Nitrogen-doped carbon spheres decorated with CoSx nanoparticles as multifunctional electrocatalysts for rechargeable zn-air battery and overall water splitting

The anchoring of CoSx nanoparticles with N-doped carbon spheres shows excellent multifunctional activities of electrocatalytic ORR, HER, and OER, demonstrating the potential applications in rechargeable Zn-air battery and water-splitting electrolyzer. [Display omitted] •N-doping into biomass-derived carbon spheres prevent the overgrowth of CoSx nanoparticles.•N-doping evidently improves the hydrophilicity of carbon spheres.•The resulting CoSx/NCS shows good multifunctional electrocatalytic activity for HER, OER, and ORR.•The CoSx/NCS performs well in a real Zn-air battery and water-splitting setup. Developing non-precious multi-functional electrocatalysts for oxygen reduction reaction (ORR), oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) to replace noble metal (Pt, Ru, Ir, etc) is one of the most important directions in the field of energy conversion and storage. Herein, we successfully prepared CoSx nanoparticles loaded onto N-doped carbon spheres to form unique CoSx/NCS nanocomposites, showing good tri-functional activities for ORR, OER and HER. As the cathodic electrocatalyst in Zn-air battery, the CoSx/NCS shows a lower charge voltage of 2.1 V and a high power density of 72.7 mW cm−2 compared to Pt/C. CoSx/NCS also shows potentials in overall water splitting as the OER and HER electrocatalysts. The onset potential and overpotential at 10 mA cm-2 toward overall water splitting reaches 1.70 V and 1.83 V, respectively. The enhanced activity of CoSx/NCS should be ascribed to the synergistic effects of improved surface hydrophilicity, Co-N sites, pyridinic-N species, and Co-S bonds. This study provides a new strategy to synthesize active electrocatalysts with multiple functions in energy conversion and storage.