The high overpotential of the Oxygen Evolution Reaction (OER) in water splitting hampers hydrogen production efficiency. While most OER catalysts follow the sluggish Adsorbate Evolution Mechanism (AEM), the newly discovered Lattice Oxygen Mediated (LOM) mechanism offers a more efficient pathway by involving redox-active lattice oxygen, drastically reducing overpotentials. However, the LOM reaction mechanism is poorly understood. Our research focuses on different phases of Co-based perovskite oxides to understand how a shift from AEM to LOM is fundamentally influenced by changes in Co-O bonding environment in different crystal phases rather than dopants. We will use Operando High Energy Resolution Fluorescence Detection-X-ray Absorption Fine Structure (HERFD-XAFS) to study the Co K Edge, monitoring evolution in coordination environment and electronic structure in the catalyst bulk under different voltages. This study aims to elucidate how crystal phase affects LOM activity