Overstoichiometric oxides Ln2NiO4+δ (Ln = La, Pr or Nd) as oxygen anodic electrodes for solid oxide electrolysis application
Résumé
Improving the oxygen electrode performances of the single solid oxide electrolysis cell (SOEC) is of peculiar interest as it contributes to a large extent to the cell polarization resistance. The present study focuses on alternative oxygen electrode materials: the oxygen overstoichiometric rare-earth nickelate oxides Ln2NiO4+δ (Ln = La, Pr or Nd). Their electrochemical properties are measured on three-electrode symmetrical half-cells under zero dc conditions and under anodic polarization. The electrochemical characteristics are compared to those of the usual perovskite La0.6Sr0.4Fe0.8Co0.2O3-δ (LSFC) electrode. Under polarization, in the temperature range from 600 °C to 800 °C, the Pr2NiO4+δ-based cells exhibit the highest performances. At the same anodic overpotential of 0.15 V/Pt/air, the current densities measured through Pr2NiO4+δ nickelate-based cells are more than ten times larger than those obtained with a cell based on LSCF. The modeling of the anodic overpotential phenomena (activation and concentration terms) occurring at the oxygen electrode is achieved and discussed.