Electrochemichal Characterization of Symmetrical Praseodymium Doped Ceria Electrodes for Solid Oxide Cells

Abstract

Decarbonizing industry at scale requires robust high-temperature electrolysers whose fuel electrodes avoid the long-term degradation modes of nickel-based cermets. This thesis evaluates symmetrical praseodymium-doped ceria (PDC) as a nickel-free mixed ionic–electronic conductor (MIEC) fuel electrode for solid oxide cells. Symmetrical Au/PDC10/GDC/8YSZ/GDC/PDC10 (gold/praseodymium-doped ceria 10%/gadolinium doped ceria/8% yttrium stabilized zirconia/gadolinium doped/praseodymium-doped ceria 10%/gold) ceria cells with two PDC thicknesses (~46 μm and ~19 μm) were prepared; their microstructure was examined by scanning electron microscopy (SEM) and electrochemical behavior probed by impedance spectroscopy under controlled H2/H2O mixtures and 750 – 900 °C conditions. Impedance spectra were decomposed using distribution-of-relaxation-times (DRT) analysis and equivalent-circuit modeling (ECM); Arrhenius and gas-partial-pressure studies yielded apparent activation energies and reaction orders. The thinner (~19 μm) electrode exhibited lower ohmic and polarization resistances and was selected for detailed analysis. Three reproducible processes were resolved: • a dominant low-frequency, H2-sensitive process consistent with hydrogen adsorption/dissociation. • a high-activation-energy, gas-insensitive process assigned to intrinsic electrode charge transfer; • and a low-activation-energy Gerischer-like contribution of unclear origin.

From these assignments, a hydrogen-controlled surface charge-transfer is identified as the rate-determining step under the studied conditions. By delivering well-defined quantitative kinetics and a correlation between relaxation times and physical steps, this work positions PDC10 as a promising Ni-free fuel electrode, along with providing guiding principles for improving activity and stability in the design of future electrodes.