| Fuel cell is a kind of green energy technology,which owns environmental compatibility and high energy conversation efficiency.The oxygen reduction reaction occurring at the cathode plays a significant role in the operation of the fuel cells.The sluggish kinetics of ORR has severely hindered the widespread commercial applications of fuel cells.Platinum and platinum alloys are highly efficient oxygen reduction catalysts,however their scarcity and high cost greatly limit their application.Hence,intensive research has been devoted to the development of the highly efficient ORR catalysts.The monomeric metalloporphyrins were synthesized by template method,the polymeric metalloporphyrins were obtained by high temperature polymerization.Three-dimensional graphene(3D-G)was prepared by using coal tar pitch as carbon source and nano Mg O as a template.3D-G was used as support for poly-tetraphenylporphyrin Iron(PTPPFe)and poly-tetraphenylporphyrin cobalt(PTPPCo)to prepare PTPPFe/3D-G and PTPPCo/3D-G catalyst.The optimum preparation conditions of PTPPFe/3D-G and PTPPCo/3D-G catalyst were determined by investigating the effect of the ratio of raw materials and pyrolysis temperature on the catalytic performance.The optimum mass ratio of PTPPM(M=Fe,Co)and 3D-G was 1:1and the optimum pyrolysis temperature was 600°C.TEM,Raman,and XPS were employed to characterize the composition,structure and micro-morphology of the catalyst.TEM results show that PTPPFe/3D-G and PTPPCo/3D-G exhibited a foamy and porous graphene structure.PTPPFe?PTPPCo was uniformly distributed on the inner and outer surfaces of 3D-G.Raman results indicate that PTPPFe/3D-G and PTPPCo/3D-G consist of 4-6 layers of graphene.XPS results demonstrate that the active center of PTPPM/3D-G(M=Fe,Co)was M-N4(M=Fe,Co).Electrochemical tests conducted under alkaline conditions showed that the initial potential(Eonset)of PTPPFe/3D-G and half wave potential towards oxygen reduction reaction was 0.99 V and 0.81V(vs.RHE),respectively.The initial potential(Eonset)of PTPPFe/MWNT and half wave potential towards oxygen reduction reaction was 0.93 V and 0.78 V(vs.RHE),respectively.The initial potential(Eonset)of PTPPCo/3D-G and half wave potential towards oxygen reduction reaction was 0.97 V and 0.81 V(vs.RHE),respectively.The initial potential(Eonset)of PTPPCo/MWNT and half wave potential towards oxygen reduction reaction was 0.92 V and 0.77 V(vs.RHE),respectively.The electron transfer number of PTPPFe/3D-G and PTPPCo/3D-G was 3.99(@0.5 V vs.RHE)and 3.97(@0.5 V vs.RHE),respectively.The potential of PTPPFe/3D-G decreased with an attenuation of 14m V from cycle 1 to cycle 5000.The potential of PTPPCo/3D-G decreased with an attenuation of 14 m V from cycle 1 to cycle 5000.After the chronoamperometric test of40000 s,the current density of PTPPFe/3D-G and PTPPCo/3D-G is reduced by 16.5%and 18.79%.Electrochemical tests conducted under acidic conditions showed that the initial potential(Eonset)of PTPPFe/3D-G and half wave potential towards oxygen reduction reaction was 0.82 V and 0.60 V(vs.RHE),respectively.The initial potential(Eonset)of PTPPCo/3D-G and half wave potential towards oxygen reduction reaction was0.77 V and 0.59 V(vs.RHE),respectively.The potential of PTPPFe/3D-G decreased with an attenuation of 18.7 m V from cycle 1 to cycle 5000.The potential of PTPPCo/3D-G decreased with an attenuation of 19.9 m V from cycle 1 to cycle 5000.After the chronoamperometric test of 40000 s,the current density of PTPPFe/3D-G and PTPPCo/3D-G is reduced by 18.79%and 25.73%.Three-dimensional nitrogen-doped graphene(3D-NG)was prepared by using polyacrylonitrile(PAN)as nitrogen and carbon source and using zinc oxide as template.TEM images show that 3D-NG presented a foam porous structure.Results of XPS show that 3D-NG mainly contained two forms of nitrogen:pyridine nitrogen and pyrrole nitrogen,which is beneficial for oxygen reduction reaction.Results