An in situ spectroelectrochemical technique was applied to MnO2 oxygen evolution electrocatalysts with different crystal structures (alpha-MnO2 and (beta-MnO2) to monitor the Mn(3+ )intermediate in the presence of pyridine. Upon the addition of pyridine to the electrolyte, the UV-vis signal of Mn3+ disappeared on beta-MnO2 while remaining on alpha-MnO2. Electrochemical and spectroscopic analysis confirmed that pyridine accelerated interfacial charge transfer between the electrolyte and the MnO2 surface by coordinating to the MnO6 octahedra, triggering more activity enhancement than alpha-MnO2.