Structure-engineered bifunctional oxygen electrocatalysts with Ni3S2 quantum dot embedded S/N-doped carbon nanosheets for rechargeable Zn-air batteries

• Ni 3 S 2 -QDs/SNC nanocomposite was firstly designed and fabricated. • The authentic role of Ni 3 S 2 -QDs has been demonstrated by the various test. • The electrocatalyst shows excellent catalytic activity with ORR and OER. • The zinc-air battery shows a high power density and excellent rechargeability. The rational design of a high-efficiency and low-cost bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is significant but challenging for energy conversion devices such as Zn-air battery, fuel cell and water splitting. Herein, a two-dimensional heterostructure of S/N co-doped carbon nanosheets decorated with ultrafine Ni 3 S 2 quantum dots (Ni 3 S 2 -QDs/SNC) is designed and fabricated via a facile hydrothermal and high-temperature pyrolysis procedures. The heterostructure of Ni 3 S 2 -QDs/SNC is in situ formed from the Ni 3 S 2 QDs without sulfidation. Meanwhile, the S/N co-doped carbon carrier dramatically enhances the electrical conductivity and creates more effective active sites for ORR and OER. As a result, the Ni 3 S 2 -QDs/SNC affords a half-wave potential of 0.864 V for ORR and an overpotential of 0.310 V at 10 mA cm −2 for OER, outperforming the benchmark of Pt/C and RuO 2 . Moreover, the assembled Zn-air battery with Ni 3 S 2 -QDs/SNC air cathode exhibits a high power density (212 mW cm −2 ), energy density (962 Wh kg Zn − 1 ), and satisfactory stability (more than 200 h), which are superior than those of Pt/C-based Zn-air battery. Density functional theory calculations further illustrate that the interfacial Ni site of Ni 3 S 2 -QDs/SNC exhibits enhanced capacities for both the ORR and OER. This approach provides a novel strategy for the exploration of high-performance bifunctional oxygen electrocatalysts for energy-related applications.