Heterostructure CoFe@(Co0.5Fe0.5)S@NCNT anchored on rice husk-based hierarchical porous carbon as a bifunctional cathode catalyst for Zn–air batteries

Efficient, low-cost cathode catalysts featuring highly dispersed, active sites are pivotal for advancing metal–air batteries. In this study, a bifunctional catalyst was developed using rice husk-based porous carbon (RHPC) with a hierarchical porous structure, comprising a multilayer heterostructure integrating nanoscale CoFe@(Co0.5Fe0.5)S wrapped with nitrogen-doped carbon nanotubes (NCNTs). XRD and TEM images reveal the formation of a CoFe alloy on the RHPC surface and pores, catalyzing the growth of uniform-diameter NCNTs. XPS analysis demonstrates an electron-donating effect on the surface pyridinic-N structure upon introducing the sulfide intermediate layer. Theoretical simulations substantiate these discoveries, emphasizing diminished adsorption of *OH and *OOH, substantially reducing overpotentials for both the ORR by 21 mV and OER by 46 mV compared to CoFe@NCNT/RHPC lacking the sulfur element. This results in CoFe@(Co0.5Fe0.5)S@NCNT/RHPC emerging as an exceptionally effective bifunctional catalyst (ΔE = 0.614 V). Integration into a rechargeable zinc–air battery showcases a peak power density of 136.0 mW cm−2. The unique morphology design and electronic structure optimization significantly improve the catalytic performance.