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) encapsulated Fe doped Co₉S₈ nanoparticles are successfully synthesized by direct pyrolysis of S, Co, and Fe-based polypyrrole (S–Co–Fe-PPYs) precursors for efficient overall water splitting. Specifically, the optimal catalyst (Fe_0-33-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 Fe_0-33-Co₉S₈@SNOPC can be credited to the synergistic effect produced by Fe doped Co₉S₈ core and multi-atom incorporated porous carbon shell.