Characterization of double perovskite electrodes on ionic conductors with transport of more than one type of charge carriers Ragnar Strandbakke, Einar Vøllestad, Truls Norby Truls Norby Einar Vøllestad BZCY: BaZr 0.7 Ce 0.2 Y 0.1 O 3 Centre for Materials Science and Nanotechnology (SMN) FERMiO Oslo Innovation Centre 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»
Double perovskite cathodes on BZCY electrolytes T ( C) T ( C) T ( C) T ( C) 800 800 800 600 600 600 400 400 400 800 600 400 2 2 2 100 100 100 2 100 Some apparent electrode p O 2 = 1 atm p O 2 : 1atm p O 2 : 1atm H + polarisation resistances (in 1 1 1 10 10 10 1 10 wet oxygen) from impedance spectroscopy 2 )) 2 )) Log(R p ( cm 2 )) 2 )) log( R p,app ( cm log( R p,app ( cm R p ( cm 2 ) log( R p ( cm 2 ) 0 0 1 1 2 ) 0 0 1 1 R p,app ( cm R p,app ( cm 2 ) R p ( cm Ba 1-x Gd 0.8 La 0.2+x Co 2 O 6- δ BaGd 0.8 La 0.2 Co 2 O 6- δ X = 0.1 -1 -1 -1 -1 O 2- 0.1 0.1 0.1 0.1 X = 0.5 X = 0* R p,d,app 0.04 cm 2 R p ,ct,app * Ragnar Strandbakke, Vladimir Cherepanov, Andrey -2 -2 -2 0.01 0.01 0.01 -2 0.01 Zuev, D. S. Tsvetkov, Christos Argirusis, Georgia Sourkouni-Argirusis, Stephan Prünte, Truls Norby, “ Gd- and Pr-based double perovskite cobaltites as oxygen 0.8 0.8 1.0 1.0 1.2 1.2 1.4 1.4 1.6 1.6 1.8 1.8 side electrodes for proton ceramic fuel cells and 0.8 1.0 1.2 1.4 1.6 1.8 0.8 1.0 1.2 1.4 1.6 1.8 electrolyser cells” , under publication. 1000/T (K -1 ) 1000/T (K -1 ) 1000/T (K -1 ) -1 ) 1000 / T (K
PCFC oxygen electrodes (cathodes) Typical Ideal H + Ideal H + Ideal Model Typical PCFC PCFC oxide H + conductor PCFC conductor cathode cathode cathode conductor e - e - 4e - 4e - 2O 2- 2O 2- O 2 4e - 4H + 4H + 4e - O 2 O 2 4H + 4H + O 2 2H 2 O 2H 2 O 2H 2 O
PCFC oxygen electrodes (cathodes) Mixed conductivity: protons, oxide ions, electrons (holes) Typical Typical PCFC oxide H + cathode conductor e - e - 4e - 2O 2- 2O 2- O 2 4e - 4H + O 2 Ragnar Strandbakke, Vladimir Cherepanov, Andrey Zuev, D. S. Tsvetkov, 2H 2 O 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.
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Impedance spectra yield apparent -1.2 electrode polarisation resistances -1.0 -0.8 Z // ( cm 2 ) Electrolyte Electrode -0.6 -0.4 S1 S2 S0 R p 2 R p 1 -0.2 0.0 14.0 14.5 15.0 / ( cm 2 ) Z Not enough information
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) …but a more correct treatment is required -1.2 needs more input parameters and assumptions -1.0 -0.8 Z // ( cm 2 ) Electrolyte Electrode -0.6 -0.4 S1 S2 S0 R p 2 R p 1 -0.2 0.0 14.0 14.5 15.0 / ( cm 2 ) Z Recipe: Get individual R v ’s from conductivity data Calibrate to R v at S0
1 R v at S0 is fitted to R R S 0 v 1 1 1 R R R 2 v , e v , H v , O H 1 mob , H 0 1 / R F c z F OH d exp O m v , H H H H H H T RT E 1 σ σ 0 A,h 1 / 4 1 / R exp pO h h 2 v , e T RT Z -0.4 ln(1/ R v T(Scm- 1 K)) S1 S2 S0 R p 1 R p 2 -0.2 0.0 14.0 14.5 15.0 / ( cm 2 ) Z
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) …and now the charge transfer resistance: -1.2 -1.0 -0.8 Z // ( cm 2 ) Electrolyte Electrode -0.6 -0.4 S1 S2 S0 R p 2 R p 1 -0.2 0.0 14.0 14.5 15.0 / ( cm 2 ) Z Recipe: Fix conductivity values at S0 Calculate properly R v +R p,1 at S1
R v +Rp,ct,app at S1 is fitted to Z -0.4 S1 1 S2 S0 R p 1 R p 2 R R R -0.2 S 1 v p , ct , app 1 1 1 0.0 14.0 14.5 15.0 R R R R R 2 2 / ( cm 2 ) v , e v , H p , ct , H v , O p , ct , O Z where 1 E n m 0 A FpO pH O A exp 2 2 R RT 2 p , ct , H / O
