Engineering active sites in ternary CeO-CuO-MnO heterointerface embedded in reduced graphene oxide for boosting water splitting activity.

The rational design of highly efficient and stable bifunctional catalysts for overall water splitting is vitally important. In this study, to increase the active catalytic sites of CeO for electrochemical water splitting, a ternary CeO-CuO-MnO heterostructure, synthesized by coprecipitation method, is loaded on reduced graphene oxide (rGO) nanosheets in different amounts to produce CeO-CuO-MnO@rGO nanocomposites. It is found that CeO-CuO-MnO@rGO nanocomposites show higher electrocatalytic activity than unsupported samples, and the best activity is observed when the wieght ratio of CeO-CuO-MnO is three times that of rGO. The CeO-CuO-MnO@rGO(3:1) requires low overpotentials of 130 and 270 mV for hydrogen and oxygen evolution reactions (HER and OER) at a current density of 10 mA cm. Furthermore, this material demonstrates a large electrochemically active surface area, low charge transfer resistance, suitable kintics, and high long-term stability for both OER and HER. Additionally, when CeO-CuO-MnO@rGO(3:1) is used as self-supported electrodes for the overall water splitting reaction, a low cell voltage of 1.68 V is obtained. This superior performance is due to: (i) active multi-metal sites that produce strong synergistic effects; (ii) the high conductivity of rGO, which faciliate favorable electron transfer; and (iii) the homogenous anchoring of CeO-CuO-MnO on rGO, which increases the number of active sites available on the catalyst surface.