Tuning Interactions between Layered Manganese Oxide and Intercalated Cations to Enhance Oxygen Evolution Reaction Activity

Layered manganese dioxide (MnO 2 ) stands out for its ability to act as a host for cation intercalation, which can significantly enhance its performance for the oxygen evolution reaction (OER). However, the role of intercalated cations in enhancing this reaction remains unknown. Herein, by systematically investigating various cation-intercalated (K +, Fe 3+, Co 2+, Ni 2+, and Cu 2+ ) layered manganese oxides, we demonstrate that the intercalated transition metal cations serve as the primary active sites. We find that the oxidation state of cations within the MnO 2 layers is determined by their relative Lewis acidity compared to the host Mn. This correlation between OER activity and the resulting electronic redistribution suggests that relative Lewis acidity of intercalated cations can determine the electronic redistribution between intercalated cations and MnO 2 layers, which in turn regulates the oxidation of both components. Therefore, we propose that relative Lewis acidity serves as a descriptor for OER activity. This work highlights the critical role of host-imposed electronic limits, establishing a rational design principle for future layered material-confined systems.