In situ embedding Co9S8 into nitrogen and sulfur codoped hollow porous carbon as a bifunctional electrocatalyst for oxygen reduction and hydrogen evolution reactions

The oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) are critical processes for many energy conversion technologies, where efficient catalyst plays a key role in these reactions. Here we report a novel in situ strategy to embed Co9S8 nanoparticles (NPs) into nitrogen and sulfur codoped hollow porous carbon (Co9S8@N-S-HPC). In this strategy, the ZIF-8 surface is firstly decorated by cobalt thiourea, and then coated with a shell of polymeric resorcinol-formaldehyde, followed by a high temperature pyrolysis treatment. The resulting Co9S8@N-S-HPC shows comparable catalytic activity for ORR compared with commercial 20 wt% Pt/C catalyst and superior long-term stability under alkaline conditions. Simultaneously, Co9S8@N-S-HPC also exhibits an excellent HER activity with low onset overpotential of 68 mV, a small Tafel slope of 78 mV per decade and a long-term durability in alkaline medium. First-principles calculations reveal that Co9S8 particle can anchor in NS-HPC via a Co-S bond and enhance the binding of Co9S8 and N-S-HPC. The N-S-HPC can affect the electronic structure of supported Co9S8 strongly. The combined experimental and theoretical investigation show the outstanding ORR and HER performances of Co9S8@N-S-HPC are attributed to its unique nanostructure and synergistic interactions between Co9S8 NPs and N-S-HPC.