Positive impact of the architecture of the oxygen electrode based on LNO and CGO for solid oxide electrochemical cells

Abstract

The Ruddlesden-Popper phase, strontium- and cobalt-free lanthanum nickelate, La₂NiO_4+δ (LNO), is a mixed-conducting oxide phase and a promising oxygen electrode for SOCs (solid oxide electrochemical cells), thanks to its high diffusion of oxygen and its surface exchange properties. The electrochemical performance is strongly related to the charge transfer at the triple phase boundaries in the surface path and the excorporation/incorporation reaction in the bulk path. In this context, this study explores a strategy to increase the number of active sites in LNO-based electrodes, by designing nanostructured active functional layers and incorporating gadolinium-doped ceria (CGO). Two architectural scenarios are proposed compared to a pure LNO reference: a uniform distribution of CGO in the volume of the LNO and a continuous compositional gradient, both fabricated for the first time by electrostatic spray deposition (ESD).

These designs are investigated based on phase structure, microstructure, elemental chemical composition, and electrochemical properties using SEM-EDS, XRD, and electrochemical impedance spectroscopy. Polarization resistance values are discussed as a function of the distribution of contact points in the electrode volume and LNO crystallization. The results suggest that the presented approach to achieve CGO: LNO-based gradient electrodes allows controlling the localization of the interfaces between the two phases, thereby optimizing charge transfer.