The Synthesis And Oxygen Reduction Reaction Performance Research Of Pd-based Catalysts Supported On Carbon Matericals

Fuel cell is a kind of efficient and environmental power generation device,which having a broad application prospect in the distributed power generation,electric vehicles and other fields.But the commercialization process of fuel cell is severely restricted because of the huge demand for expensive Pt-based ORR catalysts.Therefore,the research and development of high efficiency,cheap ORR catalysts is of great significance.Pd-based catalysts are considered to be the most potential metal-based catalysts to replace Pt-based catalysts,due to the high ORR activity and relatively low prices.We have designed and synthesized the PdFe/CNT alloying catalysts,the PdFe/CNT-Supperlattice catalysts and the PdFePt/CNT catalysts with surface-enrich Pt,studied the influence regular between the composition,structure of catalysts and the ORR performance.Firstly,the PdFe/CNT alloying catalysts were synthesized by ethylene glycol reducing co-deposition with auxiliary NaBH4,studied the influence mechanism between the reaction system pH,the reaction system temperature and Pd/Fe ratio with the morphology and crystal structure of catalysts.Results show that the proper Pd/Fe ratio will promote the improvement of ORR activity due to the electronic effect and geometric effect.The Pd₇₅Fe₂₅/CNT catalyst has the best ORR activity,excellent methanol resistance and electrochemistry stability,its Ehalf-wave has enhanced 8 mV and 14 mV compared to the Pd/CNT catalyst in acidic and alkaline medium respectively.In order to enhance the ORR activity of PdFe/CNT alloying catalysts,the PdFe/CNT catalysts with L10-supperlattice crystal structure were synthesized by heat treatment.The result shows that the Ehalf-wave of PdFe/CNT alloying catalysts has enhanced 69 mV and the mass activity has increased 4.6 times?0.81 V vs.RHE?through the lattice transforma-tion.In addition,the PdFe/CNT-Supperlattice catalyst is a kind of ORR catalyst with high selectivity due to the excellent methanol resistance.Finally,the PdFePt/CNT catalysts with surface-enrich Pt were synthesized by atomic displacement.The result shows that the ORR activity and stability of the new catalysts are both better than the 20%commercial Pt/C,in spite of the load factor is just 7.05 wt%.The Eon-set and the Erhalf-wave of the PdFePt/CNT catalysts with surface-enrich Pt are 0.948 V and 0.861 V in acidic medium,which is 9 mV and 20 mV above the commercial Pt/C respectively.On the one hand,the excellent ORR activity was caused by the high utilization of Pt due to the surface-enrich Pt;on the other hand,the electronic properties of the superficial Pt atoms were modified by the charge transfer and strain effect between Pd,Fe and Pt,which improves the Pt-O adsorption intensity in ORR,thus accelerating the ORR reaction.