Preparation And Study Of Bimetallic M/N/C Electrocatalysts For Oxygen Reduction Reaction In Proton Exchange Membrane Fuel Cells

Benefiting from high efficiency,no pollution and rapid response to load changes,polymer electrolyte membrane fuel cells(PEMFCs)has shown remarkable prospects in application of new energy vehicles.But the commercialization of PEMFCs has been limited due to the high cost of the precious Pt-based catalysts for oxygen reduction reaction(ORR).Hence the development of cheap and resource-rich pyrolytic metal and nitrogen-doped carbon(M/N/C)catalysts become the focus of current research.Among all the applicable catalysts,Fe/N/C catalysts show high expectations for relative good activity,but its poor stability and still insufficient activity is nonetheless an unresolved problem.Adding another metal site in Fe/N/C catalyst to construct bimetallic M/N/C catalyst is considered as an effective strategy.Therefore,this paper focused on the controllable design and performance regulation of bimetallic M/N/C catalysts for cathode ORR of proton exchange membrane fuel cells,including main research as follows:(一)Preparation and active site study of atomically dispersed FeCo/N-C eletrocatalysts(1)The atomically dispersed FeCo/N-C catalysts were prepared from bimetallic metal organic frameworks(BMOF)and introducing Fe phthalocyanine(FePc)molecules as iron precursor followed by pyrolysis.It has excellent performance in direct methanol fuel cell(DMFC)(100 mW cm-2).(2)Compared to the single metal FeN4 and CoN4 sites,DFT calculation manifests the enhanced O2 adsorption and elongated O-O bond lengths on bimetal FeCoN6 site,resulting the facile cleavage of the O-O bond and a direct 4e-process.(3)The stability and decay mechanism of the catalyst were discussed through rapid decay and Fenton-like reaction.The results indicate that the introduction of Co weaken the Fenton reaction of the catalyst while reducing the content of reactive oxygen free radicals,which restrain the loss of metal center and carbon corrosion to a certain extent to improve the overall stability of the catalyst.(二)Preparation and electrochemical performance study of highly active RuFe/N-C catalysts(1)A novel metal-organic gas doping method was proposed,in which the organic compound iron acetylacetone was thermal evaporated and then captured by RuNC with ZIF frame structure.The bimetallic RuFe/N-C catalyst was successfully constructed.(2)Electrochemical tests showed that the bimetallic RuFe/N-C catalyst exhibited great oxygen reduction activity approching that of commercial Pt/C.Due to the high intrinsic activity and abundant active site density of the bimetallic site,it exhibited an excellent power density(1.04 W cm-2)in hydrogen-oxygen fuel cells.(3)Stability experiment shows that the presence of Ru can inhibit the Fenton reaction of the catalyst and effectively reduce the generation of oxygen-containing free radicals,so that the bimetallic catalyst can still maintain good stability,reflecting the prospect of practical application.