Multi-layered active sites attached in 1D/3D hierarchical conductive network promote dioxygen fragmentation

Via the unique free radical polymerization induced hemin coated on PPy nanotubes as the first active site, and the double propionic groups of hemin served as an adsorption site and bound strongly to Co2+, inducing the growth of ZIF-67 with the second active site. Multi-layered active sites catalyst shows potential application for ORR. [Display omitted] •Novel multi-layered active sites Fe/Co-Nx can enhance oxygen reaction rate − determining steps.•The double propionic groups of Hemin served as adsorption site induced the growth of ZIF-67.•The Fe/Co-NC catalyst display highly efficient ORR performance and stability.•The Fe/Co-NC catalyst exhibit remarkable energy density and specific capacity for ZABs. The sluggish kinetic process of oxygen conversion reaction directly limits the energy density of Zn-air batteries (ZABs), construction of multi-layered catalytic active sites to promote dioxygen fragmentation is an urgent need for high-performance ZABs. Herein, a bead-like 1D/3D hierarchical conductive network catalyst (Fe/Co-NC) is fabricated, where polypyrrole nanotubes served as skeleton, its surface was coated with polymerized Hemin which have the first active site and double propionic groups as the adsorption sites for the formation of second site precursor of ZIF-67. We defined the Fe/Co-Nx derived by pyrolysis dispersed in 1D/3D structure as multi-layered active sites. Fe/Co-NC catalyst exhibits excellent catalytic performance (E1/2 = 0.86 V) and stability (the E1/2 loses 0.21 mV after 5000 cycles). After assembling to ZABs, the results show an inspiring peak power density of 238.6 mW cm−2, which is 1.8 times that of Pt/C catalyst. Density functional theory (DFT) indicates that multi-layered active sites can promoting dioxygen fragmentation rate − determining steps at higher limiting potential of 0.70 V. Partial density of states further demonstrates that multi-layered active sites with a downshift of the d-band center (-0.95 eV) weakens the adsorption of oxygen intermediates. Combined with conductivity calculations, density of states can reach higher levels, facilitating 4-electron transfer process.