Study On Carbon-based Non-precious Metal Multicomponent Synergistic Oxygen Reduction Catalysts

The proton exchange membrane fuel cell is a clean and efficient energy conversion device.The kinetic rate of the cathodic oxygen reduction reaction and the electrode potential are the key factors affecting the efficiency of energy conversion.At the same time,the massive use of cathodic platinum-based catalysts in fuel cells is an important reason for the high cost of fuel cells.Due to the shortcomings of the most effective platinum-based catalysts,such as poor stability,high price,and limited reserves,the development of new high-efficiency oxygen reduction catalysts is an important content in the field of proton exchange membrane fuel cells.Non-platinum catalyst is one of the choices for future oxygen reduction catalysts.Among them,metal nitrogen carbon(M-N-C)materials have attracted much attention because of their considerable performance and low cost.In this thesis,metal-and non-metal-doped M-N-C catalysts were prepared from the perspective of synergistic control of activity,selectivity and stability.The main research contents are as follows:(1)BP 2000 carbon black with high specific surface areas and rich microporous structure was used as carbon source,melamine used as nitrogen source,and iron-zinc Prussian blue analog(FeZn-PBA)material used as iron source.Because zinc element effectively separated iron atoms and made it uniformly dispersed.In addition,the specific surface area,pore volume,metal content,and pyridine nitrogen were coordinated to increase the density of active sites and improve the performance of the catalysts.(2)Simulating the composition of biological enzymes,iron-copper Prussian blue analog was used as the metal source of metal-nitrogen-carbon catalysts,and FeCu-N-C catalyst was prepared by pyrolysis.In acidic media,the half-wave potential and limiting current density of the catalysts reached 0.784 V and 5.88 mA/cm2,respectively.The copper-based sites in the catalysts can reduce the two-electron product H2O2 in the oxygen reduction reaction,which improved the selectivity and stability of the catalysts.Its catalytic H2O2 reduction current was 6%to 20%larger than Fe-N-C.(3)Simultaneously improving the activity and stability of Fe-N-C catalysts by using copper and sulfur doping.Sulfur doping can increase the catalyst's TOF value to a greater extent than copper doping,and effectively reduce the hydrogen peroxide yield.Copper-sulfur doped Fe-N-C catalysts possessed higher TOF and lower hydrogen peroxide yield than Fe-N-C catalysts themselves.Sulfur-doped activated Fe-Nx sites and adjacent copper-based sites synergistically participated in the oxygen reduction reaction,thereby improving the catalyst activity and selectivity.Meanwhile,copper doping enhanced the stability of the catalyst by increasing the degree of graphitization of the catalysts,while sulfur doping reduced the degree of graphitization of the catalysts,which led to the deterioration of the catalysts performance.