Synthesis of heteroatom incorporated porous carbon encapsulated Fe-doped Co9S8 as an efficient bifunctional electrocatalyst for overall water splitting

Doping metal ions into cobalt sulfide is a promising strategy to improve its performance as a cheap, green, highly active and sustainable electrocatalyst for overall water splitting. Herein, cauliflower-like, noble metal-free bifunctional electrocatalysts composed of S, N, and O atoms co-incorporated porous carbon (SNOPC) encapsu-lated Fe doped Co9S8 nanoparticles are successfully synthesized by direct pyrolysis of S, Co, and Fe-based pol-ypyrrole (S-Co-Fe-PPYs) precursors for efficient overall water splitting. Specifically, the optimal catalyst (Fe0-33- Co9S8@SNOPC) shows excellent electrocatalytic performance in an alkaline electrolyte, requiring ultra-low overpotentials of 275 and 258 mV to reach a current density of 10 mA cm-2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively, with exceptional stability for 50 h. Furthermore, when applied for overall water splitting as a bifunctional electrolyzer, it generates a current density of 10 mA cm-2 at an extremely low cell voltage of 1.595 V. The exceptional electrocatalytic activity of Fe0-33-Co9S8@S- NOPC can be credited to the synergistic effect produced by Fe doped Co9S8 core and multi-atom incorporated porous carbon shell.

Automated summary

Doping metal ions into cobalt sulfide is a promising strategy to enhance its electrocatalytic performance for overall water splitting. The synthesis of noble metal-free bifunctional electrocatalysts, composed of S, N, and O atoms co-incorporated porous carbon encapsulated Fe doped Co9S8 nanoparticles, is achieved by direct pyrolysis of S, Co, and Fe-based polypyrrole precursors. The optimal catalyst (Fe0-33-Co9S8@SNOPC) exhibits outstanding electrocatalytic activity in an alkaline electrolyte, with ultra-low overpotentials and exceptional stability for oxygen and hydrogen evolution reactions, as well as an extremely low cell voltage for overall water splitting.