Durability of nanostructured LaPrNiO4+d electrode for solid oxide cells: Electrochemical, microstructural, and structural investigation

This work reports a durability study in galvanostatic mode at 700 °C for 900–960 h related to structural and microstructural evolution of LaPrNiO_4+δ (LPNO) oxygen electrode. The performances of the electrode, deposited by electrostatic spray deposition (ESD) and screen printing (SP), are not changed when operated under electrolysis current whereas a degradation is observed in fuel cell mode. Small quantities of secondary phases (La,Pr)₃Ni₂O_7-δ in the fine ESD microstructure and Pr₆O₁₁ on both ESD and SP layers are detected in the pristine electrode by synchrotron μ-X-ray diffraction and fluorescence. The destabilization of LPNO electrode, which slightly occurs in the ESD layer after thermal aging in air, is strongly accelerated under anodic and cathodic currents. Indeed, the formation of a new phase (La,Pr)₄Ni₃O_10-δ on both ESD and SP layers occurs with the extension of (La,Pr)₃Ni₂O_7-δ in the SP layer, and a significant increase in the amount Pr₆O₁₁ at high current density. Nevertheless, the electrode microstructure, determined by FIB-SEM tomography, remains stable under current whereas severe delamination is observed after aging in fuel cell mode. Based on these characterizations, the mechanisms of electrode aging have been discussed to explain the different behavior in fuel cell and electrolysis modes