Identifying the in situ protection role of MnO2 nanosheets on Co oxide for superior water oxidation

•Mn3+δ with stronger Lewis acidity prefer to accepted the electron was demonstrated as the origin of the in situ protection effect of MnO2 nanosheet.•Charge transfer from Mn to Co was confirmed by the XPS and DFT calculation.•With the modulation of Co electronic structure by Mn insertion and oxygen vacancies formation, in joint with the substantial surface area preserved from protection effect, the CMO-H300 sample exhibited excellent water oxidation activity in both alkaline and neutral medium.