July 29, 2010

Exposure Limits of Higher

Hydrocarbons for SOFCSECA 2010 Workshop

NETL Fuel Cell Group

July 29, 2010

Kirk Gerdes

Research Group Leader, Fuel Cells

NETL Morgantown

2

Overview

• NETL FC Group Background

• Discussion of Coal Syngas Exposure Results

– Individual contaminants testing protocol

• Mercury

• Naphthalene, Benzene

• PEG/DME

• Conclusions

• FY11 planned research

3

NETL Fuel Cells Group

• Federal activity

– 5 federal research projects

• Anode contaminates and liquid metal anode

• Cathode infiltration

• Hybrid gas turbine / FC operation and controls

• GC-ICP/MS

– 4 federal researchers and 5 post-doctoral research associates

• University activity

– 5 university research projects (CMU and WVU)

• Cathode crystallographic evolution

• Cathode infiltration and microstructural modeling (2 projects)

• Fundamentals of oxygen reduction reaction (ORR)

• Hybrid controls

• Contract labor support

– Research management and support activities

4

Contaminants - Problem Outline

• Analyze the interaction of trace materials in direct syngas with the

solid oxide fuel cell (SOFC) anode

• Thermodynamic analysis

– Elements present

• As, Cd, Hg, Pb, Sb, Se

– Elements interacting

• As, Sb

• Stable secondary phases

• Laboratory results

– As, P, S, Se

0.00

0.03

0.06

0.09

0.12

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01

Extrapolated range Tested range

hrs

days

mos

yrs

decs

Acceptable degradation

Zero-effect

Trace Material ConcentrationD

egra

dat

ion

[%

lo

ss p

er 1

00

0 h

ou

rs]

0.00

0.03

0.06

0.09

0.12

1.E-05 1.E-04 1.E-03 1.E-02 1.E-01 1.E+00 1.E+01

Extrapolated range Tested rangeExtrapolated range Tested range

hrs

days

mos

yrs

decs

Acceptable degradation

Zero-effect

Trace Material ConcentrationD

egra

dat

ion

[%

lo

ss p

er 1

00

0 h

ou

rs]

A. Martinez, K. Gerdes, R. Gemmen, and J. Poston, Journal of Power Sources, 195, (2010) p5206–12.

• Additionally interested in higher hydrocarbons and process

materials (benzene, naphthalene, ethylene, Selexol)

5

Contaminants - Background

• Trace material can attack the anode by any (or all) of three

primary degradation mechanism classes

• Class I – Physical blocking of fuel feed pores

• Carbon whiskers (graphite), incombustible materials (Si)

• Class II – Surface adsorption

• Deactivation of catalytic sites (S, Se)

• Class III – Chemical reaction

– Class IIIA – Formation of secondary metal phases (P, As, Sb)

– Class IIIB – Formation of metal solutions (C)

J. Hansen, “Correlating Sulfur Poisoning of SOFC Nickel Anodes by a Temkin Isotherm”

Electrochem. Solid-State Lett., Volume 11, Issue 10, pp. B178-B180 (2008)

6

HHC Contaminants - Background

• Standard cell is purchased commercially

– Ni/YSZ anode; YSZ electrolyte; LSM cathode

• Cell is exposed to precisely controlled mass of trace material

– Benzene @ 15 and 150 ppm

– Naphthalene @ 100 and 500 ppm

– PEG/DME @ 1 and 3.5 ppm

– Mercury @ 1 and 10 ppm* Exposure significantly exceeds

gasifier effluent concentration

• Electrochemical reaction

monitored

– Temporal voltage, EIS

• Post-operational microscopy

– SEM/EBSD, XPS, TEM M.F. Singleton and P. Nash

7

HHC Contaminants - Background

• Standard cell is purchased commercially

– Ni/YSZ anode; YSZ electrolyte; LSM cathode

• Cell is exposed to precisely controlled mass of trace material

– Benzene @ 15 and 150 ppm

– Naphthalene @ 100 and 500 ppm

– PEG/DME @ 1 and 3.5 ppm

– Mercury @ 1 and 10 ppm* Exposure significantly exceeds

gasifier effluent concentration

• Electrochemical reaction

monitored

– Temporal voltage, EIS

• Post-operational microscopy

– SEM/EBSD, XPS, TEM M.F. Singleton and P. Nash

8

Test Parameters

• Cathode – Air @ 1000 mL/min

• Anode:

– Hydrogen: 87.3 mL/min (29.1%)

– Carbon monoxide: 85.8 mL/min (28.6%)

– H2O: 81.8 mL/min (27.3%)

– Carbon dioxide: 36.0 mL/min (12.0%)

– Nitrogen: 9.6 mL/min (3.2%)

• Temperature - 800 C

• Operating condition – 250 mA/cm2

9

V = 0.831e-8e-6t

R² = 0.4698

0.600

0.650

0.700

0.750

0.800

0.850

0.900

0.950

1.000

0 100 200 300 400 500

Po

ten

tia

l [V

]

Exposure Time [h]

