Abstract
The objective of this study is to locate new selective electrode materials for the reduction of NO, and to gain a better understanding of the processes involved in reduction and oxidation of NO. A variety of electrodes based on mixed conducting perovskites and oxide ion conducting electrolytes of doped ceria (CeO{sub 2}) was tested as electrode materials. Symmetrical cells and three electrode cells with composite electrodes of (La{sub 1-x}Sr{sub x}){sub s}- MnO{sub 3} (LSM) (x=0.15, 0.5 and s = 0.9, 0.99), La{sub 1-y} Sr{sub y}Co{sub 1-z}Fe{sub z}O{sub 3} (y = 0.25, 0.4 and z = 1 (LSF), 0.8 (LSCF)) and ceria doped with Gd or Pr were prepared. Using three electrode cells with composite electrodes it was possible to observe NO reduction at 600 deg. C when the electrodes were polarised to -0.6 V vs Pt/air or lower. The electrode with LSM15 and Ce{sub 0.9}Gd{sub 0.1}O{sub 2} (CGO10) had the highest activity, while the LSM50 and Ce{sub 0.8}Pr{sub 0.2}O{sub 2} (CPO20) electrode had the highest current efficiency (CE). Cyclic voltammetry measurements showed that the LSM50/CPO20 had the best selectivity for NO in the temperature range 300 to 400 deg. C. Technological investigations were performed using porous cell stacks with 13
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Citation Formats
Larsen Werchmeister, R M.
NO conversion electrocatalysts.
Denmark: N. p.,
2010.
Web.
Larsen Werchmeister, R M.
NO conversion electrocatalysts.
Denmark.
Larsen Werchmeister, R M.
2010.
"NO conversion electrocatalysts."
Denmark.
@misc{etde_1011551,
title = {NO conversion electrocatalysts}
author = {Larsen Werchmeister, R M}
abstractNote = {The objective of this study is to locate new selective electrode materials for the reduction of NO, and to gain a better understanding of the processes involved in reduction and oxidation of NO. A variety of electrodes based on mixed conducting perovskites and oxide ion conducting electrolytes of doped ceria (CeO{sub 2}) was tested as electrode materials. Symmetrical cells and three electrode cells with composite electrodes of (La{sub 1-x}Sr{sub x}){sub s}- MnO{sub 3} (LSM) (x=0.15, 0.5 and s = 0.9, 0.99), La{sub 1-y} Sr{sub y}Co{sub 1-z}Fe{sub z}O{sub 3} (y = 0.25, 0.4 and z = 1 (LSF), 0.8 (LSCF)) and ceria doped with Gd or Pr were prepared. Using three electrode cells with composite electrodes it was possible to observe NO reduction at 600 deg. C when the electrodes were polarised to -0.6 V vs Pt/air or lower. The electrode with LSM15 and Ce{sub 0.9}Gd{sub 0.1}O{sub 2} (CGO10) had the highest activity, while the LSM50 and Ce{sub 0.8}Pr{sub 0.2}O{sub 2} (CPO20) electrode had the highest current efficiency (CE). Cyclic voltammetry measurements showed that the LSM50/CPO20 had the best selectivity for NO in the temperature range 300 to 400 deg. C. Technological investigations were performed using porous cell stacks with 13 layers (= 6 cells) made from laminated tapes of electrolyte (CGO10) and LSM and doped ceria based composite electrodes. The electrodes were infiltrated with pure ceria, CGO10 or CPO20. Gas conversion was observed when the cell stack was polarised with 4.5 V. The infiltration with pure ceria gave the highest activity, while the highest CE was seen for infiltration with CGO10. NO conversion could be detected at temperatures as low as 250 deg. C for the best cell stack. For each infiltration approximately 8 mg/cm2 ceria was infiltrated, and multiple infiltrations increased the activity. The cell stacks with LSM50/CPO10 electrodes had the highest activity, while the LSM15/CGO10 electrodes had the highest CE. Thus the results did not correspond well with the measurements on three electrode cells and symmetrical cells, apparently the infiltration changed the surface chemistry of the electrodes. N{sub 2} and O{sub 2} was formed in stoichiometric amounts at polarisation at 400 deg. C, but at lower temperatures too small amounts were formed, especially O{sub 2}, indicating formation NO{sub 2} instead of reduction of NO. The symmetrical cells were characterised with electrochemical impedance spectroscopy (EIS). Generally the electrodes had higher polarisation resistance (R{sub p}) in an NO containing atmosphere than in air at high temperature (600 deg. C), while at lower temperature (300 to 400 deg. C) the R{sub p} was largest for electrodes in air, i.e. the activation energy being lower for electrodes in 1 % NO in Ar than in air. For the series of electrodes with LSM, the electrodes with LSM50/CPO20 had