Reaction Kinetics of Protons and Oxide Ions in LSM/Lanthanum Tungstate Cathodes with Pt Nanoparticle Activation

Abstract

Composite electrodes of La 0.8 Sr 0.2 MnO 3 (LSM) / La 28-x W 4+x O 54+3x/2 (x=0.85, "LWO56") on LWO56 electrolytes have been characterized by use of electrochemical impedance spectroscopy vs pO 2 and temperature from 900 ⁰C, where LWO56 is mainly oxide ion conducting, to 450 ⁰C, where it is proton conducting in wet atmospheres. The impedance data are analyzed in a model which takes into account the simultaneous flow of oxide ions and protons across electrolyte and electrodes, allowing extraction of activation energies and pre-exponential factors for the partial electrode reactions of protons and oxide ions. One composite electrode was infiltrated with Pt nanoparticles with average diameter of 5 nm, lowering the overall electrode polarization resistance (R p ) at 650 ⁰C from 260 to 40 Ω cm 2 . The Pt-infiltrated electrode appears to be rate limited by surface reactions with activation energy of ~90 kJ mol -1 in the low temperature proton 2 transport regime and ~150 kJ mol -1 in the high temperature oxide ion transport regime. The charge transfer reaction, which makes a minor contribution to R p , exhibits activation energies of ~85 kJ mol -1 for both oxide ion and proton charge transfer.

Electrochemical performance of Co3O4/CeO2 electrodes in H2S/H2O atmospheres in a proton-conducting ceramic symmetrical cell with BaZr0.7Ce0.2Y0.1O3 solid electrolyte

“…It should be again mentioned that the duration of each temperature step was equal to 3 h and impedance spectra were acquired every 30 min. Again, the dominant feature in the impedance spectra ( Figure 4 The charge transfer contribution compared to mass transfer processes is lowered at 850 o C, which could be attributed to the red-ox processes of intermediate reaction products (e.g., sulphur-containing species) or to the partial O 2transport of BZCY72 at high temperatures, as it has been observed in previous relevant works [18,19]. For this reason, the activation energy for Rct (29.7 kJ/mol) has been calculated taking into account the corresponding values in the temperature range of 700 -800 o C, thus excluding the point at 850 o C. (Fig.…”

Effect of Cation Ordering on the Performance and Chemical Stability of Layered Double Perovskite Cathodes

“…Adler et al [43] published a detailed study on the electrode kinetics of porous mixed-conducting oxygen electrodes based on oxide-ion conducting electrolyte, using a continuum modeling to analyze the oxygen reduction reaction. Furthermore, Strandbakke et al [44] showed that pre-exponential values of the Arrhenius plot are indicative of the microstructure impact in the electrochemical performance. A similar microstructure for both LaBaCo 2 O 5+δ and La 0.5 Ba 0.5 CoO 3−δ materials can be seen in Figure S1 and can also be confirmed with the similar pre-exponential values calculated from Figure 9 (13.55 for La 0.5 Ba 0.5 CoO 3−δ and 14.75 for LaBaCo 2 O 5+δ ).…”

High-Performance La0.5Ba0.5Co1/3Mn1/3Fe1/3O3−δ-BaZr1−zYzO3−δ Cathode Composites via an Exsolution Mechanism for Protonic Ceramic Fuel Cells

“…In an effort to lower the Co-content due to its high cost, the development of cathodes consisting of a mixture of 3d transition metals is investigated. Well-studied cathodes with Fe, Mn, or mixtures with Co have been reported in both single materials and composites [10,18,19]. Y-doped barium zirconate materials exhibit fast proton conduction and are state-of-the art electrolytes in PCFCs [1,20,21].…”