of charge carriers Ragnar Strandbakke, Einar Vllestad, Truls Norby - - PowerPoint PPT Presentation

Ragnar Strandbakke, Einar Vøllestad, Truls Norby

Centre for Materials Science and Nanotechnology (SMN) FERMiO Oslo Innovation Centre

Characterization of double perovskite electrodes on ionic conductors with transport of more than one type

• f charge carriers

Truls Norby

BZCY: BaZr0.7Ce0.2Y0.1O3

Financial and scientific contributions from the EU ERANET RUS project «PROTON» and from the European Union's Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 621244 , Project «ELECTRA»

Einar Vøllestad

Double perovskite cathodes on BZCY electrolytes

 Some apparent electrode

polarisation resistances (in wet oxygen) from impedance spectroscopy

* Ragnar Strandbakke, Vladimir Cherepanov, Andrey Zuev, D. S. Tsvetkov, Christos Argirusis, Georgia Sourkouni-Argirusis, Stephan Prünte, Truls Norby, “Gd- and Pr-based double perovskite cobaltites as oxygen side electrodes for proton ceramic fuel cells and electrolyser cells”, under publication.

BaGd0.8La0.2Co2O6-δ Ba1-xGd0.8La0.2+xCo2O6-δ

0.8 1.0 1.2 1.4 1.6 1.8

• 2
• 1

1 2

X = 0.1 X = 0.5 X = 0* Log(Rp(cm2)) 1000 / T (K

• 1)

800 600 400

0.01 0.1 1 10 100

Rp(cm2) T (C) 0.04 cm

2

0.8 1.0 1.2 1.4 1.6 1.8

• 2
• 1

1 2

Rp,app(cm

2)

pO2: 1atm

log(Rp,app(cm

2))

1000/T (K-1)

800 600 400 0.01 0.1 1 10 100

T (C)

0.8 1.0 1.2 1.4 1.6 1.8

• 2
• 1

1 2

Rp,app(cm

2)

pO2: 1atm

log(Rp,app(cm

2))

1000/T (K-1)

800 600 400 0.01 0.1 1 10 100

T (C)

0.8 1.0 1.2 1.4 1.6 1.8

• 2
• 1

1 2

Rp,d,app Rp,ct,app

log(Rp(cm

2))

1000/T (K-1) pO2 = 1 atm

800 600 400 0.01 0.1 1 10 100

Rp(cm

2)

T (C)

O2- H+

Typical PCFC cathode Typical

• xide H+

conductor

PCFC oxygen electrodes (cathodes)

O2 4e- 2H2O 4H+ O2 4H+ 4e- 2H2O

Model PCFC cathode Ideal H+ conductor

2O2- 2O2- O2 4e- e- e-

Ideal PCFC cathode

O2 4H+ 4e- 2H2O 4H+

Ideal H+ conductor

PCFC oxygen electrodes (cathodes)

 Mixed conductivity: protons, oxide ions, electrons (holes)

Ragnar Strandbakke, Vladimir Cherepanov, Andrey Zuev, D. S. Tsvetkov, Christos Argirusis, Georgia Sourkouni-Argirusis, Stephan Prünte, Truls Norby, “Gd- and Pr-based double perovskite cobaltites as oxygen side electrodes for proton ceramic fuel cells and electrolyser cells”, under publication.

Typical PCFC cathode Typical

• xide H+

conductor

O2 4e- 2H2O 4H+ 2O2- 2O2- O2 4e- e- e-

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Impedance spectra yield apparent

electrode polarisation resistances

14.0 14.5 15.0 0.0

• 0.2
• 0.4
• 0.6
• 0.8
• 1.0
• 1.2

Rp2 Z//(cm2) Z

/(cm 2)

Rp1 S0 S1 S2

Electrolyte Electrode

Not enough information

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 …but a more correct treatment is required  needs more input parameters and assumptions

14.0 14.5 15.0 0.0

• 0.2
• 0.4
• 0.6
• 0.8
• 1.0
• 1.2

Rp2 Z//(cm2) Z

/(cm 2)

Rp1 S0 S1 S2

Electrolyte Electrode

Recipe: Get individual Rv’s from conductivity data Calibrate to Rv at S0

Rv at S0 is fitted to

  

   

2

, , , v

1 1 1 1

O v H v e v S

R R R R R

ln(1/RvT(Scm-1K))

 

            

      



RT H T d OH F z c F R

H mob H m O H H H H H v , ,

exp 1 / 1   

4 1 2 ,

exp 1 / 1

/ A,h h h e v

pO RT E T σ σ R         

 14.0 14.5 15.0 0.0

• 0.2
• 0.4

Rp2 Z  Z

/(cm 2)

Rp1 S0 S1 S2

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 …and now the charge transfer resistance:

14.0 14.5 15.0 0.0

• 0.2
• 0.4
• 0.6
• 0.8
• 1.0
• 1.2

Rp2 Z//(cm2) Z

/(cm 2)

Rp1 S0 S1 S2

Electrolyte Electrode

Recipe: Fix conductivity values at S0 Calculate properly Rv+Rp,1 at S1

Rv +Rp,ct,app at S1 is fitted to

    

      

2 2

, , , , , , , , , v 1

1 1 1 1

O ct p O v H ct p H v e v app ct p S

R R R R R R R R

       

 

RT E A O pH FpO R

A m n O H ct p

exp 1

2 2 / , ,

2

where

14.0 14.5 15.0 0.0

• 0.2
• 0.4

Rp2 Z  Z

/(cm 2)

