Facile synthesis of coral branch-like porous catalyst based on covalent organic framework for efficient oxygen reduction reaction in direct formate fuel cell

Authors:
  • QLQianling Lu
    Qianling Lu
  • JWJiantao Wang
    Jiantao Wang
  • SWShaolong Wang
    Shaolong Wang
  • YLYang Li
    Yang Li
  • LHLinbin Hu
    Linbin Hu
  • SXShuai Xiao
    Shuai Xiao
  • QLQing Li
    Qing Li
  • JZJianhua Zeng
    Jianhua Zeng
  • MCMengjun Chen
    Mengjun Chen
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Abstract
The cathodic oxygen reduction reaction (ORR) represents a critical bottleneck in the practical performance of direct formate fuel cells (DFFCs), while the reliance on costly platinum catalysts impedes their widespread commercialization. In this study, we report the facile synthesis of coral branch-like porous Fe-N-C electrocatalysts employing a covalent organic framework (COF) as the support matrix and iron phthalocyanine (FePc) as the source of Fe and N. By modulating the FePc to COF mass ratio, the optimized catalyst, designated FePc1@COF5, exhibits an interconnected coral-shaped porous carbon architecture featuring homogeneously dispersed Fe–Nₓ active sites alongside in situ generated Fe2N and Fe3C nanocrystals. Comprehensive structural analyses reveal a high density of carbon defects and abundant pyridinic nitrogen and Fe–Nₓ moieties resulting from moderate FePc incorporation. Electrochemical evaluation via rotating disk electrode measurements demonstrates that FePc1@COF5 delivers superior ORR performance, with an onset potential of 0.929 V and a half-wave potential of 0.862 V versus the reversible hydrogen electrode (RHE), outperforming commercial 20 wt% Pt/C catalysts. The ORR proceeds predominantly through a four-electron transfer pathway and is characterized by a low Tafel slope of 27.62 mV dec⁻¹, indicative of rapid reaction kinetics. Electrochemical impedance spectroscopy further confirms reduced charge transfer and mass transport resistances. When employed as the air cathode in a membrane-less DFFC configuration, FePc1@COF5 achieves a peak power density of 24.9 mW cm⁻², surpassing that of the Pt/C cathode. This straightforward synthetic approach offers a promising route for the development of cost-effective, high-performance COF-based non-noble metal ORR catalysts suitable for application in DFFCs.

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