This study investigates the electrocatalytic water oxidation mechanism using manganese phosphates, specifically KMnPO₄ and KMnPO₄·H₂O, which have 4-coordinated and 6-coordinated Mn centers, respectively. The research aims to understand the structural and catalytic performance relationship in Mn-based systems. The study reveals that during water oxidation, Mn(III), Mn(IV), and Mn(V) intermediate species are present, with Mn(V)=O being crucial for O-O bond formation. In KMnPO₄·H₂O, the Mn coordination structure remains stable, while in KMnPO₄, it changes from 4-coordinated [MnO₄] to 5-coordinated [MnO₅], which is thermodynamically favorable for retaining Mn(III)-OH and generating Mn(V)=O. The Mn(V)=O species is in equilibrium with Mn(IV)=O, and its concentration determines the intrinsic activity of water oxidation. The study also shows that KMnPO₄ exhibits higher catalytic activity than KMnPO₄·H₂O. Through various techniques, including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, the study confirms the role of Mn(V)=O in water oxidation and the structural flexibility of [MnO₅] in retaining Mn(III)-OH and generating Mn(V)=O. The results provide a clear understanding of the water oxidation mechanism in Mn-based systems.This study investigates the electrocatalytic water oxidation mechanism using manganese phosphates, specifically KMnPO₄ and KMnPO₄·H₂O, which have 4-coordinated and 6-coordinated Mn centers, respectively. The research aims to understand the structural and catalytic performance relationship in Mn-based systems. The study reveals that during water oxidation, Mn(III), Mn(IV), and Mn(V) intermediate species are present, with Mn(V)=O being crucial for O-O bond formation. In KMnPO₄·H₂O, the Mn coordination structure remains stable, while in KMnPO₄, it changes from 4-coordinated [MnO₄] to 5-coordinated [MnO₅], which is thermodynamically favorable for retaining Mn(III)-OH and generating Mn(V)=O. The Mn(V)=O species is in equilibrium with Mn(IV)=O, and its concentration determines the intrinsic activity of water oxidation. The study also shows that KMnPO₄ exhibits higher catalytic activity than KMnPO₄·H₂O. Through various techniques, including X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT) calculations, the study confirms the role of Mn(V)=O in water oxidation and the structural flexibility of [MnO₅] in retaining Mn(III)-OH and generating Mn(V)=O. The results provide a clear understanding of the water oxidation mechanism in Mn-based systems.