Towards Understanding Heterogeneous and Electrochemistry at La0.1Sr0.9TiO3-? SOFC Anodes

In the present contribution we combine modeling and experimental study of electrochemical hydrogen oxidation at an alternative perovskite type mixed-conducting SOFC anode. Composite electrodes on YSZ electrolytes (La0.1Sr0.9TiO3-?-Ce1-xGdxO2-? | YSZ) with different thicknesses and porosity were produced experimentally by screen printing-sintering and were characterized using symmetrical button-cells configuration. Electrochemical impedance spectra were recorded for H2/N2 atmosphere and temperature range 924 K - 1125 K at open circuit. The developed kinetic model incorporates elementary heterogeneous chemistry and electrochemical charge-transfer processes at two different electrochemical double layers (surface and interfacial), transport in the porous composite electrode (ionic and electronic conduction, multi-component porous diffusion and convection) as well as gas supply. Heterogeneous chemistry over LST electrode surface was evaluated based upon temperature programed desorption and reduction (TPD/TPR) measurements. The kinetics and thermodynamics of electrochemical charge-transfer processes were assessed by performing numerical impedance simulations over a whole range of operating conditions. This allows for a mechanistic interpretation of the origin of the three observed impedance features: (i) low frequency: transport in the gas supply (gas conversion) and/or hydrogen adsorption, (ii) intermediate frequency: charge transfer and surface double layer at the electrode/gas interface, (iii) high frequency: charge transfer and electrical double layer at the electrode/electrolyte interface.