Rp1 S0 S1 S2

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 …and the diffusion resistance

14.0 14.5 15.0 0.0

• 0.2
• 0.4
• 0.6
• 0.8
• 1.0
• 1.2

Rp2 Z//(cm2) Z

/(cm 2)

Rp1 S0 S1 S2

Electrolyte Electrode

Recipe: Fix conductivity + charge transfer valuesat S1 Calculate properly Rv+Rp,1+Rp,2 at S2

Rv + Rp,ct,app + Rp,d,app at S2 is fitted to

      

         

2 2 2

, , , , , , , , , , , , , , , 2

1 1 1 1

O d p O ct p O v H d p H ct p H v e v app d p app ct p v S

R R R R R R R R R R R

       

 

RT E A O pH FpO R

A m n O H d p

exp 1

2 2 / , ,

2

where

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Dependencies on

• Temperature
• pO2
• pH2O

give input to interpretation and modelling

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 2.0

Rp,app(cm2) EA: 1.25eV

pO2: 1atm pO2: 0.23 atm pO2: 0.05 atm pO2: 0.0029 atm

log(Rp,app(cm2)) 1000/T (K

• 1)

EA: 0.8eV EA: 0.5eV

700 600 500 400 0.1 1 10 100

T (C)

BaGd0.8La0.2Co2O6-δ

140 150 160 170 180

• 10
• 20
• 30
• 40

Z

/()

Z

//()

Dry Wet

T: 400°C

pO2: 1 atm

70 75 80 85 90 95 100

• 5
• 10
• 15
• 20
• 25
• 30

Dry Wet

Z

//()

Z/ ()

T: 650°C

pO2: 10-4 atm

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Modelling by fitting all data  Charge transfer vs diffusion  Effect of electronic conduction

1.0 1.2 1.4 1.6

• 2
• 1

1

Rp,ct,app Rp,d,app Rp,app

700 600 500 400 0.01 0.1 1 10

T (C) 1000/T (K

• 1)

log(R(cm2)) R(cm2)

1.0 1.2 1.4 1.6

• 2
• 1

1

Rp,ct Rp,d Rp Rp,app

700 600 500 400 0.01 0.1 1 10

T (C) 1000/T (K

• 1)

log(R(cm2)) R(cm2)

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Modelling by fitting all data  Protons vs oxide ions  Effect of electronic conduction

1.0 1.2 1.4 1.6

• 2
• 1

1 Rp,O

2-

Rp,H

+

Rp,d,H

+

Rp,ct,H

+

Rp Rp,app 700 600 500 400 0.01 0.1 1 10

T (C) 1000/T (K

• 1)

log(R(cm2)) R(cm2)

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Direct deconvolution of three rails  Protons vs oxide ions  Effect of electronic conduction

L1 Rv H+ RctH+ CPEctH+ RdH+ CPEdH+ Rv O2- RctO2- CPEctO2- RdO2- CPEdO2- Rv el CPEv

Ratio fixed

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Standard deconvolution

L1 Rv Cv Rct Rd CPEd CPEdl

15.70 15.75 15.80 15.85 15.90 15.95 16.00 16.05 16.10

• 0.3
• 0.2
• 0.1

0.0 0.1

Z

/ ()

Z

// ()

Data Standard deconvolution

Gives apparent Rp-values

T: 650 ⁰C Χ2: 9∙10-6

10

• 2

10

• 1

10 10

10

10

10

10

• 120
• 100
• 80
• 60
• 40
• 20

20 Z

Z

Error (%) Frequency

Ba0.9Gd0.8La0.3Co2O6-δ

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Direct deconvolution of three rails  Protons vs oxide ions  Effect of electronic conduction

15.70 15.75 15.80 15.85 15.90 15.95 16.00 16.05 16.10

• 0.3
• 0.2
• 0.1

0.0 0.1

Z

/ ()

Z

// ()

Data 3 rails deconvolution

L1 Rv H+ RctH+ CPEctH+ RdH+ CPEdH+ Rv O2- RctO2- CPEctO2- RdO2- CPEdO2- Rv el CPEv

Gives real Rp-values

Ratio fixed

T: 650 ⁰C Χ2: 7∙10-6

10

• 2

10

• 1

10 10

10

10

10

10

• 120
• 100
• 80
• 60
• 40
• 20

20 Error (%) Z

Z

Frequency

Ba0.9Gd0.8La0.3Co2O6-δ

Perovskite electrode on BaZr0.7Ce0.2Y0.1O3 (BZCY)

 Direct deconvolution of three rails  Protons vs oxide ions  Effect of electronic conduction

Standard deconvolution Approach II: 3 Rails

0.065 0.13 0.76 0.125 0.27 1.9 0.19 0.35 ) (

2 ct

cm R  ) (

2 d

cm R  ) (

2 p

cm R 

ct

R

d

R

p

R

) (

2 d 

O R ) (

d 

H R ) (

2 ct 

O R ) (

ct 

H R

Ba0.9Gd0.8La0.3Co2O6-δ

Conclusions

 Proton conducting oxides

• Exhibit also some oxide ion conduction

 especially at higher temperatures

• Exhibit some electronic conduction,

 especially at high or low pO2 (p- or n-type)  affecting especially electrode studies

 Oxide-based oxygen electrodes

• Tend to enhance oxide ion path over proton path

 Consequences for (oxygen) electrode studies

• Impedance spectra must be interpreted accordingly
• Conductivity data necessary as input
• Go to lower temperatures!
• Electrochemical impedances appear lower than they are