Interconnect

Electrode Supported

Cells Operating

At <800 o C

Reversible

Multifuel Anode

and

Reversible Electrodes

PROGRAM

ELEMENTS

CONCEPTS

COST

ESTIMATE

Assessment of

SOFC Material

Properties Relevant

to Reversible

Operation

Electrode

Configuration

Microstruture

Composition

Catalytic Activity

Thin Electrolyte

Electrode Supported

Cells Made by

Calendering

Half Sealed

Planar DesignAPPROACHES Technology Analysis

Key challenges:– Performance for cost and efficiency– Low degradation for reliability

Technical focuses:– Reversible electrode modeling– Electrode compositions and

microstructure engineering

5


Cell Configuration

•SOFCs have the flexibility, running under power generation mode and hydrogen production mode•High temperature solid oxide steam electrolysis can lower the electricity consumption

Fuel, CH4, H2, etc.

Oxidant, air.

Power Generation Mode

Load

e

eCH4 + 4O2- → 2H2O +CO2 + 8e-

2O2 + 8e- → 4O2-

Hydrogen Production Mode

e

e

Pow

er

Steam Hydrogen

Oxygen

2H2O + 4e- → 2H2 + 2O2-

2O2- → O2 + 4e-

~60 μm~7 μm

~300 μm

Oxygen Electrode, PerovskiteElectrolyte, YSZ

Hydrogen Electrode, Ni/YSZ

6


Stack Configuration

Oxygen electrodeElectrolyte

Hydrogen electrode

Interconnect (IC)

Cell

Interconnect (IC)

Cell Module Multi-cell Stack

Cell/ICsRepeat units

7


Oxygen Electrode Performance

• Screened several lanthanum strontium manganites (LSM), lanthanum strontium ferrites (LSF), and lanthanum strontium cobalt iron oxides (LSCF) as oxygen electrodes

• Under both modes, electrode performance increases in the order of LSCF>LSF>LSM/YSZ

800C 200 sccm H2 ~50% H2O

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

-3 -2 -1 0 1 2 3

J (A/cm2)

E (V

), U

tiliz

atio

n LSM-1LSM-2LSF-1LSF-2LSCFUtilization

Electrolyzer

Fuel CellSteam Utilization

Fuel Utilization

8


Oxygen Electrode Performance Stability

• Excess performance degradation was observed with LSM/YSZ as the oxygen electrode in electrolysis mode (SOEC) mainly due to electrode delamination

• LSCF and LSF showed better performance stability in electrolysis mode than LSM/YSZ electrode

800 C

0

200

400

600

800

1000

1200

1400

0 20 40 60 80 100

Time (hrs)

ASR

(moh

m-c

m2 )

LSM SOEC

LSM SOFCLSF SOECLSCF SOECLSF SOFCLSCF SOFC

LSM/YSZ Oxygen electrode

Hydrogen electrodeElectrolyte

9


Oxygen Electrode Reversibility

• Vacancy diffusion and activation at the oxygen electrode/electrolyte interface are different for fuel cell mode and electrolysis mode

• Higher current densities can lead to depletion of vacancies at the interface in electrolysis mode

• Experimental data matched well with non-symmetrical vacancy model

Non-symmetrical vacancy model

Non-symmetrical vacancy model

10


Operation Mode Cyclic Ability

• Evaluated cell performance for fuel cell mode alone, electrolysis mode lone, and fuel cell/electrolysis cyclic mode

• Similar degradation in fuel cell (SOFC), electrolysis (SOEC) and cyclic modes (rSOFC) – perhaps enhanced electrolysis degradation

800 C 50%H2O/50%H2

0

100

200

300

400

500

600

700

800

900

1000

0 100 200 300 400

Time (hrs)

ASR

(moh

m-c

m2 )

SOFC

SOEC

rSOFC

11


Hydrogen Electrode PerformanceFuel cell mode

Electrolysis mode

• Higher polarization losses predicted under electrolysis mode mainly due to difference of diffusion

