| In the process of the development of direct methanol fuel cells(DMFCs),the cathodic oxygen reduction reaction(ORR)played an important role in the overall reaction efficiency of fuel cells.The scarcity and high cost of frequently-used Pt-based electrocatalysts for ORR had limited its commercialization.Heteroatom-doped carbon nano-materials had been affirmed to be one of efficient alternative catalysts for ORR.In this paper,N-GQDs used as ORR electrocatalysts,the influence of quality of C/N on catalytic activity and catalytic mechanism were investigated.This thesis was divided into two following parts:In the first part of the experiment,commercial N-GQDs were used as electrocatalysts,and TEM was used to characterize their dispersion and microstructure,moreover,various electrochemical measurements were carried out to characterize and test their catalytic activities for ORR in an alkaline medium.The results show that the quantity of GQD and N had different influences on the ORR catalytic activities.Potentials(peak position)became positive as quantity of N increases,while current mainly depends on the quantity of GQDs.C4N79(quantity of GQDs:0.2 mg,quantity of N:7.9×10-3 mg)shows a four-electron reduction process similar to Pt/C for ORR and better methanol tolerance.In the second part of the experiment,GO prepared by Hummers as raw materials,two-dimensional intermediate N-G was applied to obtain zero-dimensional final products N-GQDs by second hydrothermal treatment.We inspected effects of different proportion of urea content on electrocatalysis activity of N-GQDs.Characterization methods included transmission electron microscopy(TEM)and fourier transform infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS)and electrochemical methods.The results show that the diameters of N-GQDs were between 5-8 nm from intermediate N-G nanosheet.Under alkaline conditions,the effective nitrogen-doped intermediates and final products showed electro-catalysis activity,in which N-GQDs(35)and intermediates N-G(35)revealed better ORR catalytic activity with little difference,respectively 3.69,2.60 electronic process.N-GQDs(35)with relative low nitrogen doping content still remain stability,methanol tolerance,even more active site and close to 4 electronic reaction process.The phenomenon showed that except effective nitrogen doping,the higher degree of reduction and the quantum dot scale had significant contribution to alkaline ORR. |
