An active site pre-anchoring and post-exposure strategy in Fe(CN)64-@PPy derived Fe/S/N-doped carbon electrocatalyst for high performance oxygen reduction reaction and zinc-air batteries

A novel “active site pre-anchoring and post-exposure” strategy is developed for the synthesis of highly active Fe/3S/N-C ORR electrocatalyst. In the synthesis of Fe/3S/N-C, the Fe(CN)64-@PPy precursors with highly dispersion of Fe active species were initially created by pre-anchoring Fe(CN)64- into polypyrrole (PPy) matrixes through electrostatic interactions depending on the cation radicals generated on the PPy chains during pyrrole monomer polymerization. The Fe(CN)64-@PPy then suffered pyrolysis treatment in the presence of sublimed sulfur activator that ensures a larger specific area and thus effective exposure of Fe and N active sites in Fe/3S/N-C. Depending on highly efficient dispersion of Fe3C and Fe-Nx active species, the resultant Fe/3S/N-C electrocatalyst displays 20 mV higher onset potential (0.99 V) and 50 mV higher half-wave potential (0.89 V) than those of a commercial Pt/C catalyst in an alkaline medium. This, combined with high current density (–5.71 mA cm−2) and excellent durability (larger than 95% retention after 20000 s), are one of the best performance among non-precious metal ORR electrocatalysts reported thus far. In addition, Fe/3S/N-C employed as the cathode material for zinc-air battery, shows excellent durability and superior peak power density to Pt/C. A series of control experiments combined with DFT theoretical analysis demonstrated that the Fe3C nanoparticles boost the activity of Fe-Nx species in Fe/3S/N-C, meanwhile the coexistence of Fe3C and Fe-Nx active species increased the HOMO energy level and O2 adsorption energy of the catalyst. These result in improved ORR performance.