Preparation Of M-N-C Catalyst And Its Electrocatalytic Oxygen Reduction Reaction

Fuel cells are currently the most widely used energy conversion devices,and are green new energy sources.It has the advantages of high energy conversion efficiency,low environmental pollution and long service life.However,its further development is affected by the cathode catalyst problem.Precious metal platinum(Pt)and platinum-based catalysts are currently the most effective materials for oxygen reduction reactions(ORR)and are the most widely used.However,Pt first has low reserves,secondly expensive,and even poor stability.This series of problems requires researchers to study a cathode catalyst with low Pt and excellent electrocatalytic activity for use in ORR.Non-precious metal catalysts are an attractive alternative to Pt.Among them,transition metal-nitrogen-carbon(M-N-C)type catalysts have attracted extensive attention from researchers today because of their abundant sources,low cost,and strong electrochemical activity and corrosion resistance in ORR.In this paper,a series of new and effective M-N-C catalysts are prepared by selecting suitable transition metals,nitrogen sources and appropriate modification of graphene.It not only reduces the catalyst cost but also improves the catalytic performance of ORR.The specific work includes the following two Aspects:(1)The spontaneous polymerization of dopamine(DA)on graphene oxide(GO)to form PDA-GO,followed by doping Co2+ ions to synthesize Co-PDA-GO,followed by carbonization at 900 °C to obtain Co-N-GO catalyst.The morphology,structure and composition of Co-N-GO were characterized by SEM,TEM,XRD,et al.The presence of abundant Co-N active sites and Co nanoparticles in the catalyst was found to enhance ORR activity.The catalytic activity of the oxygen reduction reaction in a0.1 M KOH electrolyte was tested using a rotating disk electrode.The results of the Co-N-GO show that the initial potential reach 0.97 V,half-wave potential reach0.86 V and limiting current density catalyst reach 5.25 m A cm-2,respectively.showing an ORR activity similar to Pt/C(0.98 V,0.85 V and 5.34 m A cm-2).It has been calculated that the catalyst achieves an effective four-electron oxygen reduction reaction.The stability test was carried out by the chronoamperometry.After 15000 s of testing,the current density of the Co-N-GO catalyst was only decreased by 6%.Under the same conditions,the Pt/C decreased by about 30%.Finally,the catalyst was tested formethanol resistance and compared with commercial Pt/C,it was found that commercial Pt/C decreased by 80%,while Co-N-GO catalyst decreased by only 3%.Therefore,the Co-N-GO catalyst exhibits better methanol tolerance and long-term durability.(2)The graphene oxide is etched using hydrogen peroxide as a carrier,and then hemin is loaded to synthesize a porous Fe-N-HGO catalyst to achieve an effective four-electron oxygen reduction reaction.This experiment systematically studied the morphology,doping properties and ORR activity of the catalyst.The results show that the initial potential,half-wave potential and limiting current density reach 0.92 V,0.81 V and 5.71 m A cm-2,respectively,which are close to or even better than commercial Pt/C and effective four-electron reduction path.After the stability test,it was found that the current density of Fe-N-HGO only decreased by 8%(commercial Pt/C decreased by 30%).It shows that the stability of Fe-N-HGO is superior.Finally,the catalyst was tested for methanol resistance,and it was found that the Fe-N-HGO catalyst only decreased by 2% commercial(the performance of Pt/C decreased by80%).The results show that the material is superior to the Pt-based catalyst under the same conditions.