Preparation And Electrocatalytic Performance Of Graphene-based Composites For Oxygen Reduction Reaction

In this paper,graphene(GR)was used as the support materials,and we fabricated Pt nanoparticles modified porous graphene(Pt-Porous Graphene,Pt-PGR)composites,Iron(II)phthalocyanine(FePc)nanoclusters-graphene sandwich(FePc-Graphene,FePc-GR)composites and Fe-N-C nanoparticles modified porous graphene(Fe-N-C/Porous Graphene,Fe-N-C/PGR)composites respectively by designing the structure of materials using facile methords.The obtained composites exhibited three-dimensional interpenetrating porous structure or sandwich structure,which increased the surface area of the catalyst materials,prevented the aggregation of GR sheets or the supported nanoparticles and exposed more electrocatalytical active sites.The resulted composites were modified on electrode to investigate their electrocatalytic performance towards oxygen reduction reaction(ORR).A facile method was developed to fabricate Pt-PGR composites via impregnation and reduction.The porous graphene(PGR)was first immersed into a H2PtCl6 ethanol solution,and then the H2PtCl6 was reduced to Pt nanoparticles with NaBH4 to produce the Pt-PGR composites.The results indicated that the obtained Pt-PGR composites had three-dimensional interpenetrating porous structure,and the Pt nanoparticles from 50 to 150 nm uniformly distributed on the graphene surfaces.The Pt-PGR composites had excellent catalytical activity towards the ORR,and showed the higher diffusion-limited current densities(4.0 mA cm-2 at-0.6 V)and stability compared with the commercial 20%Pt/C catalyst.The calculated electron transfer number was 3.6,indicating an approximate four-electron process for the ORR.FePc nanoclusters were synthesized by solvent evaporation.Combining FePc nanoclusters with GR,the FePc-GR sandwich composites were produced.The results indicated that the FePc-GR composites exhibited sandwich structure,and the FePc nanoclusters(-500 nm)consisted of small nanoparticles were uniformly distributed between GR sheets.Compared with the pure FePc nanoclusters or GR,the FePc-GR composite showed improved electrocatalytical performance towards ORR,especially when the mass ratio of FePc nanoclusters to GR was 2:1,the obtained FePc-GR composites showed the highest current density.The electron transfer number of the FePc-GR composites was 4.05,indicating the direct four electron process for the ORR.In addition,the FePc-GR composites also exhibited good stability and excellent resistance to methanol compared with the commercial 20%Pt/C catalyst.Fe-N-C/PGR was synthesized from the pyrolysis of porous freeze-dried composites of FePc nanoclusters and graphene oxide(GO).By pyrolysis in argon atmosphere,the GO was reduced into GR,and the FePc nanoclusters were converted to Fe-N-C nanoparticles.The resules indicated that the Fe-N-C/PGR composites exhibited three-dimensional interpenetrated porous structure,and many particles with Fe-N-C active sites were distributed on the GR nanosheets.When the mass ratio of FePc nanoclusters to GO precursor was 3:1,the obtained Fe-N-C/PGR composites showed the highest electrocatalytic activity with the peak current density of 5.82 mA cm-2 at-0.39 V,which was ascribed to the synergistic effect of Fe-N-C active sites and PGR with good porous structures.The electron transfer number of 3.94 for the Fe-N-C/PGR composite indicated a direct four electron pathway for the ORR.In addition,the Fe-N-C/PGR composites showed good stability and high resistance to methanol compared with commercial 20%Pt/C catalysts.