Preparation Of Pt - Based And Pd - Based Catalysts For Transition Metal Doping And Their Electrocatalytic Properties

Fuel cell is a high-efficient and green device of power generation. Especially, direct methanolfuelcell(DMFC)anddirectformicacidfuelcell(DFAFC)areconsideredtobethemostapplicationprospect of energy device. Platinum (Pt) electrode is still the most promising and commonly usedanode catalyst in DMFC. However, some disadvantages such as the limited nature reserve, veryexpensive price, readily adsorption and poison by CO, and improving electrochemical lifetimehinder its commercial application. Palladium (Pd) catalyst is an excellent catalyst in DFAFC but itselectrochemicalstabilityhasyettobeimproved.Based on the optimizing preparation conditions, this thesis had focused on the preparations,structure characterizations and electrocatalysis properties of Pt-based and Pd-based bimetalliccatalyststhroughaddingainexpensivetransitionmetal(suchasFe,Co,Ni)tonoblemetalsupportedon carbon black for DMFC and DFAFC. Some analysis techniques of X-ray diffraction (XRD),transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS) wereemployed to discuss the structure of these catalysts. Their electrochemical activities, stabilities andresistanceCOpoisonformethanolandformicacidoxidationwereevaluatedbycyclicvoltammetry,chronoamperometry, and CO stripping experiment. Natural chitosan polymer were also used topreparechitosan-carbonblackcompositeinpresentwork.ThecompositewasusedasthesupportofPt orPd catalyst to enhanceits electrochemical activityand stability. Based on the connection of thecatalysts’structure with their electrochemical properties, some innovative results were obtained andsummarizedasfollows:1. A optimizing preparation conditions has been obtained. The Pt-Ni/C catalyst was prepared bythe impregnation-chemical reduction method at the optimizing conditions including the reductionsolutionpH9,5%PtloadingsandPt/Niatomicratioof1:1.Thecatalystshowshighelectrochemicalactivityandstabilityinmethanolelectrocatalyticoxidation.2. Electrochemical measurements indicate that the catalytic activity for methanol oxidation onPt-M/C (M=Fe, Co, Ni) catalysts are better than Pt/C catalyst and has the following order of Pt/C <Pt-Fe/C <Pt-Ni/C <Pt-Co/C. Geometrically, the addition of second metal makes active Pt metalhavingsmallerparticles sizeandbetterhomogeneous dispersion.The results giverisetotheincrease of electrochemical surface area (ECSA) and the improvement of Pt particles efficience. ElectricallyStrong electron-donate effect of second metal decreases Pt2+ions concentration and increases Pt0surface concentration. The action of geometrical and electrical effects are responsible for highactivitiesandstabilitiesofPt-Co/CandPt-Ni/Ccatalysts.3. Meanwhile, Pd-M/C (M=Fe, Co, Ni) catalysts shown good performance in formic acidelectrocatalyticoxidationinfollowingorder:Pd/C <Pd-Fe/C <Pd-Ni/C<Pd-Co/C.Theadditionofthe second element to some extent decrease the size of Pd particles and improve the dispersion ofactivemetal.In addition, Pd-basedcatalysts shownhigher activitiesthanPt-based catalysts in formicacidelectrocatalyticoxidation.4. Chitosan-modified Pt catalyst and Pd catalyst exhibited higher catalytic activity and betterstability than unmodified catalysts for methanol and formic acid oxidation. The improvement ofmetal dispersion attributes to good ability capturing Pt or Pd particles of chitosan and inhibiting theaggregateofmetalparticles.