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 CoSx@ 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 ( Eonset) of 0.923 V and half-wave potential ( E1/2) 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.

ZIF67-derived ultrafine Co9S8 nanoparticles embedded in nitrogen-doped hollow carbon nanocages for enhanced performances of trifunctional ORROERHER and overall water splitting
    Abstracts
    1 Introduction
    2 Experiments
        2.1 Synthesis of Co9S8@N-HC catalysts
        2.2 Material characteristics
        2.3 Electrochemical characteristics
    3 Results and discussion
    4 Conclusions
    Acknowledgements 
    References

• Quoc Hao Nguyen(Department of Chemical Engineering (Integrated Engineering), Kyung Hee University, 1732, Deogyeong‑daero, Giheung‑gu, Yongin‑si, Gyeonggi‑do 17104, Republic of Korea)
• Kyungmin Im(Department of Chemical Engineering (Integrated Engineering), Kyung Hee University, 1732, Deogyeong‑daero, Giheung‑gu, Yongin‑si, Gyeonggi‑do 17104, Republic of Korea)
• Thach N. Tu(Department of Chemical Engineering (Integrated Engineering), Kyung Hee University, 1732, Deogyeong‑daero, Giheung‑gu, Yongin‑si, Gyeonggi‑do 17104, Republic of Korea, Nguyen Tat Thanh University, 300A Nguyen Tat Thanh Street, District 4, Ho Chi Minh 755414, Vietnam)
• Jongwook Park(Department of Chemical Engineering (Integrated Engineering), Kyung Hee University, 1732, Deogyeong‑daero, Giheung‑gu, Yongin‑si, Gyeonggi‑do 17104, Republic of Korea)
• Jinsoo Kim(Department of Chemical Engineering (Integrated Engineering), Kyung Hee University, 1732, Deogyeong‑daero, Giheung‑gu, Yongin‑si, Gyeonggi‑do 17104, Republic of Korea) Corresponding author