High Performance Non-precious Metal Electrocatalysts Derived From MOF Towards Oxygen Reduction Reaction

Fuel cells(FCs),as its environmental friendly,efficient energy conversion and facile preparation method,show promise for the replacement of gasoline internal-combustion engines for vehicle propulsion and other applications.Owing to the sluggish kinetics of a cathodic oxygen reduction reaction(ORR)in these devices,efficient ORR electrocatalysts are demanded for practical applications.At present,Pt-based materials are the most efficient ORR catalysts used in FCs,while their low abundance,high cost,poor durability consist in a main obstacle in the development of FCs.To overcome this problem,the exploration of non-precious metal ORR catalysts has been extensively conducted in recent years.Recently,metal organic frameworks(MOFs),linking organic and inorganic moieties through covalent coordination linkages,have aroused wide interest in various applications.Thanks to their diverse structures and unprecedented advantages regarding high surface area,large pore volume as well as various pore sizes,MOFs have been regarded as an alternative precursor to construct nanoporous carbon materials,which intrigue their broad applications in electrochemical energy storage.In this work,two kinds of non-precious metal ORR catalysts with high activity and durability have been synthesized by using the MOF as a precursor.(1)By doping iron into isoreticular metal organic framework-3(IRMOF-3)as a precursor and then annealing at 900 oC under inert gas atmosphere,we have successfully prepared high efficient electrocatalyst of Fe/IRMOF-3-900.The electrocatalytic properties of the Fe/IRMOF-3-900 towards oxygen reduction reaction(ORR)are investigated by using rotating ring disk electrode(RRDE).The results demonstrate that the 1%Fe/IRMOF-3-900 exhibits the highest ORR activity: the onset and half-wave potentials are measured at 1.02 V and 0.88 V vs.RHE,respectively,together with electron transfer number of 3.90 at 0.4 V,kinetic current density of 4.5 mA cm-2 at 0.88 V,and excellent longtime stability in alkaline solution.Such high ORR activity is superior to many MOFs derived noble metal free electrocatalysts reported so far,and attributed to that the 1%Fe doped could retain the well-defined cubic morphology of the IRMOF-3,resulting in high surface area and large total pore volume,high nitrogen content and high density of electrocatalytic active N-species.(2)By microwave-assisted synthesis of MIL-101(Fe)nanoparticles and using polyaniline(PAni)polymers as nitrogen source,fully stirred and mixed according to proportion of MIL-101(Fe)and PAni,and then carbonized at 900 oC under N2 flow twice,we have successfully prepared MOF/PAni-x electrocatalyst.The ORR performances of the MOF/PAni-x are investigated by using rotating disk electrode(RDE).When the weight ratio of MIL-101(Fe)and PAni was 1:8(denoted MOF/PAni-8),the catalyst exhibits the highest ORR activity: the onset and half-wave potentials are measured at 1.040 V and 0.916 V vs.RHE,respectively,together with electron transfer number of 4.0 at 0.4 V,and excellent longtime stability in alkaline solution.The excellent ORR performance is mainly attributed to the stable core shell structure,large specific surface area and high content of electrocatalytic active N-species.