Efficient bi-directional OER/ORR catalysis of metal-free C6H4NO2/g-C3N4: Density functional theory approaches

Abstract Metal-free catalyst with favorable advantages of nonpolluting, cost-effective and stable catalytic performances may be used in various redox reactions. In this paper, we design a series of C6H4NO2/g-C3N4 composites by combining a polar nitrobenzene molecule with g-C3N4 monolayer using density functional theory calculations. The electrocatalytic performances during oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are substantially improved thanks to the electron redistributions of g-C3N4 substrate. One composite specimen exhibits the lowest bi-directional OER/ORR overpotentials of 0.14/0.14 V, and the most stable composite specimen has OER/ORR overpotentials of 0.27/0.39 V. The number of active electrons in active atom, as descriptor of catalytic activity, can accurately estimate the OER and ORR activity of metal-free electrocatalysts. The modification strategy would be extended to design high-efficiency metal-free electrocatalysts.