Preparation And Investigation Of MOFs-derived High-performance Single Atoms Doped Non-platinum Catalysts For Oxygen Reduction

Developing high-performance and low-cost non-precious metal carbon-based catalysts to replace commercial platinum catalysts towards oxygen reduction is of great significance,which can reduce costs and promote the commercial application of fuel cells.In this paper,high-performance oxygen reduction non-precious metal carbon-based catalysts have been successfully prepared by using metal-organic frameworks?MOFs?as precursors,doping with single transition metal atoms,tuning the pore structure and central metal elements,and optimizing the pyrolysis processes.The catalysts exhibited significantly improved performance towards oxygen reduction in acidic and alkaline media.The main research works could be described as below:A UIO-66-NH₂ derived multi-element?Fe,S,N?co-doped porous carbon catalyst,Fe/N/S-PC,was syntheisized by a double-solvent diffusion-pyrolysis method,in which the UIO-66-NH₂ was used as precursor,doping elements were highly dispersed on the surface and in the interior of micropores of the precursor through a double-solvent diffusion methode.The catalyst prepared through high tempertaure pyrolysis exhibits a well-defined mesoporous structure and highly dispersed doping elements.Actually,the morphology of the UIO-66-NH₂precursor is perfectly inherited by the derived carbon material,resulting in a high surface area,a well-defined mesoporous structure,and atomic-level dispersion of the doping elements.Fe/N/S-PC demonstrates outstanding catalytic activity and durability for the ORR in both alkaline and acidic solutions.In 0.1 M KOH,its half-potential reaches 0.87 V?vs.RHE?,30mV more positive than that of a 20 wt%Pt/C catalyst.In 0.1 M HClO₄,it reaches 0.785 V?vs.RHE?,only 65 mV less than that of Pt/C.The catalyst also exhibits excellent performance in acidic hydrogen/oxygen PEM fuel cells.An MEA with our catalyst as the cathode reaches 700mA·cm^–22 at 0.6 V and a maximum power density of 553 mW·cm^–2,which is in the rank of the best for the doped carbon catalysts reported up to now.Furthermore,another non precious metal catalyst was prepared by using a two-dimensional MOF as precursor,in which the central metal atom Zn was replaced partly by Fe to realize the doping of Fe atoms.With carbon nitride g-C₃N₄ as promoter and stabilizer of single Fe atoms,the content of single Fe atoms in the prepared porous carbon nanosheet catalyst?Fe-SA/N-PCNs?is up to 3.89wt%.The Fe-SA/N-PCNs catalyst shows excellent oxygen reduction catalyst activity and stability in both alkaline and acidic media.In 0.1M KOH solution,the half-wave potential of Fe-SA/N-PCNs reaches 0.86 V?vs.RHE?,which is20 mV higher than that of commercial Pt/C;in 0.1 M HClO₄ solution,the half-wave potential of the catalyst reaches 0.79 V?vs.RHE?,close to the performance of commercial Pt/C catalysts.The durability of Fe-SA/N-PCNs for the ORR is superior than that of Pt/C catalysts in both alkaline and acidic solutions.Based on the charactrization results,it is found that the addition of g-C₃N₄ plays an crucial role for the high single Fe content and high performance of the catalyst.