Mesoporous Fe-N_x-C Sub-Microspheres for Highly Efficient Electrocatalytic Oxygen Reduction Reaction

We design and obtain mesoporous Fe-N_x-C sub-microspheres (Meso Fe-N_x-C-SS) using the amino acid-metal complex as Fe/N/C precursor and mesoporous silica sub-microspheres (MSS) as hard template by a facile template-assistance strategy. The Histidine-Fe complex is impregnated into mesopores of MSS, and then Meso Fe-N_x-C-SS are obtained by high-temperature carbonization process and removal of MSS template. The as-fabricated Meso Fe-N_x-C-SS exhibits the spherical structure with rough surface with the diameter size of 200–500 nm. And Meso Fe-N_x-C-SS also possesses a high specific surface area of 784 m² g⁻¹, a large pore volume of 1.65 cm³ g⁻¹, and a large pore size in the range of 10–22 nm. Benefiting from atomically dispersed N-coordinated Fe and unique three-dimensionally (3D) interconnected mesoporous carbon architecture, Meso Fe-N_x-C-SS shows excellent electrocatalytic performance toward oxygen reduction reaction (ORR) with positive half-wave potential (E_1/2 0.86 V), high stability (93.94 % after 30,000 s), low Tafel slop (43 mV dec⁻¹) and good methanol tolerance, exceeding commercial Pt/C catalyst in alkaline media. As the cathode catalyst within the primary Zn-air batteries, Meso Fe-N_x-C-SS also reveals an outstanding catalytic activity (the maximum power density of 120 mW cm⁻²) and superior discharge stability (at current density of 10 mA cm⁻² after 6 cycles, at different current densities of 5, 10, 20 mA cm⁻²), promoting its practical application in Zn-air batteries.