Intercalating MnO₂ Nanosheets With Transition Metal Cations to Enhance Oxygen Evolution

The catalytic activity of MnO 2 nanosheets towards oxygen evolution depends highly on their interlayer environment. We present a systematic investigation on fine‐tuning of the interlayer environment of MnO 2 nanosheets by intercalation through a facile cation exchange with inexpensive first‐row transition metal cations, including Ni 2+ , Co 2+ , Cu 2+ , Zn 2+ , and Fe 3+ ions. Among them, the Ni‐intercalated MnO 2 nanosheets show remarkably enhanced OER activity and long‐term stability, compared to pristine MnO 2 nanosheets. The overpotential of 330 mV at a current density of 10 mA cm −2 is observed for the Ni‐intercalated MnO 2 nanosheets. The ehancement mechanism of OER is studied by comparing physiochemical properties, such as the oxidation state of Mn, the interlayer distance, the increase in the disorder/twisting of MnO 6 octahedra, and the interlayer cooperative binding of water molecules. The Ni intercalation, different from other metal cations, strengthens the Mn−O bond perpendicularly to the layer chains to facilitate the interlayer catalysis possibly between two Mn sites, and thus promotes the efficiency of oxygen evolution.