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) …and the diffusion resistance -1.2 -1.0 -0.8 Z // ( cm 2 ) Electrolyte Electrode -0.6 -0.4 S1 S2 S0 R p 2 R p 1 -0.2 0.0 14.0 14.5 15.0 / ( cm 2 ) Z Recipe: Fix conductivity + charge transfer valuesat S1 Calculate properly R v +R p,1 +R p,2 at S2
R v + R p,ct,app + R p,d,app at S2 is fitted to 1 R R R R S 2 v p , ct , app p , d , app 1 1 1 R R R R R R R 2 2 2 v , e v , H p , ct , H p , d , H v , O p , ct , O p , d , O where 1 E n m 0 A FpO pH O A exp 2 2 R RT 2 p , d , H / O
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) T ( C) Dependencies on 700 600 500 400 2.0 100 -30 ◦ Temperature p O 2 : 1atm Dry Dry -40 Wet p O 2 : 0.23 atm ◦ -25 Wet p O 2 T: 400°C T: 650°C 1.5 p O 2 : 0.05 atm ◦ pH 2 O p O 2 : 0.0029 atm -20 -30 p O 2 : 1 atm p O 2 : 10 -4 atm give input to // ( ) 1.0 10 // ( ) -15 Z -20 interpretation and Z E A : 0.8eV -10 modelling 0.5 log( R p,app ( cm 2 )) E A : 0.5eV -10 R p,app ( cm 2 ) -5 0.0 1 0 0 140 70 75 150 80 160 85 170 90 95 180 100 Z / ( ) / ( ) Z -0.5 -1.0 0.1 E A : 1.25eV BaGd 0.8 La 0.2 Co 2 O 6- δ -1.5 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 -1 ) 1000/T (K
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Modelling by fitting all data Charge transfer vs diffusion Effect of electronic conduction T ( C) T ( C) 700 700 600 600 500 500 400 400 1 1 10 10 R p,app R p 0 0 1 1 log( R ( cm 2 )) log( R ( cm 2 )) R p,ct R ( cm 2 ) R ( cm 2 ) R p,ct,app R p,app -1 -1 0.1 0.1 R p,d,app R p,d -2 -2 0.01 0.01 1.0 1.0 1.2 1.2 1.4 1.4 1.6 1.6 -1 ) -1 ) 1000/T (K 1000/T (K
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Modelling by fitting all data Protons vs oxide ions Effect of electronic conduction T ( C) 700 600 500 400 1 10 0 1 log( R ( cm 2 )) R ( cm 2 ) R p ,O 2- R p,H -1 + 0.1 R p,d,H + R p,ct,H + R p R p,app -2 0.01 1.0 1.2 1.4 1.6 -1 ) 1000/T (K
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Direct deconvolution of three rails Protons vs oxide ions Effect of electronic conduction Ratio fixed L1 Rv H+ RctH+ RdH+ CPEctH+ CPEdH+ Rv O2- RctO2- RdO2- CPEctO2- CPEdO2- Rv el CPEv
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Standard deconvolution Ba 0.9 Gd 0.8 La 0.3 Co 2 O 6- δ 0.1 Gives apparent R p -values 0.0 Data / ( ) Standard deconvolution -0.1 Z 20 0 -20 T: 650 ⁰ C Error (%) -40 -0.2 -60 Χ 2 : 9∙10 -6 L1 Rv Rct Rd -80 // Z -100 / Z Cv CPEd -120 -2 -1 0 1 2 3 4 5 10 10 10 10 10 10 10 10 Frequency CPEdl -0.3 15.70 15.75 15.80 15.85 15.90 15.95 16.00 16.05 16.10 // ( ) Z
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Direct deconvolution of three rails Ba 0.9 Gd 0.8 La 0.3 Co 2 O 6- δ Protons vs oxide ions Effect of electronic conduction 0.1 Gives real R p -values 0.0 Ratio fixed Data / ( ) 3 rails deconvolution -0.1 Z L1 Rv H+ RctH+ RdH+ 20 0 -20 CPEctH+ CPEdH+ T: 650 ⁰ C Error (%) -40 -0.2 -60 Χ 2 : 7∙10 -6 Rv O2- RctO2- RdO2- -80 // Z -100 / Z CPEctO2- CPEdO2- -120 -2 -1 0 1 2 3 4 5 10 10 10 10 10 10 10 10 Frequency -0.3 Rv el 15.70 15.75 15.80 15.85 15.90 15.95 16.00 16.05 16.10 // ( ) Z CPEv
Perovskite electrode on BaZr 0.7 Ce 0.2 Y 0.1 O 3 (BZCY) Direct deconvolution of three rails Ba 0.9 Gd 0.8 La 0.3 Co 2 O 6- δ Protons vs oxide ions Effect of electronic conduction Standard deconvolution Approach II: 3 Rails 0.13 R ( H ) 2 ct 0.065 R R ( cm ) ct ct 0.76 2 R ( O ) ct 0.27 R ( H ) R 2 d ( cm ) 0.125 R d 1.9 d 2 R ( O ) d R 2 0.19 0.35 ( cm ) R p p
Conclusions Proton conducting oxides ◦ Exhibit also some oxide ion conduction especially at higher temperatures ◦ Exhibit some electronic conduction, especially at high or low p O 2 (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
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