investigation of bscf cathode on gdc electrolyte for intermediate temperature sofcs

Investigation of BSCF Investigation of BSCF Cathode on GDC Electrolyte Cathode on GDC Electrolyte for Intermediate Temperature for Intermediate Temperature SOFCsSOFCs

Vann Brasher

Mentors: Dr. Daniel Mumm

Anh Duong

Sungrok Bang

The General OutlineThe General Outline

The SOFCSynthesis of SamplesTestingConclusion/Future Work

The SOFCThe SOFC

•Electrochemistry

½ O2 + 2 e- O2-

O2- + H2 H2O + 2 e-

•Conductivity Requirements

Electrolyte O-

Cathode/Anode e-

Solid State Ceramics

The SOFC

Fuel Cell Problems/Voltage Losses

Electrochemical Activation (Overpotential)

porosity

mixed conductivity Ohmic

thin layers/materials Mass Transport

gas flow system

The SOFCThe SOFC

•Purely Electronic Conducting Cathode (LSM)

•Triple Phase Boundary limitations

•Mixed Conduction (LSF, LSCF)

•Incompatible with YSZ!

Synthesis of SamplesSynthesis of Samples

GNP

Synthesis of SamplesSynthesis of Samples

B.5S.5CxF1-xO3-δ

X=.2,.5,.75 Pm3m cubic Red=Oxygen Green=A-site

Ba, Sr Blue=B-site

Co, Fe

Synthesis of Samples

Screen printing on isostatically pressed GDC

BSCF + binder 1cm2 symmetric

(both sides) calcine

+ fast, cheap

+ simulates industry

- inconsistant (ink, blades)

TestingTesting

X-Ray Diffraction Identification

XRD database

published XRD

Lattice parameter

Bragg’s Law Increase with Co Oxygen vacancy

XRD of BSCF major peak by molar cobalt content

0

500

1000

1500

2000

2500

31 31.5 32 32.5 33

2 theta (degrees)

Inte

nsi

ty (

CP

S)

0.2

0.5

0.75

TestingTesting

SEM imaging

Visual Characterization

Porosity Nano-Scale

Features Surface Area Uniformity

TestingTesting

Symmetric Cell Tests Impedance (10mV AC) from 350-550 °C DC voltage + Impedance from 600-750 °C V - iR = η

Impedance of BSCF 5528 at 500 C

-2.00E+00

0.00E+00

2.00E+00

4.00E+00

6.00E+00

8.00E+00

1.00E+01

1.20E+01

1.40E+01

0.00E+00 1.00E+01 2.00E+01 3.00E+01 4.00E+01 5.00E+01

Z real

-Z i

m

TestingTesting

BSCF5528

0.001

0.01

0.1

1

10

-0.05 0 0.05 0.1 0.15 0.2 0.25

Overpotential (V)

Cur

rent

(A/c

m2) 600C

650C

700C

750C

BSCF557525

0.001

0.01

0.1

1

10

-0.05 0 0.05 0.1 0.15 0.2 0.25

Overpotential (V)

Cur

rent

(A/c

m2) 600C

650C

700C

750C

ConclusionConclusion

Overpotential is a measure of losses due to electrochemical activity at the cathode.

BSCF557525 has lower overpotential better for applications in SOFC cathode.

Can be linked to lattice expansion. More oxygen vacancies, larger cations, etc.

Future WorkFuture Work

Screenprint with consistency and quality Achieve consistent Impedance data More samples, aim for repeatability Compare with other materials Analyze factors related to overpotential (i.e.

porosity, surface area) Full Cells?

Take it Away!Take it Away!

Fuel Cells are efficient & clean

Mixed Conductors make good Cathodes

Making & Testing Cells takes many steps!

Cobalt increases eletrochemical efficiency

Acknowledgements Acknowledgements

National Science Foundation

Dr. Mumm & Lab (Anh, Sungrok)

Said & UROP