Intercalating MnO2 Nanosheets With Transition Metal Cations to Enhance Oxygen Evolution

The catalytic activity of MnO2 nanosheets towards oxygen evolution depends highly on their interlayer environment. We present a systematic investigation on fine-tuning of the interlayer environment of MnO2 nanosheets by intercalation through a facile cation exchange with inexpensive first-row transition metal cations, including Ni2+, Co2+, Cu2+,Zn2+, and Fe3+ ions. Among them, the Ni-intercalated MnO(2 )nanosheets show remarkably enhanced OER activity and long-term stability, compared to pristine MnO2 nanosheets. The overpotential of 330 mV at a current density of 10 mAcm(-2) is observed for the Ni-intercalated MnO2 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 MnO6 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.