Bimetal Zeolitic Imidazolite Framework-Derived Iron‑, Cobalt- and Nitrogen-Codoped Carbon Nanopolyhedra Electrocatalyst for Efficient Oxygen Reduction

Abstract

Replacing precious metal electrocatalysts with high-performance and low-cost nonprecious metal electrocatalysts (NPMCs) is crucial for the commercialization of fuel cell technologies. Herein, we present a novel and facile route for synthesis of iron-, cobalt-, and nitrogen-codoped carbon nanopolyhedra electrocatalysts (Fe,Co,N-CNP) by one-step pyrolysis of a new type of Fe/Co bimetal zeolitic imidazolate framework (Fe,Co-ZIF) crystals that were self-assembled by oxygen-free solvothermal reaction of Fe²⁺ and Co²⁺ with 2-methylimidazole. During the pyrolysis process, the Fe²⁺ ions in Fe,Co-ZIF not only effectively inhibit the aggregation of Co nanoparticles but also increase the specific surface area (SSA) and N content of the resultant electrocatalysts. The optimized Fe,Co,N-CNP(0.3) (Fe/Co molar ratio of 0.3 in Fe,Co-ZIF) electrocatalyst exhibited a highly promising activity for oxygen reduction reaction (ORR) with a positive half-wave potential (<i>E</i>_1/2) of 0.875 V (29 mV higher than that of the commercial Pt/C), excellent methanol tolerance, and electrochemical stability in the alkaline electrolyte. Also, Fe,Co,N-CNP(0.3) presents comparable ORR catalytic activity as Pt/C in the acidic electrolyte with <i>E</i>_1/2 of 0.764 V and superior methanol tolerance and electrochemical stability. The outstanding ORR performance of Fe,Co,N-CNP(0.3) is ascribed to the synergistic contribution of homogeneous Fe, Co, and N codoping structure, high SSA, and hierarchically porous structure for rapid mass transport. This novel and rational methodology for controlled synthesis of ZIFs-derived nitrogen-doped porous carbon nanopolyhedras offers new prospects in developing highly efficient NPMCs for ORR