In this presentation, I will use the cathode for solid oxide fuel cells as an example to elucidate the relationship between the phase stability and electrochemical activity. The presentation will focus on praseodymium nickelate (Pr₂NiO₄), an active electrode for oxygen reduction reaction. Pr₂NiO₄, however, exhibits phase transition at elevated temperatures or under an electrochemical operation to form PrO_x and higher ordered nickelate phase. We will discuss multiple strategies to improve the phase stability via intrinsic dopants and microstructure modification. More importantly, the knowledge gained has been translated to develop accelerated test protocols for nickelate- and perovskite-based cathodes.