of electrochemical test performed under alkaline conditions show that the initial potential(Eonset)of 3D-NG and half wave potential towards oxygen reduction reaction was 0.98 V and 0.81 V(vs.RHE),respectively.The initial potential(Eonset)of 20 wt%Pt/C and half wave potential towards oxygen reduction reaction was 1.0 V and 0.82 V(vs.RHE),respectively.The electron transfer number of 3D-NG was 3.98(@0.5 V vs.RHE).The potential of3D-NG decreased with an attenuation of 14.5 m V from cycle 1 to cycle 5000.After the chronoamperometric test of 40000 s,the current density of 3D-NG is reduced by 18.34%.Electrochemical tests conducted under acidic conditions showed that the initial potential(Eonset)of 3D-NG and half wave potential towards oxygen reduction reaction was 0.82 V and 0.52 V(vs.RHE),respectively.The potential of 3D-NG decreased with an attenuation of 20 m V from cycle 1 to cycle 5000.After the chronoamperometric test of40000 s,the current density of 3D-NG is reduced by 25.4%.3D-NG was used as support for poly-tetraphenylporphyrin Iron(PTPPFe)and poly-tetraphenylporphyrin cobalt(PTPPCo)to prepare PTPPFe/3D-NG and PTPPCo/3D-NG catalyst.The optimum preparation conditions of PTPPFe/3D-NG and PTPPCo/3D-NG catalyst were determined by investigating the effect of the ratio of raw materials and pyrolysis temperature on the catalytic performance.The optimum mass ratio of PTPPM(M=Fe,Co)and 3D-NG was 1:1 and the optimum pyrolysis temperature was 600°C.TEM,Raman XRD and XPS methods were employed to characterize the composition,structure and micro-morphology of the catalyst.TEM results show that PTPPFe/3D-NG and PTPPCo/3D-NG exhibited a foamy and porous graphene structure.PTPPFe?PTPPCo was uniformly distributed on the inner and outer surfaces of 3D-NG.Raman results indicate that PTPPFe/3D-NG and PTPPCo/3D-NG consist of 4-6 layers of graphene.XPS results demonstrate that the active center of PTPPM/3D-NG(M=Fe,Co)was M-N4(M=Fe,Co).Electrochemical tests conducted under alkaline conditions showed that the initial potential(Eonset)of PTPPFe/3D-NG and half wave potential towards oxygen reduction reaction was 0.99 V and 0.82 V(vs.RHE),respectively.The initial potential(Eonset)of PTPPCo/3D-NG and half wave potential towards oxygen reduction reaction was 0.96 V and 0.82 V(vs.RHE),respectively.The electron transfer number of PTPPFe/3D-NG and PTPPCo/3D-NG was 3.99(@0.5 V vs.RHE)and3.97(@0.5 V vs.RHE),respectively.The potential of PTPPFe/3D-NG decreased with an attenuation of 13.7 m V from cycle 1 to cycle 5000.The potential of PTPPCo/3D-NG decreased with an attenuation of 13.5 m V from cycle 1 to cycle 5000.After the chronoamperometric test of 40000 s,the current density of PTPPFe/3D-NG and PTPPCo/3D-NG is reduced by 17.79%and 14.4%.Electrochemical tests conducted under acidic conditions showed that the initial potential(Eonset)of PTPPFe/3D-NG and half wave potential towards oxygen reduction reaction was 0.80 V and 0.63 V(vs.RHE),respectively.The initial potential(Eonset)of PTPPCo/3D-NG and half wave potential towards oxygen reduction reaction was 0.80 V and 0.59 V(vs.RHE),respectively.The potential of PTPPFe/3D-NG decreased with an attenuation of 16.5 m V from cycle 1 to cycle 5000.The potential of PTPPCo/3D-NG decreased with an attenuation of 17 m V from cycle 1 to cycle 5000.After the chronoamperometric test of 40000 s,the current density of PTPPFe/3D-NG and PTPPCo/3D-NG is reduced by 17.34%and 19.37%.In conclusion:the PTPPM/3D-G(M=Fe,Co)catalyst has better electrocatalytic oxygen reduction reaction activity than the PTPPM/MWNT(M=Fe,Co)catalyst;The PTPPM/3D-NG(M=Fe,Co)catalyst has better electrocatalytic oxygen reduction reaction activity than the PTPPM/3D-G(M=Fe,Co)catalyst;The electrocatalytic oxygen reduction performance of the polymerized porphyrin iron catalyst is superior to the polymerized porphyrin cobalt catalyst. |
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