• Thinner electrode and smaller particles preferred

Conditions:T = 800 CFuel = 50/50 H2/H2OActive layer thickness= 16 μmActive layer particle size=0.8 μm

Region I – H2/H2O diffusion and reaction limitedRegion II – Reaction limitedRegion III – Ion conduction and reaction limited

12


• At 800°C, internal reforming kinetic was fast

• CH4 conversion measured (gas chromatography) > 98%, agrees well with thermodynamic prediction

• Thermodynamic calculations defined carbon deposition boundary

Thermodynamic Prediction of Carbon Deposition BoundaryThermodynamic Prediction of Carbon Deposition Boundary

Hydrogen Electrode Internal Reforming

X is the distance from the fuel inlet along the channel and L is the total channel length

13


• Performance (I-V curve) with internal reforming similar to that with 64% H2/36%N2 fuel

• Improved cells efficiency and potential system simplification with internal reforming

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

100 200 300 400 500Current Density (mA/cm2)

Cel

l Vol

tage

(V)

64% H2 - 36% N2

20% CH4 - 30% H2O - 50% N2

Performance with Internal Reforming

14


• LSCF performed better than LSM/YSZ electrode

• Substantial degradation rate reduction achieved with LSCF oxygen electrode in electrolysis mode

• Improved performance with electrode material selection and process engineering

Module Performance Improvement

0.4

0.6

0.8

1.0

1.2

1.4

1.6

-600 -400 -200 0 200 400 600Current Density (mA/cm2)

Cel

l Vol

tage

(V)

Electrolysis Fuel Cell

Baseline Bilayer + Baseline Oxygen Electrode

Supercell Bilayer + LSCF-SDC Oxygen Electrode

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

0 20 40 60 80 100 120Hours in Electrolysis Degradation Test

ASR

(ohm

-cm

2)

Baseline Bilayer + Baseline Oxygen Electrode

Supercell Bilayer + LSCF-SDC Oxygen Electrode

0.1

1

10

100

1000

0 0.5 1 1.5

Electrolysis ASR (ohm-cm2)

% In

crea

se in

Vol

tage

/ 10

00 h

ours

Technology Feasibility Demo

Reduced Cost, Increased Efficiency

Impr

oved

Rel

aibi

lity

Baseline:LSM-1YSZ-Ni

YSZ-Ni microstructure enginnering

Alternative LSM-2Active LSCF

Processing Improvement

Materials and Process Optimization

Commerical Viable

15


Multi-cell Stack Performance

• Built and tested 3-cell stacks under power generation and electrolysis mode for more than 1000 hrs

• Hydrogen production measured and the measured value close to the predicted

• Cell-cell performance variation needs to be addressed

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

-700 -600 -500 -400 -300 -200 -100 0 100 200 300 400 500 600 700Current Density (mA/cm2)

Stac

k Vo

ltage

(V)

Electrolysis Fuel Cell

0.0

0.4

0.8

1.2

1.6

2.0

2.4

2.8

0 40 80 120 160 200 240 280 320Current Density (mA/cm2)

H2

Flow

Rat

e (L

/min

)

Fuel Exhaust H2 Flow Predicted

Fuel Exhaust H2 Flow Measured

16


Future Works

• Demonstrated multi-cell stack operation and assess performance under reversible operating conditions

• Estimate hydrogen production cost ($/kg H2)• Conduct technology assessment and gap

analysis

17


Summary• Oxygen electrode development

–Performance: LSCF>LSF>LSM–“Irreversibility” of oxygen electrode observed, associated with

differences in vacancy diffusion and activation at electrode/electrolyte interface

• Hydrogen electrode development–Internal reforming with Ni-YSZ modeled and demonstrated –Higher polarization loss under electrolysis mode expected, mainly

due to difference of H2 and H2O diffusion

• Module and stack development–Module and stack performance improved by electrode engineering–Initial multi-cell stacks tested and hydrogen generation demonstrated

18


Acknowledgement

This research was supported in part by DOE award DE-FC36-04GO14351. This support does not constitute an endorsement by DOE of the views expressed in the article.

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