Lignin-based nitrogen/sulfur dual-doped nanosheets decorated with Co1−xS nanoparticles as efficient bifunctional oxygen electrocatalysts

The development of efficient, cost-effective, bifunctional cathode catalyst materials to replace precious metals is highly attractive for the fabrication of Zn-air battery. Here, the three-dimensional N and S co-doped carbon nanosheets loaded with cobalt sulfide nanoparticles (Co1-xS@SNFC) for bifunctional oxygen electrocatalysis were synthesized with Co(NO3)2·6H2O as the Co source, lignin as the carbon source, thiourea as the nitrogen/ sulfur source, and MgO as the template. The synergistic effect of multiple active sites gives the Co1-xS@SNFC fast electrochemical kinetic properties and excellent stability to oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The half-wave potential and overpotential of Co1-xS@SNFC were 0.84 mV and 306 mV, respectively, which is closed to commercial noble metal catalysts. In addition, Co1-xS@SNFC exhibited four-electron transfer characteristics and ultra-low tafel slope. Compared with commercial Pt/C, the Zn-air battery assembled from Co1-xS@SNFC exhibited a low voltage gap of polarization curve (0.75 V) between charging and discharge and high power density (207 mWcm-2) in alkaline electrolyte. This work developed a green and novel fabrication approach for the synthesis of bifunctional electrocatalyst and provides a new idea for high-value utilization of biomass.