Systematic study of oxygen evolution activity and stability on La_1-xSr_xFeO_3-δ perovskite electrocatalysts in alkaline media

Perovskite oxide is an attractive low-cost alternative catalyst for oxygen evolution reaction (OER) relative to the precious metal oxide-based electrocatalysts (IrO₂ and RuO₂). In this work, a series of Sr-doped La-based perovskite oxide catalysts with compositions of La_1-xSr_xFeO_3-δ (x = 0, 0.2, 0.5, 0.8, and 1) are synthesized and characterized. The OER-specific activities in alkaline solution increase in the order of LaFeO_3-δ (LF), La_0.8Sr_0.2FeO_3-δ (LSF-0.2), La_0.5Sr_0.5FeO_3-δ (LSF-0.5), SrFeO_3-δ (SF), and La_0.2Sr_0.8FeO_3-δ (LSF-0.8). We establish a direct correlation between the enhancement in the specific activity and the amount of surface oxygen vacancies as well as the surface Fe oxidation states. The improved specific activity for LSF-0.8 is clearly linked to the optimum amount of surface oxygen vacancies and surface Fe oxidation states. We also find that the OER performance stability is a function of the crystal structure and the deviation in the surface La and/or Sr composition(s) from their bulk stoichiometric compositions. The cubic structure and lower deviation, as is the case for LSF-0.8, led to a higher OER performance stability. These surface performance relations provide a promising guideline for constructing efficient water oxidation.