D-band center modulation of atomic dispersed FeNx sites by incorporating Co9S8 nanoparticles towards augmented ORR/OER electrocatalysis in Zn-air batteries

Atomically dispersed Fe-N-C catalysts have currently received extremely widespread attention as one of encouraging candidates for Pt-based oxygen reduction reaction (ORR) catalysts owing to their high intrinsic activity and atomic utilization efficiency as well as the affluent reserve, but further optimizing the adsorption behaviors of the primitive FeN_x sites in Fe-N-C for oxygen-related intermediates is significant for bifunctional oxygen catalytic performances to propel their applications for reversible Zn-air battery. Herein, Co₉S₈ nanoparticles incorporated into atomic Fe dispersed N-enriched porous graphene carbon aerogels (Co₉S₈/Fe-N-C) were fabricated via two rounds of hydrothermal treatment followed by high-temperature pyrolysis. DFT calculations and experimental investigation revealed that, in virtue of the strong interactions effect between Co₉S₈ nanoparticles and Fe-N-C, the regulated electronic structure of Co₉S₈/Fe-N-C and the introduced abundant sulfur vacancies induced the d-band center modulation of FeN_x sites closer to the Fermi level, which can optimize the binding energy for oxygen-containing intermediates, thereby endowing the catalyst with enhanced bifunctional catalytic performance. Therefrom, the Co₉S₈/Fe-N-C catalyst presented efficient bifunctional ORR/OER activity with a narrower ΔE (0.68V), outstripping the Pt/C + RuO₂ catalysts. Additionally, the Zn-air battery assembled with Co₉S₈/Fe-N-C delivered a large specific capacity (798 mAh g_Zn⁻¹) with a power density of 103 mW cm⁻² and a long-term stability over 140 h. This research presents an innovative perspective on theoretical design of highly efficient atomically dispersed Fe based catalysts for reversible Zn-air battery.