Influence of Sr Doping on Surface Chemistry and Electrochemical Performance of LaMnO 3 -Based Solid Oxide Cell Oxygen Electrodes

Partial substitution of La 3+ by Sr 2+ in LaMO 3 -type perovskite solid oxide cell (SOC) oxygen electrocatalysts (where M is Mn, Fe and/or Co) has been common practice for decades to induce electron hole and/or oxygen vacancy formation and thus enhance electrochemical activity. However, Sr segregation at electrocatalyst surface, forming insulative SrO/Sr(OH) 2 /SrCO 3 phases and diminishing electrochemical activity, due to cation size mismatch and electrostatic forces, is a major issue. Considering that Sr segregation can cover a significant portion of the perovskite surface, mostly preventing oxygen contacting the perovskite surface and rendering the perovskite bulk devoid of Sr dopant, in this work, it is hypothesized that abandoning Sr doping altogether may be a viable option to develop SOC oxygen electrodes. Structural, surface-chemical, microstructural and electrochemical characterizations performed on single-phase perovskite and perovskite-ionic conductor nanocomposite films, all fabricated from liquid precursors, show that, while Sr doping stabilizes the microstructure and generates a certain amount of oxygen vacancies at perovskite surfaces, it also induces SrCO 3 and Ruddlesden-Popper phase formation, which yields lower electrochemical performance than the Sr-free perovskites when both are used in composite form. Sr-free perovskites introduced here can potentially avoid segregation-induced performance loss and contribute to faster commercialization of SOCs.