the lowest R{sub p} values, but still all the electrodes based on LSF and LSCF were better oxygen electrodes, especially at 600 deg. C. The impedance spectra of electrodes in NO at open circuit voltage (OCV) were dominated by a large low frequency arc, especially at high temperatures. This arc was a type of conversion arc. The arc appeared because the electrodes did not react directly electrochemically with NO around OCV, but with an intermediate (likely NO{sub 2}) present in low concentration. This intermediate was formed catalytically by the electrodes. EIS measurements of the polarised three electrode cells showed that the kinetics in NO containing atmosphere changes at polarisation of -0.6 V vs air/Pt or lower. (Author)}
place = {Denmark}
year = {2010}
month = {Feb}
}
title = {NO conversion electrocatalysts}
author = {Larsen Werchmeister, R M}
abstractNote = {The objective of this study is to locate new selective electrode materials for the reduction of NO, and to gain a better understanding of the processes involved in reduction and oxidation of NO. A variety of electrodes based on mixed conducting perovskites and oxide ion conducting electrolytes of doped ceria (CeO{sub 2}) was tested as electrode materials. Symmetrical cells and three electrode cells with composite electrodes of (La{sub 1-x}Sr{sub x}){sub s}- MnO{sub 3} (LSM) (x=0.15, 0.5 and s = 0.9, 0.99), La{sub 1-y} Sr{sub y}Co{sub 1-z}Fe{sub z}O{sub 3} (y = 0.25, 0.4 and z = 1 (LSF), 0.8 (LSCF)) and ceria doped with Gd or Pr were prepared. Using three electrode cells with composite electrodes it was possible to observe NO reduction at 600 deg. C when the electrodes were polarised to -0.6 V vs Pt/air or lower. The electrode with LSM15 and Ce{sub 0.9}Gd{sub 0.1}O{sub 2} (CGO10) had the highest activity, while the LSM50 and Ce{sub 0.8}Pr{sub 0.2}O{sub 2} (CPO20) electrode had the highest current efficiency (CE). Cyclic voltammetry measurements showed that the LSM50/CPO20 had the best selectivity for NO in the temperature range 300 to 400 deg. C. Technological investigations were performed using porous cell stacks with 13 layers (= 6 cells) made from laminated tapes of electrolyte (CGO10) and LSM and doped ceria based composite electrodes. The electrodes were infiltrated with pure ceria, CGO10 or CPO20. Gas conversion was observed when the cell stack was polarised with 4.5 V. The infiltration with pure ceria gave the highest activity, while the highest CE was seen for infiltration with CGO10. NO conversion could be detected at temperatures as low as 250 deg. C for the best cell stack. For each infiltration approximately 8 mg/cm2 ceria was infiltrated, and multiple infiltrations increased the activity. The cell stacks with LSM50/CPO10 electrodes had the highest activity, while the LSM15/CGO10 electrodes had the highest CE. Thus the results did not correspond well with the measurements on three electrode cells and symmetrical cells, apparently the infiltration changed the surface chemistry of the electrodes. N{sub 2} and O{sub 2} was formed in stoichiometric amounts at polarisation at 400 deg. C, but at lower temperatures too small amounts were formed, especially O{sub 2}, indicating formation NO{sub 2} instead of reduction of NO. The symmetrical cells were characterised with electrochemical impedance spectroscopy (EIS). Generally the electrodes had higher polarisation resistance (R{sub p}) in an NO containing atmosphere than in air at high temperature (600 deg. C), while at lower temperature (300 to 400 deg. C) the R{sub p} was largest for electrodes in air, i.e. the activation energy being lower for electrodes in 1 % NO in Ar than in air. For the series of electrodes with LSM, the electrodes with LSM50/CPO20 had the lowest R{sub p} values, but still all the electrodes based on LSF and LSCF were better oxygen electrodes, especially at 600 deg. C. The impedance spectra of electrodes in NO at open circuit voltage (OCV) were dominated by a large low frequency arc, especially at high temperatures. This arc was a type of conversion arc. The arc appeared because the electrodes did not react directly electrochemically with NO around OCV, but with an intermediate (likely NO{sub 2}) present in low concentration. This intermediate was formed catalytically by the electrodes. EIS measurements of the polarised three electrode cells showed that the kinetics in NO containing atmosphere changes at polarisation of -0.6 V vs air/Pt or lower. (Author)}
place = {Denmark}
year = {2010}
month = {Feb}
}