1 ppm Mercury

10 ppm Mercury

Degradation Rate = 1.4% / 1000 h

1 ppm Mercury

10 ppm Mercury

Degradation Rate = 1.4% / 1000 h

R² = 0.8151

Mercury Data (1 ppm data/equation shown)

Mercury Overpotential

10

SEM - Mercury

Mercury Exposure (1 ppm)

11

Naphthalene Data (500 ppm data/equation shown)

Naphthalene overpotential

12

0.00

0.04

0.08

0.12

0.16

0.20

0.00 0.10 0.20 0.30 0.40 0.50

-Im

ag

inary

Im

ped

an

ce

[W*cm

2]

Real Impedance [W*cm2]

Clean Syngas100 Hours200 Hours325 Hours425 Hours500 Hours

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

200

79.6

Hz

159

Hz

100

Hz

Naphthalene Impedance - 500 ppm

Naphthalene impedance

13

SEM – Naphthalene

Naphthalene SEM Image - 500 ppm

14

XPS - Naphthalene

• Naphthalene exposed samples showed minimal carbon

0.00

200.00

400.00

600.00

800.00

1000.00

1200.00

1400.00

1600.00

1800.00

270.00275.00280.00285.00290.00295.00300.00

Inte

nsi

ty (

arb

ritr

ary

Un

its)

Binding Energy (eV)

100 ppm

Naphthalene

H2 Treated Cell

500 ppm

Naphthalene

15

TEM imaging – Naphthalene

• Five elements within inclusion: Ni, Al, Si, C, and O

• Titan 80-300 (aberration

corrected HR-STEM)

• Accelerating V=300 kV

• Resolution = 0.07 nm

• The beam size is substantially

smaller than the particle (<1

nm)

Al Ni C Si O

10nm

16

TEM/EDS – Naphthalene

• JEOL 2100F Cs-Corrected STEM (U Michigan, a system which is comparable to Titan system)

• C distributes evenly in the Ni grain.

• Result is consistent with Titan data.

• C observed everywhere through the 500 ppm sample.

• Sample is cleaned using ion-mill but C remains.

• New sample prepared and similar result acheived.

• Preliminary confirmation that C is major solid solution specie.

Image Carbon map

17

Benzene Data (150 ppm data/equation shown)

Benzene overpotential

18

0.00

0.01

0.02

0.03

0.04

0.00 0.05 0.10 0.15 0.20

-Im

ag

inary

Im

ped

an

ce

[W

]

Polarization Resistance [W]

0 h

267 h

384 h

504 h

100 Hz

79.6

Hz63.2

Hz

63.2

Hz

Benzene Impedance - 15 ppm

Benzene impedance

19

PEG/DME data (1 ppm (g) data/equation shown)

3.5 ppm data inconclusive due to noise

PEG/DME Overpotential

20

Discussion – Analysis Method

V0

VX%

VF

t0 tFtX%

Baseline Cell +

Contaminant

Baseline Cell

• Empirical degradation model assumptions

– Initial degradation is well modeled by exponential decay

– Long term (2000 + hours) cell degradation is linear

21

Exposure limit - Naphthalene

• First order with respect to concentration in range of 100-500 ppm

• Exposure limit depends on

– Assumed baseline cell degradation rate (1%, 0.5%, 0.25% / 1000 hours)

– Acceptable final operating voltage

0.25% / 1000 h0.50% / 1000 h1.0% / 1000 h

22

Exposure limit - Benzene

• Zero order with respect to concentration in range of 15-150 ppm

– Degradation rate too similar b/n two concentrations to extrapolate limit

0.25% / 1000 h0.50% / 1000 h1.0% / 1000 h

23

Conclusions

• Naphthalene

– SOFC exposed to naphthalene at 150 and 500 ppm demonstrated

obvious performance degradation

• Rates greater than those for benzene.

– After 40,000 h, the SOFC will produce usable potential of :

• 0.7 V at 110 ppm @ base cell degr rate of 0.25% per 1000 h.

• 0.6 V at 1200 ppm @ base cell degr rate of 0.25% per 1000 h.

• 0.6 V at 360 ppm @ base cell degr rate of 0.50% per 1000 h

24

Conclusions

• Mercury

– SOFC exposed to mercury at 1 and 10 ppm shows no

performance degradation

– Results agree with thermodynamic analyses and literature

– Mercury cleanup is not required for fuel cell

• Benzene

– SOFC exposed to benzene at 15 and 150 ppm showed

noticeable performance degradation.

– Cleanup to less than 150 ppm is recommended

25

Continued HHC Exposure testing

• Complete tests on PGE/DME (3.5 ppm repeat)

• Initiate Ethylene tests at 100-1000 ppm

– Predict exposure limitations

• Carefully monitor grain growth

– Record sufficient microstructure observations to ensure

statistical relevance

• Spot check literature results for H2Se and AsH4

26

Acknowledgements

• Principal Investigator

Gregory Hackett (NETL)

• Microscopy

Yun Chen (WVU), Xueyan Song (WVU), Jim Poston

(NETL)

• Discussion

Harry Finklea (WVU), Xingbo Liu (WVU), John Zondlo

(WVU), Harry Abernathy (NETL)

• SECA