ZIF67-derived ultrafine Co9S8 nanoparticles embedded in nitrogen-doped hollow carbon nanocages for enhanced performances of trifunctional ORR/OER/HER and overall water splitting

Electrochemical oxidation and reduction reactions are fundamental in various conversion and energy storage devices. Functional materials derived from MOFs have been considered promising as electrical catalysts for ORR, HER, and OER, which can be used in Zinc-air batteries and water electrolysis. Herein, we designed a novel approach to fabricating the ultrafine Co₉S₈ embedded nitrogen-doped hollow carbon nanocages (Co₉S₈@N-HC). The method involved a process of sulfidation of cobalt-based metal–organic frameworks (ZIF67) and then coating them with polypyrrole (PPy). PPy has notable properties such as high electrical conductivity and abundant nitrogen content, rendering it highly promising for catalytic applications. The Co₉S₈@N-HC catalyst was successfully synthesized via the carbonization of CoS_x@PPy. Remarkably, the Co₉S₈@N-HC catalyst demonstrated exceptional electrocatalytic activity, requiring only low overpotentials of 285 mV and 201 mV at 10 mA cm^‒2 for OER and HER, respectively, and exhibited high activity for ORR, with an onset potential (E_onset) of 0.923 V and half-wave potential (E_1/2) of 0.879 V in alkaline media. The electrocatalytic efficiency displayed by Co₉S₈@N-HC opens a new line of research on the synergistic effect of MOF-PPy materials on energy storage and conversion.