Nickelate (e.g. Pr₂NiO₄) exhibits high activity towards the oxygen reduction reaction over a wide temperature range (600 - 900 ^oC), which makes it a promising candidate as an advanced cathode for solid oxide fuel cells. However, a phase transition occurs in Pr₂NiO₄ during cell operation, following: Pr₂NiO₄ à Pr₆O₁₁ + Pr₃Ni₂O₇. As a result, the quantification of the degree of phase transformation becomes necessary to understand the structure-electrochemical property relationship. In this presentation, we report our recent work on (1) replacing the oxide current collector with a gold metal grid, which enables the cathode to expose to the x-ray beam. The x-ray analysis was performed at room temperature and (2) utilizing in situ capability to study the kinetics and mechanisms of phase evolution and establishing the relationship between high-temperature structures and the electrochemical performance. Finally, we will compare the XRD results acquired from room temperature with these in situ studies.