Due to the sluggish kinetics of the oxygen reduction reaction (ORR) by non-Pt based catalyst, high loading of catalyst is required to achieve satisfactory fuel cell performance, which inevitably leads to the increase of the catalyst layer thickness with serious mass transport resistance. Herein, a defective zeolitic imidazolate framework (ZIF) derived Co/Fe-N-C catalyst with small mesopores (2-4 nm) and high density of CoFe atomic active sites are prepared by regulating the Fe dosage and pyrolysis temperature. Molecular dynamics simulation and electrochemical tests indicate that > 2 nm mesopores show insignificant influence on the diffusion process of O2 and H2 O molecules, leading to the high utilization of active sites and low mass transport resistance. The proton exchange membrane fuel cell (PEMFC) shows a high-power density of 755 mW cm-2 with only 1.5 mg cm-2 of non-Pt catalyst in the cathode. No apparent performance loss caused by concentration difference can be observed, in particular in the high current density region (1 A cm-2 ). This work emphasizes the importance of small mesopore design in the Co/Fe-N-C catalyst, which is anticipated to provide essential guidance for the application of non-Pt catalysts.
Keywords: defective zeolitic imidazolate frameworks (ZIFs); mass transport; mesopores; oxygen reduction reaction; proton exchange membrane fuel cells (PEMFCs).
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