It is shown that producing PrBaCO₂O_5+δ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_2+δ nanoparticle by a scalable synthesis method leads to high mass activities for the oxygen evolution reaction (OER) with outstanding improvements by 10× and 50×, respectively, compared to those prepared via the state-of-the-art synthesis method. Here, detailed comparisons at both laboratory and industrial scales show that Ba_0.5Sr_0.5Co_0.8Fe_0.2O_2+δ appears to be the most active and stable perovskite catalyst under alkaline conditions, while PrBaCO₂O_5+δ reveals thermodynamic instability described by the density-functional theory based Pourbaix diagrams highlighting cation dissolution under OER conditions. Operando X-ray absorption spectroscopy is used in parallel to monitor electronic and structural changes of the catalysts during OER. The exceptional BSCF functional stability can be correlated to its thermodynamic meta-stability under OER conditions as highlighted by Pourbaix diagram analysis. BSCF is able to dynamically self-reconstruct its surface, leading to formation of Co-based oxy(hydroxide) layers while retaining its structural stability. Differently, PBCO demonstrates a high initial OER activity while it undergoes a degradation process considering its thermodynamic instability under OER conditions as anticipated by its Pourbaix diagram. Overall, this work demonstrates a synergetic approach of using both experimental and theoretical studies to understand the behavior of perovskite catalysts.