Boosting the oxygen reduction performance of MOF-5-derived Fe-N-C electrocatalysts via a dual strategy of cation-exchange and guest-encapsulation

Abstract

MOF-5 is an excellent self-sacrificed template with fascinating advantages (e.g. thermal robustness, ultrahigh surface area) to prepare highly porous carbon materials for diverse applications but Fe-N-C catalysts derived from MOF-5 seem yet unexplored. Through a dual strategy of cation-exchange and guest-encapsulation, an excellent MOF-5-derived Fe-N-C electrocatalyst toward oxygen reduction reaction was accomplished involving three steps. First, bimetallic Fe/Zn-MOF-5 was obtained by solid-liquid cation exchange between MOF-5 and Fe(BF4)2 solution. Second, infiltration of imidazole molecules into the channels of MOF-5 was achieved via a wet impregnation method, giving the precursor of imidazole@Fe/Zn-MOF-5. Finally, pyrolysis of imidazole@Fe/Zn-MOF-5 under the optimal conditions produced a porous Fe-N-C carbon catalyst decorated by iron carbide (Fe3C) nanoparticles, which exhibits a better ORR catalytic performance (E1/2 = 0.86 V vs. RHE) and higher stability than the benchmark Pt/C in the alkaline electrolyte. Application in the homemade primary Zn-air battery as the cathode catalyst also achieves a maximum-power density of 85 mW cm−2, and a satisfactory durability (slight decay by 8.4% in voltage @ 5 mA cm−2 for 70 h). The current work provides a facile and general method to convert MOF-5 into efficient Fe-N-C catalysts with the tunable ORR performance, which may offer more insights into designing highly efficient MOF-derived Fe-N-C electrocatalysts toward ORR.