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

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 Ni3S2 quantum dots (Ni3S2-QDs/SNC) is designed and fabricated via a facile hydrothermal and high-temperature pyrolysis procedures. The heterostructure of Ni3S2-QDs/SNC is in situ formed from the Ni3S2 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 Ni3S2-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 RuO2. Moreover, the assembled Zn-air battery with Ni3S2-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 Ni3S2-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.

Automated summary

A high-efficiency and low-cost bifunctional electrocatalyst for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is designed and fabricated using two-dimensional heterostructure of S/N co-doped carbon nanosheets decorated with ultrafine Ni3S2 quantum dots (Ni3S2-QDs/SNC). The Ni3S2-QDs/SNC heterostructure is formed in situ from Ni3S2 QDs without sulfidation. The S/N co-doped carbon carrier enhances electrical conductivity and creates more active sites for ORR and OER. The Ni3S2-QDs/SNC exhibits better performance than Pt/C and RuO2 as a catalyst for ORR and OER, and the assembled Zn-air battery with Ni3S2-QDs/SNC air cathode shows improved power density, energy density, and stability compared to Pt/C-based Zn-air battery. Density functional theory calculations confirm the enhanced capacities of Ni3S2-QDs/SNC for both ORR and OER.