Proton Conductor BasedSolid Oxide Fuel Cells

S. Elangovan, J. Hartvigsen, F. Zhao,D. Ramirez, B. Heck, and D. Larsen

10th Annual SECA Workshop

Pittsburgh, PA14 July 2009

Supported by DOE SBIR Grant: DE‑FG02‑06ER84595

Outline

Thermodynamic Analysis Shows Higher Efficiency for

Proton Cells compared to Oxygen Cells

Stability addressed by the use of composite electrolyte

Anode supported composite electrolyte cell shows

good performance

Stability in high CO2 containing fuel demonstrated

2

Thermodynamic Analysis

Cell Reversible Potential is

Gibbs Energy For H2 + 1/2O2 -> H2O

Gibbs Energy For a Hydrogen Concentration Cell

Cathode Hydrogen Activity

Substitution Gives for a proton cell:

3

!

E ="#G

nF

!G = !G°(T ) + RT ln

ah2o

ah2 ao2

"

# $

%

& '

!G = RT lnah2"cathode

ah2"anode

#

$ %

&

' (

Ka =ah2o

ah2 ao2 cathode

!G = "RT ln Ka( )+ RT lnah2o"cathode

ah2"anode ao2"cathode

#

$ %

&

' (

Driving Force Comparison

High driving force even at high fuel utilization

4

Max. Efficiency Comparison Proton Cell

5

Oxygen Cell

Single Stage

Two Stage

BaCeO3 Proton Conductivity

Highest conductivity range from 0.01 to 0.016 in 700° to800°C range

~ half the oxygen ion conductivity of 8YSZ

6

Ionic Transference Number

BaCe0.8Y0.2O3-∂ measured using a concentrationcell

7

Comparison of Driving Force0.5 mm thick pellet of BCY (800°C)

Proton cell shows negligible change in drivingpotential compared to Oxygen cell

8

Observations OCV for P-SOFC is lower at 800°C, but approaches

O-SOFC at lower temp. Even with lower OCV, the Nernst potential crosses over

at utilization of >10% Absolute value of proton conductivity in BaCeO3 is lower

than the oxygen conductivity in YSZ– Generally electrode losses dominate cell performance

9

Instability of Perovskite

Stability of BaCeO3 in hydrocarbon based fuelis a major known issue

BaCeO3 + CO2 = BaCO3 + CeO2

BaCeO3 + H2O = Ba(OH)2 + CeO2

10

Reaction Product: CeO2

Traditional use for its high oxygen ionconductivity

Challenging as solid oxide fuel cellelectrolyte due to mixed conduction infuel atmosphere

11

Composite of BCY + YDC ??Composite of BCY + YDC ??

Enhanced Thermochemical StabilityCeramic Composite over BCY

12

• Stability in CO2+Air mixture (TGA)• BCY + YDC (crushed sintered disk)

Composite Stability in Syngas

13

• Stability in CO-CO2-H2-H2O mixture

BaCeO3 vs Composite Stability

Exposure to syngas at 900°C

14

Exposure to Syngas at 700°C

As low as 10 vol% Ceria showsimprovement in stability

15

Anode supported thin film cell

Dense thin film (~15 µm) BCY+YDC composite electrolyte

Anode: 50 wt% NiO and 50 wt% (BCY+YDC)

Cell before testing

Cell after testing Electrolyte surface

Anode supported P-SOFC

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.00.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

1.1

Voltage(V

)

Current Density (A/cm2)

Fuel flow rate: 35 sccm/min

Anode-support: Ni+(BCY+YDC)anode interlayer: Ni+(BCY+YDC)electrolyte: BCY+YDCcathode: LSCF

800oC (Fuel: H

2)

700oC (Fuel: H

2)

700oC (Fuel: Syngas, 77% H

2,15% CO, bal CO

2)

17

0.0 0.2 0.4 0.6 0.8 1.0 1.20.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8P

ow

er

De

nsity (

W/c

m2

)

Current Density (A/cm2)

Fuel flow rate: 35 sccm/min

Anode-support: Ni+(BCY+YDC)anode interlayer: Ni+(BCY+YDC)electrolyte: BCY+YDCcathode: LSCF

800oC (Fuel: H

2)

700oC (Fuel: H

2)

700oC (Fuel: Syngas, 77% H

2,15% CO, bal CO

2)

Anode supported P-SOFC

Stability in Syngas

19

• Fuel: Simulated high utilization (90%CO2 -balance humidified H2)

Conclusions

Proton SOFC shows high efficiency possibility Practical compositions requires operating

temperatures of 700°C or below to realize high tH Relatively lower proton conductivity requires thin,

supported electrolyte cells Proton Cells Can Effectively Use CO Via the

Water Gas Shift Reaction Chemical stability in syngas can be improved by

the composite approach

20

Work Supported by

DOE SBIR Grant: DE‑FG02‑06ER84595

DOE PMDr. Mani Manivannan

Dr. Joseph Stoffa

21