Hierarchical Fe-Mn binary metal oxide core-shell nano-polyhedron as a bifunctional electrocatalyst for efficient water splitting.

Electrochemical water splitting is convinced as one of the most promising solutions to combat the energy crisis. The exploitation of efficient hydrogen and oxygen evolution reaction (HER/OER) bifunctional electrocatalysts is undoubtedly a vital spark yet challenging for imperative green sustainable energy. Herein, through introducing a simple pH regulated redox reaction into a tractable hydrothermal procedure, a hierarchical FeO@MnO binary metal oxide core-shell nano-polyhedron was designed by evolving MnO wrapped FeO. The MnO effectively prevents the agglomeration and surface oxidation of FeO nano-particles and increases the electrochemically active sites. Benefiting from the generous active sites and synergistic effects of FeO and MnO, the FeO@MnO-NF nanocomposite implements efficient HER/OER bifunctional electrocatalytic performance and overall water splitting. As a result, hierarchical FeO@MnO only requires a low HER/OER overpotential of 242/188 mV to deliver 10 mA cm, a small Tafel slope of 116.4/77.6 mV dec, combining a long-term cyclability of 5 h. Impressively, by applying FeO@MnO as an independent cathode and anode, the overall water splitting cell supplies a competitive voltage of 1.64 V to achieve 10 mA cm and super long cyclability of 80 h. These results reveal that this material is a promising candidate for practical water electrolysis application.