An Fe-N/S-C hybrid electrocatalyst derived from bimetal-organic framework for efficiently electrocatalyzing oxygen reduction reaction in acidic media

Abstract Heteroatoms doped Fe-N-C electrocatalysts have been widely acknowledged as one of the most promising candidates to replace Pt-based materials for electrocatalyzing oxygen reduction reaction (ORR). However, the complicated synthesis method and controversial catalytic mechanism represent a substantial impediment as of today. Herein, a very facile strategy to prepare Fe-N/S-C hybrid through pyrolyzing Zn and Fe bimetallic MOFs is rationally designed. The electrocatalytic ORR performance shows a volcano-type curve with the increment of added Fe content. The half-wave potential (E1/2) for ORR at optimized Fe-N/S-C-10% (10% = n (Fe)/(n (Fe) + n (Zn)), n (Fe) and n (Zn) represent the moles of Fe2+ and Zn2+ in the precursors, respectively) shifts significantly to the positive direction of 19.6 mV with respect to that of Pt/C in acidic media, as well as a high 4e selectivity and methanol tolerance. After 10,000 potential cycles, E1/2 exhibits a small negative shift of ~27.5 mV at Fe-N/S-C-10% compared favorably with Pt/C (~141.0 mV). This can be attributed to: i) large specific surface area (849 m2/g) and hierarchically porous structure are favorable for the rapid mass transfer and active sites exposure; ii) the embedded Fe-containing nanoparticles in porous carbon are difficult to be moved and further agglomerated during the electrochemical accelerated aging test, further improving its stability; iii) there exist small Fe-containing nanoparticles, uniformly doped N and S, abundant Fe-N as efficiently active sites. This work represents a breakthrough in the development of high-efficient non-precious-metal catalysts (NPMCs) to address the current Pt-based electrocatalysts challenges.