Studies On Non-Pt-based Oxygen Reduction Reaction Electro-catalysts For Direct Methanol Fuel Cells

Electro-catalyst is one of the key materials in direct methanol fuel cells and strongly affect the performance,stability and durability of cells.Exploring cathodic electro-catalysts with low cost and methanol tolerant has important value both in theory and application for alkaline batteries.In this dissertation,Fe?@Pdx(x=0.5?1?2?3)nanoparticles prepared by the method of distribution reduction which ethylene glycol and sodium borate as reducing agents.X-ay diffusion(XRD)and transmission electron microscopy(TEM)show that Fe?@Pdx particles are spherical,Fe is completely coated by Pd,forming the core-shell structure.A series of Fe?@Pdx/C electro-catalysts were prepared by ultrasonic blending method.The effects of varying synthetic parameters,such as testing environments and Pd/Fe mass ratios on the oxygen reduction activity,stability and methanol tolerance.The results of linear sweep voltammetry curve and i-t curves show that Fe?@Pdx/C have higher oxygen reduction activity,methanol tolerance and better stability than Pd/C electrocatalyst in acid,acid methanol,alkaline,alkaline methanol conditions,this may attribute to the electronic effects and geometric effects between Pd and Fe.And with the increase of Pd's content,the oxygen reduction activity of the Fe?@Pdx/C catalyst show a trend of first increasing and then decreasing,the best oxygen reduction activity,stability and methanol tolerance of Fe?@Px,/C appears when the mass ratios of Pd/Fe is 2:1.Fe-N-C.Co-N-C.Cu-N-C electro-catalysts were synthesized by high temperature calcination with various metal elements.SEM and XRD show that Cu-N-C has serious agglomeration;Co-N-C particle are non-uniform in morphology;Fe-N-C with better dispersion,more porous.Linear sweep voltammetry curve and i-t curves test with different solutions under oxygen condition show that compare with Co-N-C and Cu-N-C,the limiting current density of Fe-N-C catalyst improves about 1.332mA/cm2,1.69mA/cm2 under acidic condition;increases 2.07mA/cm2,2.464mA/cm2 in acid methanol condition.Under these two conditions,the oxygen reduction activity,stability and methanol tolerance of Fe-N-C catalyst are better than others.The semi-potential and the limiting current density of Fe-N-C catalyst are higher than Co-N-C and Cu-N-C,so that the oxygen reduction activity,the stability and the anti methanol performance are the best in alkaline and alkaline methanol conditions.A series of Fe-Nx-C catalysts were prepared by changing the content of N.The effects of varying synthetic parameters,such as testing environments and the content of N on the oxygen reduction activity,stability and methanol tolerance.The result of SEM and XRD show that the framework of Fe-N1-C is not obvious;Fe-N2-C?Fe-N4-C have better dispersion,more porous and agglomeration;Fe-N6-C has a slight agglomeration.Electrochemical testing results indicate that with the increase of N's content?oxygen reduction activity,stability and methanol resistance show "Volcano type”in acidic and acidic methanol conditions,Among them,the oxygen reduction activity and the resistance to methanol of Fe-N2-C are the best,The stability of Fe-N2-C is same to Fe-N4-C.Compared with other catalysts,Fe-N4-C catalyst has higher activity,stability and methanol tolerance in alkaline and alkaline methanol conditions.